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Technical terms used across HortGuide, defined for the field. 237 terms
Fine roots with functional root hairs responsible for the uptake of water and dissolved minerals. Short-lived and concentrated near root tips, absorbing roots represent the active interface between tree and soil. Most are found in the top 12 to 18 inches of the soil profile.
See also: rhizosphere , mycorrhizal , root cap
Growth or movement directed toward the tip of a shoot or branch. Fire blight spreads acropetally through vascular tissue. The opposite of basipetal.
See also: basipetal
The pest or disease population level at which management intervention becomes justified. Below the threshold, the cost of treatment outweighs the damage; above it, damage accelerates. IPM programs are built on thresholds rather than calendar spraying.
Any substance added to a spray tank to improve performance. Surfactants, stickers, spreaders, and pH buffers are all adjuvants. Copper fungicide applications in particular benefit from proper adjuvant use.
See also: surfactant
Arising from an unusual position on a plant, without connection to existing meristems or buds. Most commonly describes roots that form on buried trunk tissue (from too-deep planting or mulch volcanoes) or shoots that emerge from wound sites. Adventitious roots from buried trunks often circle or girdle the stem, creating long-term structural problems.
Soil or sediment deposited by flowing water (rivers, streams, floods). Alluvial soils on valley floors are typically finer-textured and more fertile than upland glacial soils because running water sorts and deposits sediment by size, leaving finer materials in low areas. In the Puget Sound lowlands, Puyallup, Woodinville, and Briscot series are river-terrace alluvial soils.
See also: glacial-till
Any material mixed into soil to improve its physical or chemical properties. Comite, aged bark, and composted leaf mold are common organic amendments in the Puget Sound lowlands. Amendments improve drainage in clay soils and water retention in sandy soils, but they are not the same as fertilizer.
Hormonal suppression of lateral bud growth by the terminal bud, mediated primarily by auxin. Removing the terminal bud (by pruning or breakage) releases lateral buds from suppression, triggering side shoot development. This mechanism explains why heading cuts produce bushy regrowth and why topping stimulates watersprout proliferation.
See also: apical meristem , epicormic sprouting
Growing point at the tips of shoots and roots where active cell division occurs. The apical meristem at a shoot tip is enclosed within the terminal bud and is responsible for all primary (lengthwise) growth. Root apical meristems are protected by a root cap.
See also: primary growth , terminal-bud
The most common type of mycorrhizal fungi, partnering with roughly 70 percent of all plant species including maples, fruit trees, ornamental shrubs, lawn grasses, and vegetable crops. Abbreviated AMF. Unlike ectomycorrhizal fungi, AMF penetrate directly through the root cell wall and form a highly branched structure called an arbuscule inside each cell, where nutrient and carbon exchange occurs. AMF produce no external fungal sheath around the root tip.
See also: mycorrhizal , arbuscule , ectomycorrhizal , extramatrical-mycelium
A highly branched, tree-shaped structure formed by arbuscular mycorrhizal fungi (AMF) inside individual root cortex cells. The arbuscule is the primary site of nutrient and carbon exchange in AMF partnerships: the plant transfers sugars outward across the arbuscule membrane while the fungus delivers phosphorus, nitrogen, and water inward. Individual arbuscules are short-lived, typically collapsing within days and being replaced by new ones further along the growing root.
See also: arbuscular-mycorrhizal , mycorrhizal
A scale insect (family Diaspididae) covered by a waxy plate that separates from the insect body underneath. Armored scales produce no honeydew, cause direct tissue damage through feeding on plant cells, and typically have one generation per year in the Puget Sound region.
See also: soft scale , crawler , honeydew
A sexual spore produced inside a sac-like structure (ascus) by fungi in the phylum Ascomycota. In apple scab, ascospores form over winter inside pseudothecia in fallen leaf litter and are forcibly discharged into the air during spring rains, initiating the primary infection cycle.
See also: conidium , pseudothecium
Biological pest control via periodic release of commercially reared natural enemies (parasitoids, predators, or pathogens) to boost local populations above what habitat alone can sustain. Examples: releasing Trichogramma wasps for caterpillar egg control, or Aphidius colemani for greenhouse aphid control. Distinguished from conservation biocontrol (protecting what is already there) and classical biocontrol (importing species from the pest's native range for permanent establishment). Most garden beneficials sold in catalogs are augmentative biocontrol agents.
See also: conservation biocontrol , classical biocontrol , biocontrol agent
A naturally occurring soil bacterium that produces proteins toxic to specific insect groups when ingested. The kurstaki variety (Btk) targets caterpillars (Lepidoptera larvae) and is widely used in both organic and conventional pest management. Must be eaten by actively feeding larvae to work; it is not a contact insecticide. Breaks down quickly in sunlight.
See also: IPM , action threshold
Growth or movement directed toward the base of a shoot or root. Verticillium wilt moves basipetally in the vascular system, which is why symptoms appear in the upper canopy first. The opposite of acropetal.
See also: acropetal
A standardized numerical scale for describing plant growth stages, from seed germination (00) through senescence (97). Each two-digit code identifies a specific phenological event. HortGuide uses BBCH codes in the field observation log to standardize event recording across species.
A raised strip 2 to 5 feet wide planted with native perennial bunchgrasses, left permanently undisturbed, established along field or garden edges to serve as year-round refuge and overwintering habitat for ground beetles (Carabidae) and other ground-dwelling predators. Developed as a UK agricultural conservation practice in the 1980s. In the Pacific Northwest, recommended species include Roemer's fescue (Festuca roemeri), tufted hairgrass (Deschampsia cespitosa), and blue wildrye (Elymus glaucus). Takes two to three years to reach full function.
See also: conservation biocontrol , carabidae , hedgerow
A living organism (bacterium, fungus, or predator) used to suppress a pest or pathogen. For gray mold, Trichoderma and Bacillus species are the most studied biocontrol agents. Efficacy in cool, wet field conditions is variable; the PNW Plant Disease Management Handbook notes limited effectiveness in Pacific Northwest conditions.
See also: fungicide resistance
A specific, observable biological event used as the starting point for a degree-day accumulation model. For apple scab, the biofix is 50% green tip on McIntosh flower buds (Gadoury & MacHardy 1982). Different pest and disease models use different biofix events.
See also: GDD
The phase of fire blight infection that enters through open flowers. Bacteria infect the stigma, nectary, or other floral tissues of open blossoms and progress down the branch from the flower cluster. Blossom blight is the primary fire blight infection pathway; bloom period management targets this entry point.
See also: fire-blight , shoot-blight
Physiological disorder (not a disease) causing sunken, dark lesions on the blossom end of fruit. Caused by calcium uptake disruption, usually from inconsistent watering rather than calcium deficiency in the soil. Most common in tomatoes and peppers.
The first fig crop of the season, produced on the previous year's wood. Breba figs develop as embryos at leaf nodes during summer, overwinter as pea-sized bumps near branch tips, and ripen the following July or August. In the Puget Sound lowlands, the breba is the primary (and often only) reliable fig harvest because summer heat is insufficient to ripen the main crop on most varieties.
See also: main-crop , parthenocarpy
The moment a dormant bud splits open and new growth becomes visible. Budbreak timing is driven by accumulated heat (GDD) after sufficient chill hours have been met. In the Puget Sound lowlands, most deciduous trees break bud between late February and mid-April depending on species.
See also: chill hours , dormancy , GDD
A soil's resistance to pH change from amendments, driven primarily by clay content, organic matter, and cation exchange capacity (CEC). Soils with high buffer capacity (Bellingham clay, Seattle organic muck) require more lime or sulfur to shift pH than soils with low buffer capacity (Everett gravelly sandy loam).
An underground storage organ made of fleshy scales (modified leaves) arranged concentrically around a basal plate. True bulbs (Narcissus, Tulipa, Allium, Hyacinthus) store carbohydrates between growing seasons to fuel the next year's growth and bloom. Distinct from corms (Crocus, Gladiolus), tubers (Dahlia), and rhizomes (Iris), which store energy in different tissue types.
See also: vernalization , senescence , dormancy
The dry weight of soil per unit volume, measured in grams per cubic centimeter (g/cm³). Bulk density indicates soil compaction. Healthy loam: 1.1-1.3 g/cm³. Compacted urban soil: 1.8-2.0 g/cm³. Higher bulk density restricts root growth and water movement. Organic matter incorporation and reduced traffic lower bulk density.
See also: soil-structure , compaction , organic-matter
A plant that tolerates or prefers alkaline soil (pH above 7.0). Asparagus, clematis, lavender, and lilac are calcicoles commonly grown in the Puget Sound region. Opposite of calcifuge.
A plant that requires or strongly prefers acidic soil (typically below pH 6.0) and suffers in alkaline conditions. Rhododendrons, blueberries, azaleas, pieris, heathers, and camellias are common calcifuges in Puget Sound gardens. Opposite of calcicole.
See also: calcicole , soil pH , interveinal chlorosis
The diameter of a tree trunk, measured six inches above the soil line for trees under four inches, and twelve inches above for larger trees. Caliper is the nursery industry standard for sizing shade and street trees.
Undifferentiated tissue formed by the cambium at the margins of a wound. Callus is the initial wound response; it later differentiates into woundwood as the tissue lignifies and organizes. Not a synonym for woundwood.
The collective term for the sepals of a flower. In apple and pear fruit, the calyx persists as the indented blossom end opposite the stem. This is a common entry point for codling moth larvae boring into the fruit.
The thin layer of actively dividing cells between bark and wood that produces new growth each year. All radial trunk growth originates here. Damage to the cambium from construction equipment, weed trimmers, or girdling roots is often fatal because the tree cannot repair the vascular connection.
A larval body shape characterized by an elongated, flattened form with well-developed legs, sclerotized (hardened) head capsule, and forward-projecting mandibles, adapted for active predation. Ground beetle (Carabidae), rove beetle (Staphylinidae), and lacewing (Chrysopidae) larvae are campodeiform. Distinguished from the C-shaped, soft-bodied scarabaeiform larvae typical of root-feeding beetle grubs.
A localized area of dead bark and cambium on a branch or trunk, often sunken or discolored. Cankers may be caused by fungi, bacteria, or environmental stress. Fire blight bacteria overwinter in cankers, making them both a symptom and a source of reinfection.
A nesting strategy in which bees use pre-existing holes (beetle galleries, hollow stems, woodpecker holes, artificial tubes) rather than excavating their own. Mason bees and leafcutter bees are cavity nesters. Providing appropriate cavities is a primary conservation action for these species.
See also: solitary bee
Cation exchange capacity: a measure of a soil's ability to hold positively charged nutrients (calcium, magnesium, potassium, ammonium) against leaching. Measured in milliequivalents per 100 grams (meq/100g). Higher CEC soils retain nutrients better. Clay and organic matter increase CEC. Target range for Puget Sound gardens: 10-20 meq/100g.
See also: soil-texture , organic-matter
Hours of exposure to temperatures between 32°F and 45°F during winter dormancy. Many deciduous trees and fruit crops require a species-specific accumulation of chill hours before they can respond to spring warmth. The Puget Sound lowlands typically provide 800 to 1,200 chill hours per winter.
See also: dormancy , budbreak , vernalization
A thick-walled resting spore produced by certain fungi and oomycetes as a survival strategy during unfavorable conditions. Phytophthora produces chlamydospores that persist in soil for years and germinate when soil becomes saturated, initiating new infection cycles.
See also: zoospore , oospore , inoculum , sporulation
Yellowing of leaf tissue due to insufficient chlorophyll production. Causes include nutrient deficiency (especially iron in high-pH soils), root damage, poor drainage, and disease. Interveinal chlorosis (yellowing between green veins) is a common diagnostic pattern.
See also: necrosis
The introduction of natural enemies (parasitoids, predators, or pathogens) from an invasive pest's native range to establish permanent, self-sustaining biological control in the pest's introduced range. Distinguished from augmentative biocontrol (periodic release of commercially reared organisms) by the goal of permanent establishment. USDA has released four parasitoid wasp species from China for classical biocontrol of emerald ash borer, three of which have established self-sustaining populations.
See also: parasitoid
A silken case spun by a mature caterpillar as a protective covering for pupation, the transformation from larva to adult moth or butterfly. Tent caterpillar cocoons are tan and loosely woven, typically found in sheltered spots away from the host tree: under eaves, in leaf litter, on fences.
See also: instar
Two or more stems of roughly equal diameter originating from the same point or from points very close together on a trunk. Codominant stems often develop tight V-crotches with included bark and are a primary structural defect addressed in young tree pruning.
See also: included bark
A shared fungal network connecting the roots of multiple plants of the same or different species through overlapping mycorrhizal associations. Carbon, water, and nutrients can move between plants through the network, though research suggests transfer amounts are modest relative to what individual trees produce on their own. Also called the CMN or, colloquially, the "wood wide web." Well documented in Pacific Northwest conifer forests, where more than 95 percent of western hemlock root tips share fungal partners with surrounding Douglas-fir.
See also: mycorrhizal , ectomycorrhizal , extramatrical-mycelium
Reaction wood in conifers, formed on the underside of a leaning stem. Pushes the stem back toward vertical. Denser than normal wood, with rounded tracheids in cross-section and up to six times greater longitudinal shrinkage when dried.
See also: reaction wood , tension wood
An asexual spore produced by many fungi, typically on the surface of infected tissue. In apple scab, conidia form on leaf lesions 15 to 18 days after infection and splash to new leaves via rain, driving secondary infection cycles throughout the growing season. Plural: conidia.
See also: ascospore
Biological pest control that relies on protecting and encouraging naturally occurring beneficial organisms already present in the landscape, rather than importing or releasing them. Tools are habitat (permanent mulch, undisturbed edges, beetle banks, hedgerows) and pesticide discipline (avoiding broad-spectrum residues that kill predators alongside pests). Distinguished from augmentative biocontrol (periodic commercial releases) and classical biocontrol (introductions from a pest's native range). Ground beetles, rove beetles, and most spiders are managed almost entirely through conservation biocontrol because they are not commercially reared.
See also: augmentative biocontrol , classical biocontrol , biocontrol agent , beetle bank
Vegetables that germinate and thrive in cool soil (40 to 60°F) and prefer air temperatures below 70°F: lettuce, spinach, peas, broccoli, cabbage, kale, arugula. Cool-season crops are planted in early spring (March to April in the Puget Sound lowlands) and often again in late summer for fall harvest. They tolerate light frost and actually improve in flavor after cold exposure.
See also: warm-season crops
A pair of small tube-like projections on the rear end of an aphid that function as exhaust pipes, releasing defensive compounds. Cornicles are a diagnostic feature distinguishing true aphids from similar-looking insects like whiteflies and psyllids.
A branched flower cluster where the outer flowers sit on longer stalks than the inner ones, producing a flat-topped or slightly rounded inflorescence with all the flowers at roughly the same height. The base form of most hydrangea flower heads (smooth, bigleaf, mountain, oakleaf). Compare with panicle, where the flower cluster is cone-shaped or pyramidal rather than flat-topped.
The mobile, first-instar nymph or larval stage of scale insects. Crawlers are the only exposed, vulnerable life stage of scale, and all contact-based treatments must target crawler emergence. Timing by GDD is critical for effective management.
See also: armored scale , soft scale , instar
Active primarily during twilight periods at dawn and dusk. Codling moth adults are crepuscular, flying and mating at dusk when evening temperatures exceed 62 degrees Fahrenheit.
A plant variety that has been selected and propagated for specific desirable traits: flower color, disease resistance, growth habit, fruit quality. Cultivar names appear in single quotes after the species name: Acer palmatum 'Bloodgood'. Not all named plants are cultivars; some are botanical varieties that occur in the wild.
See also: variety , rootstock , scion
A diagnostic indicator of flatheaded borer (family Buprestidae) emergence. The adult beetle chews through bark leaving a hole shaped like a capital D, approximately 3-4 mm across. Specific to buprestid beetles including emerald ash borer and bronze birch borer. Distinguished from the round exit holes left by bark beetles and roundheaded borers (family Cerambycidae).
See also: emerald ash borer , frass
Number of days from transplanting (or direct seeding, depending on the crop) to first ripe fruit. Varies by climate. In the Puget Sound lowlands, add 10 to 14 days to packet estimates in cooler microclimates.
Removing spent flowers from plants. Beyond aesthetics, deadheading removes the tissue most vulnerable to Botrytis infection and eliminates inoculum sources for secondary spread. Particularly important for roses, peonies, and rhododendrons in wet spring weather.
See also: sanitation , gray mold
An insect that feeds on leaves, sometimes stripping foliage from entire branches or trees. Tent caterpillars, fall webworm, and winter moth are common defoliators in the Puget Sound region. Most healthy established trees recover from a single defoliation event by pushing a second flush of leaves.
See also: action threshold
A growth habit in which a plant reaches a genetically determined mature size and stops growing, flowering all at once or in a concentrated flush. Determinate tomatoes and beans are compact, ideal for containers and small spaces, and mature all fruit at once, which is useful for canning. The opposite of indeterminate.
See also: cultivar
A period of suspended development in insects, triggered by environmental cues like shortening day length or cooling temperatures. Similar to dormancy in plants but specific to arthropods. Many overwintering pests enter diapause in fall and resume development in spring when GDD accumulation resumes.
Progressive death of branches starting at the tips and moving toward the trunk. Dieback is a symptom, not a diagnosis: it can result from drought stress, root damage, vascular disease (Verticillium, Phytophthora), canker infections, or winter injury. The pattern and speed of dieback help distinguish causes.
Wood anatomy pattern in which vessels are distributed relatively evenly across the entire growth ring, with little size contrast between earlywood and latewood. Bigleaf maple and red alder are diffuse-porous species.
See also: ring porous , vessel
Planting seeds directly into garden soil at their final spacing, rather than starting them indoors in containers for later transplanting. Direct sowing works best for crops with fragile root systems or rapid germination: beans, peas, carrots, radishes, squash. In the Puget Sound lowlands, timing is critical to avoid cold, wet soil that rots seed.
See also: soil temperature , seedling
Letter codes on seed packets or plant labels indicating bred resistance to specific pathogens. Common codes for tomato: V (Verticillium), F/FF/FFF (Fusarium races 1/2/3), N (nematodes), T (tobacco mosaic virus), Ph (Phytophthora/late blight). Resistance is not immunity.
See also: resistance
Ground limestone containing both calcium carbonate and magnesium carbonate. Raises soil pH while supplying magnesium. Preferred over calcitic lime when soil tests show low magnesium levels.
A period of minimal metabolic activity and suspended visible growth. In the Puget Sound lowlands, most deciduous trees are dormant from leaf drop (November) through budbreak (February to April). Dormancy is the safest window for pruning disease-susceptible species because pathogens are also inactive.
See also: chill hours , budbreak , diapause
A USDA classification describing how quickly water moves through soil in response to gravity. Ranges from "excessively drained" (water moves too fast) to "very poorly drained" (water pools for months). Drainage class depends on texture, soil structure, slope, and subsurface features like hardpan. Critical for plant selection and management strategy.
See also: percolation-rate , perched-water-table , hardpan
The imaginary circle on the ground directly below the outermost edge of a tree's canopy, where rain drips off the leaves. Feeder roots concentrate in a zone extending from the trunk to well beyond the drip line. Fertilizer, mulch, and irrigation should target this zone.
The portion of a growth ring produced during the rapid spring growth flush. Characterized by large, thin-walled cells optimized for water transport. In ring-porous species, the large vessels visible in end grain are earlywood.
See also: latewood , ring porous
A genetically distinct population of a species adapted to particular local environmental conditions. Native groundcover ecotypes from coastal sites may differ in vigor, drought tolerance, and establishment rate from populations collected inland. Sourcing local ecotypes improves establishment success.
See also: cultivar
A type of mycorrhizal fungi that forms a visible pale sheath (the fungal mantle) around the outside of each root tip, with threads slipping between the outer root cells to form the nutrient-exchange zone called the Hartig net. Abbreviated ECM. ECM fungi never penetrate the root cells themselves. They partner with conifers (Douglas-fir, hemlock, pine, spruce, cedar), oaks, birch, alder, hazel, larch, linden, walnut, and redbud. Most edible forest mushrooms (chanterelles, porcini, Amanita) are ECM fungi fruiting above the roots they colonize.
See also: mycorrhizal , hartig-net , fungal-mantle , extramatrical-mycelium , arbuscular-mycorrhizal
Pure sulfur applied to soil to lower pH. Requires microbial oxidation by Thiobacillus bacteria to produce sulfuric acid; works slowly (3 to 6 months). Most cost-effective acidifier for home garden use. Best applied in spring in the Puget Sound region when soil biology is active.
The hardened, modified forewings of beetles (order Coleoptera) that cover and protect the membranous hindwings and abdomen when the beetle is not in flight. Elytra meet in a straight line down the middle of the back and typically show species-level identification features (grooves, punctation, color, sculpture). In flightless beetles such as Scaphinotus and Omus, the elytra are fused together and the hindwings are absent or reduced.
See also: coleoptera , carabidae
An invasive metallic green beetle (Agrilus planipennis, family Buprestidae) native to northeastern Asia that kills ash trees (Fraxinus) by larval feeding in the phloem and outer sapwood. First detected in North America near Detroit in 2002; first West Coast detection in Forest Grove, Oregon, June 2022. Larvae create S-shaped galleries that disrupt nutrient and water transport, causing crown dieback and typically killing untreated trees within 3-5 years.
See also: frass , phloem , cambium , trunk injection
Production of new shoots from dormant or adventitious buds on the trunk or major limbs, triggered by stress, canopy loss, or sudden light exposure. Common on ash trees infested with emerald ash borer, where trunk sprouts appear below the dying upper canopy as the tree attempts to replace lost leaf area. Also seen after heavy pruning, storm damage, or root disturbance.
See also: cambium
A specialized type of mycorrhizal fungi that partners exclusively with plants in the heather family (Ericaceae), including salal, kinnikinnick, rhododendron, blueberry, madrone, and heather. Ericoid fungi evolved with these plants in acidic, high-organic soils and are highly specific to the Ericaceae. Construction grading that strips topsoil eliminates ericoid fungi along with the soil horizon, which is one reason Ericaceae plantings on disturbed urban sites often fail to establish.
See also: mycorrhizal , ectomycorrhizal , arbuscular-mycorrhizal
An abnormal, hair-like or felt-like growth on a plant leaf caused by eriophyid mite feeding. Erineums appear as velvet patches or blistered areas and are the plant's defensive response to mite irritation. Damage is cosmetic; the plant remains unharmed.
See also: gall
A training method in which a tree or shrub is grown flat against a wall, fence, or trellis system, with branches trained along horizontal wires. Used for fruit trees in space-limited sites and to capture reflected heat from south-facing walls, extending the growing season for heat-loving species like figs.
See also: heading cut , thinning cut
Bark that peels, flakes, or sheds in layers, revealing contrasting inner bark. Paperbark maple (Acer griseum), stewartia, and river birch are valued for their exfoliating bark. The characteristic is ornamental, not a sign of disease.
The portion of a mycorrhizal fungal network that extends beyond the root surface into the surrounding soil. The extramatrical mycelium threads through soil pore spaces too small for any root to enter, extending the plant's effective uptake zone from millimeters (root hair reach) to centimeters or meters. This is the structural mechanism by which mycorrhizal fungi increase phosphorus, water, and trace nutrient acquisition for their plant partners.
See also: mycorrhizal , ectomycorrhizal , arbuscular-mycorrhizal
Fungicide Resistance Action Committee classification that groups fungicides by their biochemical mode of action. Rotating between FRAC groups slows resistance development because each group targets a different pathway in the pathogen. Example: FRAC 7 (SDHIs like boscalid) and FRAC 11 (QoIs like pyraclostrobin) are different groups.
See also: fungicide resistance , mode-of-action
Insect excrement, often visible as fine sawdust-like material at the base of a tree or in bark crevices. Frass is a key diagnostic indicator for boring insects like bronze birch borer and bark beetles. The color and texture of frass can help identify the species responsible.
See also: honeydew
A soil consistency term meaning the soil crumbles easily when moist, neither clumping nor falling apart into dust. Friable soil is desirable for root growth, seed germination, and cultivation. Friability indicates good structure, adequate organic matter, and minimal compaction.
See also: soil-structure , bulk-density
The visible pale sheath of fungal tissue that coats each root tip in an ectomycorrhizal (ECM) partnership. The mantle is the structure most easily seen when ECM-colonized roots are examined: swollen, club-shaped root tips enclosed in a fuzzy white or cream-colored sheath. In addition to its role in the nutrient exchange structure (the Hartig net forms just inside it), the mantle provides a physical barrier against some soil-borne pathogens.
See also: ectomycorrhizal , hartig-net
The inherited ability of a pathogen population to survive exposure to a fungicide that previously controlled it. Develops through selection pressure when the same FRAC group is applied repeatedly, favoring individuals with mutations that confer tolerance. In Puget Sound Botrytis populations, resistance to multiple FRAC groups is widespread.
See also: FRAC group
An abnormal swelling or outgrowth on plant tissue caused by insects, mites, fungi, or bacteria. Galls on leaves are usually cosmetic. Galls on stems or roots (like crown gall caused by Agrobacterium tumefaciens) can be structurally significant.
A class of mollusks (Gastropoda) including slugs and snails. Literally "stomach-foot," referring to the muscular ventral foot used for locomotion. Garden pest slugs and snails are terrestrial gastropods in the order Stylommatophora.
See also: radula , molluscicide
Growing degree days: a measure of accumulated heat used to predict biological events like pest emergence, bloom timing, and disease risk. Calculated by summing daily heat units above a base temperature. HortGuide uses GDD base 32°F (GDD₃₂) as the site-wide standard; source base temperatures are recorded in profiles for traceability.
See also: phenology , BBCH , chill hours
A predator that feeds on a wide range of prey species rather than specializing on one or a few. Generalist predators are valuable in integrated pest management because they are present and hunting before pest populations reach economic threshold, rather than arriving only after prey density triggers a specialist response. Most ground beetles, wolf spiders, and harvestmen are generalist predators. The tradeoff is that per-capita control of any single pest species is lower than what a dedicated specialist delivers.
See also: biocontrol agent , conservation biocontrol , parasitoid
Unsorted sediment (clay, silt, sand, gravel) deposited directly by glacial ice, without the sorting that water provides. In the Puget Sound lowlands, the Vashon ice sheet deposited till roughly 15,000 years ago, which forms the parent material for upland soils like Alderwood. Till is characteristically dense, heterogeneous, and often contains a compacted lower layer (hardpan) that restricts water movement and root growth.
A sticky glycoprotein produced by arbuscular mycorrhizal fungi (AMF) that coats fungal threads and binds soil mineral particles into stable aggregates. Glomalin improves soil structure by creating clumps of soil particles (aggregates) that resist compaction, improve drainage, and increase water-holding capacity. It is one of the primary mechanisms by which healthy mycorrhizal communities contribute to soil resilience.
See also: arbuscular-mycorrhizal , mycorrhizal
A naturally occurring baculovirus that infects a specific insect species. Codling moth granulosis virus (CpGV) is commercially available as Cyd-X and Madex HP and is approved for organic production. Larvae ingest virus particles while feeding on treated fruit surfaces.
See also: biological-control
Common name for disease caused by Botrytis cinerea, referring to the distinctive gray, fuzzy sporulation visible on infected tissue. The gray coating is a mass of conidia (asexual spores) produced on the surface of dead or dying plant parts. Affects more than 200 plant species across fruit, ornamental, vegetable, and herb categories.
See also: conidium , botrytis-cinerea
The gradual acclimation of seedlings to outdoor conditions before permanent transplanting. Hardening off means moving seedlings to a sheltered outdoor location for a few hours daily, increasing exposure over about a week to allow them to adjust to wind, direct sun, and temperature swings. Skipping this step results in wilted, burned, or killed transplants.
See also: seedling
A dense, compacted subsurface soil layer that restricts root penetration and water movement. In the Puget Sound lowlands, most hardpan is glacially deposited material (densic layer or duripan) found at 18 to 36 inches depth in soils like Alderwood. Creates seasonal perched water tables in winter when water pools above the impermeable layer.
See also: perched-water-table , glacial-till
The network of ectomycorrhizal (ECM) fungal threads that slip between the outer cortex cells of a colonized root tip, forming the primary zone of nutrient and carbon exchange in ECM partnerships. Named for the German forester Robert Hartig. The Hartig net surrounds individual root cells without penetrating them, creating a high-surface-area contact zone where the plant transfers sugars to the fungus and the fungus delivers phosphorus, water, and trace nutrients to the plant.
See also: ectomycorrhizal , fungal-mantle
A pruning cut that removes the terminal portion of a branch, shortening it to a bud, lateral branch, or stub. Heading cuts stimulate new growth below the cut, producing multiple shoots. Used to reduce height, encourage branching, or force lateral bud break on young trees during training.
See also: thinning cut , watersprout
The central core of dead xylem cells in a trunk or branch. No longer conducts water; serves as structural support. Typically darker and harder than sapwood, and more resistant to decay because of extractive chemicals (resins, tannins, phenolics) deposited as sapwood ages.
Open-pollinated variety maintained by selection for multiple generations, typically 50 or more years. Valued for flavor diversity but generally lacking modern disease resistance bred into hybrid varieties.
See also: hybrid , open-pollinated
A silken cocoon or shelter constructed by an insect larva for overwintering or pupation. Codling moth larvae spin hibernacula under loose bark, in soil crevices, and in sheltered debris at the base of host trees. Plural: hibernacula.
See also: diapause
A fire blight canker that survived the previous growing season and overwinters in living branch tissue. Holdover cankers are the primary inoculum source the following spring: bacteria at the canker margin become active as temperatures warm, producing visible ooze that insects carry to open flowers. Dormant removal of holdover cankers is the most effective long-term management practice for fire blight.
See also: canker , inoculum , fire-blight
A sticky, sugary liquid excreted by sap-feeding insects including aphids, soft scales, mealybugs, and whiteflies. Honeydew coats surfaces below the canopy and serves as a substrate for sooty mold. Its presence is often the first visible sign of an infestation above.
See also: frass
An older horticultural name for the mophead flower form of Hydrangea macrophylla. The term originated in eighteenth-century European nursery trade and persists in some regional and international literature; in American usage it has largely been replaced by "mophead." When a source refers to "hortensia hydrangeas" it is almost always referring to mophead bigleaf hydrangeas specifically, not to all hydrangeas.
The set of plant species a pathogen or pest can infect or feed on. Broad host range pathogens like Verticillium dahliae (hundreds of species) are harder to manage through crop rotation or replacement planting than narrow host range organisms.
See also: susceptibility , resistance
First-generation cross (F1) between two genetically distinct parent lines. Exhibits hybrid vigor (heterosis) and uniform performance. Seeds saved from F1 hybrids do not breed true to the parent type.
See also: heirloom , open-pollinated
Producing flowers before leaves emerge. Most cherries (Prunus), magnolias, and witch hazels are hysteranthous, blooming on bare wood in late winter or early spring. The opposite of synanthous. A useful field identification cue during spring bloom.
See also: synanthous
Bark trapped between two stems or between a branch and the trunk in a tight crotch angle. Included bark prevents proper tissue interlocking at the branch union, weakening the attachment and increasing the likelihood of failure under load. A key defect identified during structural pruning and tree risk assessment.
See also: codominant stems
Growth habit where the main stem continues growing indefinitely, producing flowers and fruit over an extended period until frost or disease kills the plant. Requires staking or caging. In the Puget Sound lowlands, indeterminate tomatoes risk losing late-set fruit to fall rain and late blight.
See also: determinate
The pathogen material (spores, bacterial cells, infected tissue) capable of initiating new infection. Fallen leaves, mummified fruit, and overwintering cankers are common inoculum sources. Sanitation practices aim to reduce the inoculum load before the next infection cycle begins.
See also: pathogen , sporulation
A developmental stage of an insect larva between molts. Many pest management decisions depend on targeting a specific instar: early instars are usually more vulnerable to insecticides than later ones. Bronze birch borer larvae, for example, cause the most cambial damage in their later instars.
The section of stem between two adjacent nodes. Internode length reflects growing conditions: long internodes indicate vigorous growth, short internodes indicate stress or the end of the growing season.
See also: node
Yellowing between leaf veins while the veins remain green. Classic symptom of iron or manganese deficiency, most often caused by high soil pH (above 7.0) locking micronutrients in forms roots cannot absorb. Common on calcifuge species planted near concrete foundations or in over-limed beds.
Integrated pest management: a decision-making framework that uses monitoring, action thresholds, cultural practices, biological controls, and targeted chemical applications to manage pests with minimal ecological disruption. IPM does not mean "no spraying"; it means spraying only when monitoring data justifies it.
See also: action threshold , scouting
Iron(III) phosphate (ferric phosphate, FePO₄) used as a stomach poison in slug and snail baits. Approved for organic production (OMRI-listed). Causes slugs to stop feeding; mortality in 3 to 7 days. Commercial products include Sluggo and Escar-Go!. Safe for pets and wildlife at labeled application rates.
See also: molluscicide , metaldehyde
The ability of a systemic fungicide to arrest an infection that has already started, within a narrow window after spore germination. For apple scab, myclobutanil and propiconazole provide 36 to 96 hours of kickback activity after a rain event. Once the window closes, the infection is established and no fungicide will stop it.
See also: protectant fungicide , systemic fungicide
A hydrangea flower head composed of a flat or slightly domed corymb with a central disk of small fertile flowers surrounded by a ring of large showy sterile florets. The "lace" is the fertile center, the "cap" is the outer ring. Lacecap forms are the wild flower form of most hydrangea species; mophead is a cultivated variant where sterile florets have taken over the entire head. Because the fertile central flowers produce nectar and pollen, lacecaps attract pollinators and mopheads do not.
See also: mophead , sterile-floret , corymb
Destructive disease caused by the oomycete Phytophthora infestans, affecting tomato and potato. Thrives in cool, wet conditions (50 to 70°F with high humidity). Capable of killing plants within days under favorable conditions. The primary disease threat to tomatoes in the Puget Sound lowlands.
See also: oomycete
The portion of a growth ring produced during slower summer growth. Characterized by smaller, thick-walled cells that add structural density to the wood. The boundary between one year's latewood and the next year's earlywood creates the visible ring line in cross-sections.
See also: earlywood
The dominant upright stem of a tree that establishes the central axis of growth. Most conifers and many deciduous shade trees develop a single central leader. Competing leaders (codominant stems) create weak branch attachments that are prone to failure. Structural pruning addresses leader selection early in a tree's life.
See also: scaffold branch
The continuous period that free water (rain, dew, irrigation, fog) remains on plant surfaces. Many fungal pathogens require a minimum leaf wetness duration at a specific temperature to germinate spores and infect tissue. For Botrytis cinerea, 4 to 6 hours at 65 to 73°F is sufficient for infection.
See also: conidium , sporulation
The larval form of a crane fly (family Tipulidae). Leatherjackets are gray-brown, wrinkled, legless grubs about 1.5 inches long when fully grown. They feed on grass roots and crowns through winter and early spring, causing the brown patches visible in February and March lawns.
See also: instar
Small opening in bark that permits gas exchange between internal stem tissues and the atmosphere. Lenticels appear as raised dots, lines, or pores on young bark and are especially visible on cherry and birch species.
See also: periderm
A soil texture class with balanced proportions of sand, silt, and clay (roughly 40-27-27 percent by weight). Loam is prized for its ideal balance of drainage, water retention, and nutrient-holding capacity. Loam warms moderately in spring and neither compacts like clay nor drains like pure sand. Agricultural soils like Puyallup Series are loam or silt loam.
See also: soil-texture , silt-loam
Large soil pores (greater than 0.08 mm diameter) that allow rapid water movement and air exchange. Created by root channels, worm burrows, plant root decay, and aggregate structure formed from organic matter. Macropores are essential for drainage in clay soils and for root aeration. Compaction destroys macropores.
See also: micropore , soil-structure , organic-matter
A pest management technique that saturates an area with synthetic pheromone, preventing male moths from locating females for mating. Requires large contiguous acreage (typically five to ten or more acres) to be effective. Not practical for individual home orchards.
See also: pheromone trap , integrated-pest-management
A cyclic tetramer of acetaldehyde used as a molluscicide. Damages the mucus-producing cells of slugs, causing dehydration. Highly toxic to dogs and other vertebrates. Documented secondary poisoning risk to ground beetles that consume poisoned slugs. Banned for garden use in the United Kingdom since March 2022.
See also: molluscicide , iron phosphate , secondary poisoning
Small soil pores (less than 0.08 mm diameter) that hold water against gravity through capillary forces. Clay and organic matter increase micropore space, improving water retention. High microporosity in clay allows it to hold abundant water but also creates drainage problems. Sandy soils have low microporosity and dry quickly.
See also: macropore , soil-texture
Tiny, dark resting structures produced by Verticillium dahliae fungus that persist in soil for years, sometimes indefinitely. Microsclerotia germinate in response to root signals and initiate infection. Once established in soil, microsclerotia cannot be eliminated through cultural practice; they define permanent site risk.
A decision-support chart relating air temperature to the hours of leaf wetness required for apple scab infection. Originally published by Mills in 1944 and revised by MacHardy and Gadoury in 1989, who found ascospores need about three fewer hours than Mills calculated. The table remains the foundational tool for timing fungicide applications against apple scab.
See also: ascospore
A feeding tunnel created by insect larvae between the upper and lower surfaces of a leaf. Leafminers of various species produce characteristic mine shapes (serpentine, blotch, tentiform) that aid identification. Most leafminer damage is cosmetic on established plants.
A pesticide formulated to kill mollusks (slugs and snails). The two major classes in garden use are iron phosphate (stomach poison, OMRI-listed) and metaldehyde (mucus disruptor, toxic to vertebrates). Sodium ferric EDTA is a newer third option.
See also: iron phosphate , metaldehyde
A hydrangea flower head (technically a corymb) composed almost entirely of large, showy sterile florets packed into a round, dense, ball-shaped cluster. The classic bigleaf hydrangea look associated with cultivars like 'Nikko Blue' and the Endless Summer series. Mophead forms are sterile and produce no seed, which is why they do not attract pollinators the way lacecap forms do. Also called hortensia.
See also: lacecap , sterile-floret , corymb
Spots or blotches of different color in the soil profile, typically orange/rust and gray, indicating alternating wet and dry conditions at depth. Mottled subsoils are a diagnostic field sign of poor drainage and seasonal water table fluctuation. The pattern reveals how long the soil remains saturated each year.
See also: drainage-class , perched-water-table
Thread-like network of fungal cells (hyphae) that forms the vegetative body of a fungus. Mycelium penetrates host tissue to extract nutrients and produces reproductive structures including spores. Dormant mycelium in dead plant tissue is one way Botrytis cinerea survives winter.
See also: sclerotium , conidium
Relating to the symbiotic association between plant roots and soil fungi. Mycorrhizal fungi extend the effective root system by threading through soil the roots themselves cannot reach, delivering phosphorus, water, and trace nutrients in exchange for plant sugars. Three main types exist: ectomycorrhizal (ECM, forming an external sheath around root tips), arbuscular mycorrhizal (AMF, penetrating root cells), and ericoid (specialized for plants in the heather family). Roughly 70 percent of plant species depend on AMF; ECM types partner with conifers, oaks, birch, and alder.
See also: ectomycorrhizal , arbuscular-mycorrhizal , ericoid-mycorrhizae , extramatrical-mycelium
To plant bulbs, wildflowers, or other species in informal drifts that multiply and spread with minimal maintenance over multiple years, mimicking the appearance of wild populations. Naturalizing bulbs are typically planted in lawns, meadows, or under deciduous trees where they can complete their foliage cycle undisturbed. Daffodils, crocus, and Camassia naturalize readily in the Puget Sound lowlands.
See also: bulb (true bulb)
Death of plant tissue, typically appearing as brown or black areas on leaves, stems, or roots. Necrotic tissue does not recover. The pattern of necrosis (marginal, interveinal, spotty, or zonal) is a primary diagnostic tool for distinguishing diseases, nutrient deficiencies, and environmental stress.
Stems that grow during the current growing season and set flower buds on that same year's new growth. A shrub that "blooms on new wood" can be pruned hard in late winter or early spring without sacrificing flowers, because the flower buds form on stems that have not yet grown. Examples: smooth hydrangea ('Annabelle', Incrediball), panicle hydrangea (all cultivars), butterfly bush, late-blooming clematis. Compare with old-wood.
The point on a stem where leaves, buds, and lateral branches are attached. Nodes are separated by internodes and are key landmarks for winter twig identification.
See also: internode
A naturally occurring insect virus that causes lethal infections in specific host species. NPV spreads through caterpillar populations when individuals feed in close contact, as tent caterpillars do in their communal tents. Viral outbreaks are the primary driver of tent caterpillar population crashes, reducing numbers by 95% or more over one to three years.
See also: parasitoid , IPM
Stems that grew during the previous growing season and have set flower buds for the following year before winter dormancy. A shrub that "blooms on old wood" forms next year's flower buds this fall, carries them through winter, and opens them the following spring or summer. Pruning old-wood bloomers at the wrong time (summer or fall, after buds are set) removes next year's flowers. Examples: bigleaf and mountain hydrangeas (except remontant cultivars), oakleaf hydrangea, climbing hydrangea, forsythia, lilac, rhododendron. Compare with new-wood.
An organism that behaves like a fungus but is more closely related to algae. Oomycetes include water molds like Phytophthora. Unlike fungi, oomycetes depend absolutely on free water for spore dispersal and infection. They are not controlled by fungicides targeting fungal cell walls.
A thick-walled sexual spore produced by oomycetes through fusion of male and female gametes. Oospores are particularly resistant to desiccation and can persist in soil for years. Phytophthora oospores germinate when soil becomes saturated, producing zoospores that swim through water toward plant roots.
See also: zoospore , chlamydospore , sporulation , inoculum
Variety that reproduces true to type from saved seed, pollinated by wind, insects, or self-pollination. Includes both heirlooms and modern open-pollinated selections.
Decomposed plant and animal material in soil, contributing to its dark color and fertility. Organic matter improves soil structure by creating aggregates, increases macropore space in clay (improving drainage), increases micropore space and water retention in sand, and supports biological activity. Target: 3-6% by weight. The universal soil improvement; timeline is years, not weeks. Also called humus when fully decomposed.
See also: soil-structure , macropore , amendment
A pesticide that kills insect eggs. Horticultural oil applied at the correct timing can act as an ovicide against codling moth eggs on fruit surfaces, though the window is narrow and phytotoxicity risk limits practical use.
A branched flower cluster with flowers borne on secondary branches off a central axis, typically forming an elongated, cone-shaped or pyramidal inflorescence. In hydrangeas, the panicle form defines Hydrangea paniculata ('Limelight', 'Little Lime', 'Quick Fire') and separates it at a glance from the flat-topped corymb forms of smooth, bigleaf, mountain, and oakleaf hydrangeas. In the broader plant world, panicles are also the flower structure of lilacs, astilbes, and many grasses.
An insect whose larvae develop inside or on a host organism, eventually killing it. Unlike a parasite (which does not kill its host) or a predator (which kills immediately), a parasitoid develops slowly at the host's expense before killing it. Parasitoid wasps and flies are among the most important natural enemies of landscape pests including tent caterpillars, scale insects, and aphids.
See also: IPM
Ability to set fruit without pollination. Valuable in cool climates where poor weather reduces pollinator activity during bloom. Oregon State's Legend and Oregon Spring tomato varieties carry this trait.
The production of fruit without pollination or fertilization, resulting in seedless or nearly seedless fruit. Common fig varieties (Ficus carica) produce their breba crop parthenocarpically, which is why they fruit reliably in the Pacific Northwest without the fig wasp (Blastophaga psenes) required for pollination of other fig types.
See also: breba
Asexual reproduction in which females produce viable offspring without mating. Many aphid populations and some root weevil species reproduce by parthenogenesis, allowing females to clone themselves and produce numerous generations rapidly. This reproductive strategy enables pest populations to explode from a single colonizing individual.
An organism that causes disease in a host plant. In the Puget Sound lowlands, the major pathogen groups are fungi (powdery mildew, anthracnose, Phytophthora), bacteria (fire blight, Pseudomonas), and oomycetes (often grouped with fungi but biologically distinct). Viruses are rarely significant in ornamental landscapes here.
See also: inoculum , vector , host range
A zone of saturation above an impermeable layer (such as hardpan or clay), separated from the true groundwater table below. Perched water tables are common on upland soils in the Puget Sound lowlands during winter rains when water accumulates above the glacial hardpan, creating the "drowns in February" drainage pattern characteristic of Alderwood soils.
See also: hardpan , drainage-class
The speed at which water moves downward through soil, typically measured in inches per hour via a field percolation test. Standard decision thresholds: less than 0.5 in/hr indicates poor drainage (water persists too long for most plants); 0.5 to 6 in/hr is acceptable for most landscape plants; more than 8 in/hr means soil drains too fast and will need organic matter and irrigation for moisture retention.
See also: drainage-class , hardpan , perched-water-table
The outer bark system consisting of three layers produced by the cork cambium (phellogen): phellem (dead outer cork) on the outside, phelloderm (living inner cells, sometimes photosynthetic) on the inside, and the phellogen itself. Successive periderms form as a tree ages, creating the fissured or exfoliating bark patterns characteristic of each species.
The cork cambium: a meristematic layer in the bark that produces phellem (dead outer bark) outward and phelloderm (living inner bark) inward. Distinct from the vascular cambium, which produces wood and phloem.
See also: periderm , vascular cambium
The study of recurring biological events and their relationship to climate. In practice, phenology means tracking when plants bloom, when pests emerge, and when diseases activate, then using those observations to time management actions. GDD is the quantitative backbone of phenological tracking.
A monitoring device baited with a synthetic version of an insect's sex pheromone. Male moths fly into the trap, giving the grower a count of pest activity and a biofix date for degree-day models. Delta traps with codlemone lures are the standard for codling moth monitoring.
See also: biofix , growing-degree-days
The vascular tissue that transports sugars and other organic compounds from leaves downward to roots and other growing tissues. Phloem sits just inside the bark, outside the cambium. Girdling damage (from string trimmers, rodents, or circling roots) severs the phloem and starves the root system.
A skin reaction caused by contact with plant sap containing furanocoumarins followed by exposure to sunlight. The affected skin develops redness, blistering, or hyperpigmentation. Common triggers include fig sap (Ficus carica), wild parsnip, and giant hogweed. Wear gloves and long sleeves when pruning figs, especially during the growing season when sap flows freely.
A container sunk flush with the soil surface so that ground-dwelling arthropods fall in as they move across the soil at night. Typically a yogurt cup, plastic cup, or jar, sometimes with a roof to keep rain out. Used to monitor carabids, spiders, and other ground-active invertebrates. For diagnostic use in a garden, a single empty cup left overnight and checked at dawn is enough to confirm whether a carabid community is present and in roughly what genera. Not a pest management tool; a monitoring and inventory tool.
See also: monitoring , scouting , carabidae
A herbicide applied to weeds that have already germinated and are actively growing. Post-emergent products work through foliar contact or systemic uptake. They are the fallback when pre-emergent timing was missed.
See also: pre-emergent
A herbicide applied to soil before weed seeds germinate, creating a chemical barrier that prevents root development in germinating seedlings. Timing is critical: the product must be in place before soil temperatures reach the germination threshold for the target weed. In the Puget Sound lowlands, forsythia bloom is the traditional phenological indicator for crabgrass pre-emergent timing.
See also: post-emergent , phenology
Increase in length of roots and stems produced by apical meristems at shoot tips and root tips. Distinct from secondary growth (increase in girth from the vascular cambium). Primary growth is how roots explore new soil and shoots extend into new canopy space each season.
See also: apical meristem , secondary growth
A fungicide that must be present on the plant surface before a pathogen arrives. Protectants prevent spore germination on contact but have no activity against infections that have already started. Once rain washes the product off or new unprotected growth emerges, coverage is gone. Examples: captan, sulfur, chlorothalonil, copper.
See also: systemic fungicide , kickback activity
A flask-shaped fruiting body produced by certain Ascomycete fungi. In apple scab, pseudothecia develop over winter inside dead leaf litter on the ground and produce ascospores the following spring. Reducing leaf litter through fall sanitation directly reduces the number of pseudothecia and, therefore, the primary inoculum load. Plural: pseudothecia.
See also: ascospore
A regulatory restriction on the movement of host plant materials from an area where an invasive pest has been detected, intended to prevent spread to uninfested areas. Oregon's emerald ash borer quarantine (OAR 603-052-1075) restricts movement of ash, olive, and white fringetree materials from five quarantined counties. Materials covered typically include logs, firewood, nursery stock, chips, mulch, stumps, roots, and branches.
See also: emerald ash borer
The rasping, tongue-like feeding organ of mollusks, bearing rows of tiny teeth. Slugs and snails use the radula to scrape plant tissue, producing the characteristic irregular holes with smooth edges that distinguish mollusk feeding from caterpillar or beetle chewing.
See also: gastropod
Ribbon of parenchyma cells extending radially from the center of a trunk outward toward the bark. Rays transport water and nutrients radially, store starch reserves, contribute to wood strength, and produce antimicrobial compounds during defense. In the CODIT model, ray cells form Wall 3, the lateral barrier limiting sideways spread of decay.
See also: codit , compartmentalization
Specialized wood formed in leaning or asymmetrically loaded stems to counteract gravity. Takes two forms: compression wood (conifers, underside of lean) and tension wood (broadleaf trees, upper side of lean). Identifiable in cross-sections as asymmetric growth rings.
See also: compression wood , tension wood
A plant that blooms more than once in a growing season, typically a first flush on old wood followed by a secondary flush on new wood. In the hydrangea context, remontant (or "reblooming") cultivars carry two sets of flower-bud genetics so that a late-frost loss of old-wood buds does not end the season: the new-wood buds still produce a crop later in summer. The Endless Summer series ('Endless Summer', 'BloomStruck') is the best-known remontant bigleaf hydrangea line; 'Tuff Stuff' and 'Tuff Stuff Ah-Ha' are remontant mountain hydrangea selections. Remontant genetics are insurance against bud loss, not a replacement for proper siting and pruning timing.
A plant's genetic ability to limit or prevent infection by a specific pathogen or damage by a specific pest. Resistance is not immunity: resistant cultivars may still show some symptoms under heavy pressure. In HortGuide profiles, resistance ratings range from highly resistant to highly susceptible.
See also: susceptibility , tolerance , cultivar
A horizontal underground stem that produces roots and shoots at its nodes. Rhizomes allow plants to spread laterally through soil, forming colonies. Wild ginger (Asarum caudatum), inside-out flower (Vancouveria hexandra), and redwood sorrel (Oxalis oregana) all spread by rhizomes.
See also: stolon
The narrow zone of soil immediately surrounding and influenced by plant roots. Characterized by intense microbial activity driven by root exudates, the rhizosphere is where most nutrient exchange between roots, soil, and microorganisms occurs. Mycorrhizal fungi colonize roots within this zone.
See also: mycorrhizal , root flare
Wood anatomy pattern in which large vessels are concentrated in the earlywood (spring growth), with much smaller vessels in the latewood. Creates visible pore-size contrast across each growth ring. Oregon white oak and Oregon ash are ring-porous species common in the Puget Sound lowlands.
See also: diffuse porous , vessel , earlywood
A thimble-shaped mass of cells at the tip of a growing root that protects the apical meristem as the root pushes through soil. Root cap cells are continuously abraded and replaced.
See also: apical meristem , primary growth
The widening base of a tree trunk where it transitions into the root system. The root flare should be visible at the soil surface after planting. Buried root flares (from deep planting or mulch volcanoes) promote bark decay, adventitious rooting, and structural instability.
See also: caliper , adventitious
The root system and lower trunk portion of a grafted plant, selected for vigor, soil adaptation, disease resistance, or size control. In ornamental landscapes, Japanese maples and flowering cherries are commonly grafted onto species rootstocks. Rootstock suckers should be removed promptly.
See also: scion , cultivar , sucker
A severe form of fire blight infection where bacteria reach the graft union and infect the rootstock tissue. Unlike scion blight (which typically kills individual branches), rootstock blight can kill the entire tree, sometimes without obvious canopy symptoms before collapse. Susceptible rootstocks include Malling 9 and Malling 26; resistant options include the Geneva series.
See also: fire-blight , rootstock
A lightweight, permeable fabric spread over plants to protect them from cold, insects, and wind while allowing light and water through. Row covers extend the spring growing season for cool-season crops and exclude pests like flea beetles and squash vine borers without spraying. Standard weights range from frost cloth (0.5 oz) for cold protection to heavyweight (1.5 to 2 oz) for insect exclusion. Remove at flowering for pollinator access.
See also: cool-season crops
An organism that feeds on dead or decaying organic matter rather than living tissue. Botrytis cinerea is both a parasite (infects living plants) and a saprophyte (persists on dead tissue), which is why sanitation, removing dead plant material, is a primary control strategy.
See also: mycelium , sclerotium
The outer band of living xylem in a trunk or branch, actively conducting water and dissolved minerals from roots to canopy. Lighter in color than heartwood. Width varies by species and age; young trees may be entirely sapwood.
A plant disease caused by fungi in the genus Venturia, characterized by raised, rough, corky lesions on fruit and olive-green to black spots on leaves. Apple scab (Venturia inaequalis) is the most common form in the Puget Sound lowlands, affecting all Malus species. The name refers to the scab-like texture of fruit lesions where the skin ruptures over the infection site.
See also: ascospore , pseudothecium , Mills table
A primary structural limb that forms the permanent framework of a tree's canopy. Good scaffold branch selection during structural pruning establishes wide branch angles, adequate vertical spacing, and radial distribution around the trunk.
See also: leader
The upper portion of a grafted plant, selected for its desirable ornamental or fruiting characteristics. The scion is grafted onto the rootstock. Cultivar identity comes from the scion; vigor and adaptability come from the rootstock.
See also: rootstock , cultivar
Hard, dark resting structure produced by certain fungi that allows survival through unfavorable conditions such as winter cold or summer drought. Botrytis sclerotia persist in soil and dead plant debris for months to years, producing spores when conditions turn favorable. Plural: sclerotia.
A dense patch of branched hairs on a bee's abdomen (Megachilidae) or hind legs used for transporting pollen. Distinguished from the corbicula (pollen basket) of honeybees and bumble bees. Mason bees carry pollen on a ventral abdominal scopa, which sheds pollen more freely onto flower surfaces, contributing to their high pollination efficiency.
See also: pollinator
Systematic monitoring of plants for pest and disease activity. Scouting means walking a route on a regular schedule, checking specific plant parts for specific symptoms at specific times of year. It is the data-collection step that makes IPM possible.
See also: IPM , action threshold
Increase in girth of stems and roots produced by the vascular cambium (secondary xylem and secondary phloem) and the cork cambium (periderm). Distinguished from primary growth, which is lengthening from apical meristems.
See also: vascular cambium , apical meristem
The poisoning of a predator or scavenger that consumes prey containing a toxic residue from pesticide application. The classic garden example is metaldehyde slug bait: the slug eats the pellet, dies on the soil surface, and is then scavenged by ground beetles, which accumulate lethal metaldehyde doses through their diet. Iron phosphate slug baits are a common substitute because iron phosphate is not bioavailable to insects the way it is to mollusks, so secondary poisoning of beetles does not occur. The same mechanism applies to rodenticide residues in birds of prey and to neonicotinoid residues in pollen-feeding beneficials.
See also: metaldehyde , iron phosphate , carabidae , pesticide-resistance
A young plant grown from seed in its first weeks after germination, typically while still in a container or propagation flat. Seedlings are tender and require consistent moisture, bright light, and protection from temperature extremes and physical stress until they develop enough leaf area to photosynthesize fully.
See also: hardening off , direct sowing
Requiring two years to complete one generation. Some insects are semivoltine in cooler climates where growing seasons are shorter. Emerald ash borer can be semivoltine in northern or maritime climates, with larvae overwintering in earlier instars and completing development the following season rather than pupating after one year.
See also: univoltine , diapause
The programmed decline and death of plant tissue at the end of its functional life. Leaf senescence in autumn involves nutrient reabsorption before leaf drop. Premature senescence (leaves dropping in July) indicates stress, not normal aging.
See also: dormancy
Fixed in place; unable to move independently. Scale insects are sessile once they settle into their feeding site, cemented to the plant by secreted material. Once settled, they lose mobility and must be managed differently than mobile pest stages.
See also: crawler
A fine-textured soil dominated by silt particles (27-50% silt) with lower sand and moderate clay content. Silt loams have high water-holding capacity but low to moderate permeability. In the Puget Sound lowlands, the valley floor soils Woodinville and Briscot are silt loams, often called "clay" by gardeners despite lacking the shrink-swell properties of true clay. They compact easily when wet and require careful timing for soil work.
See also: soil-texture , loam , vertic-properties
A scale insect (family Coccidae) whose outer covering is the insect's own body wall rather than a separate waxy plate. Soft scales excrete honeydew, which coats foliage and serves as a substrate for sooty mold. Soft scales are larger and more conspicuous than armored scales and typically have one generation per year in Western Washington.
See also: armored scale , honeydew , crawler
A measure of hydrogen ion concentration in the soil solution, on a logarithmic scale from 0 (most acidic) to 14 (most alkaline), with 7 as neutral. Each whole number represents a tenfold difference in acidity. Determines nutrient availability: most essential plant nutrients are most accessible between pH 6.0 and 7.0. Puget Sound native soils typically range from pH 5.0 to 6.0.
The temperature of the soil at seed depth, typically measured 2 to 4 inches below the surface. Soil temperature governs seed germination and seedling root development. In the Puget Sound lowlands, soil temperature lags air temperature by 2 to 3 weeks in spring; waiting for adequate soil warmth prevents seed rot and cold shock.
See also: soil thermometer , direct sowing
A thermometer designed to measure soil temperature at seed depth by inserting a probe 2 to 4 inches into the ground. Soil thermometers are essential for timing spring planting: waiting for soil to reach the target temperature for your crop prevents seed rot and improves germination rates. Inexpensive digital versions are widely available.
See also: soil temperature , direct sowing , phenology
The most specific level of USDA soil classification. A named soil type defined by consistent profile characteristics (texture, structure, color, chemical properties, parent material, and drainage). Every point on the USDA Web Soil Survey corresponds to a specific soil series. The Puget Sound lowlands contain nine primary series: Alderwood, Woodinville, Bellingham, Everett, Puyallup, Seattle, Briscot, Snohomish, and Norma.
See also: Web-Soil-Survey
The arrangement of soil particles into clusters (aggregates or peds) held together by organic matter and biological glues. Unlike texture, structure can be improved through organic matter addition, reduced compaction, and biological activity. Good structure creates macropores for water and air movement.
See also: soil-texture , macropore , organic-matter , bulk-density
The relative proportions of sand, silt, and clay particles in a soil sample, expressed as percentages that always sum to 100%. Sand (>0.05 mm), silt (0.002-0.05 mm), and clay (<0.002 mm) are the three primary particle size classes. Soil texture is a permanent physical property determined by parent material and cannot be changed through management. It determines water-holding capacity, nutrient retention, workability, and warming speed.
See also: soil-structure , loam , silt-loam
A bee species in which each female builds and provisions her own nest independently, without a colony, queen, or worker caste. Approximately 90% of bee species worldwide are solitary. Mason bees (Osmia) and leafcutter bees (Megachile) are solitary cavity nesters common in the Puget Sound region.
See also: cavity nesting , scopa
A plant or portion of a plant that shows a spontaneous genetic mutation, producing different characteristics from the parent. Sports are a common source of new cultivars. Gaultheria shallon 'Cascade Sunrise' (PP34625) originated as a sport with orange-red new growth discovered at a nursery in British Columbia.
The production and release of spores by a fungal pathogen. Environmental conditions (temperature, humidity, leaf wetness duration) control sporulation timing. In the Puget Sound lowlands, the wet springs that favor sporulation are why fungal diseases dominate our disease pressure calendar.
An additive mixed into a spray tank that helps the product spread evenly across leaf surfaces and resist being washed off by rain. Particularly important for biological insecticides like Btk, which break down in sunlight and need maximum leaf contact to be effective.
See also: adjuvant , surfactant
A short, stubby side branch on fruit trees and some ornamentals that produces flower buds year after year. Spur-bearing apple and pear cultivars concentrate their production on these structures. Fire blight frequently enters through infected blossom spurs.
A showy flower unit that lacks functional reproductive parts and produces no seed. Sterile florets are typically enlarged and brightly colored to attract pollinators to the small fertile flowers nearby. In hydrangeas, the showy "flowers" on mopheads and the outer ring of lacecaps are sterile florets; the true fertile flowers are the small structures in the center of a lacecap or the (largely absent) interior of a mophead. Sterile florets persist longer on the plant than fertile flowers because they are not investing energy in seed production.
Fine pale dots scattered across a leaf surface caused by mite or insect feeding that punctures individual leaf cells. Stippling appears as if the leaf was dusted with powder and often precedes more serious damage like defoliation. Mite stippling is a common sign of summer stress and heat damage.
A horizontal stem that grows along the soil surface, producing new plants at its nodes. Stolons differ from rhizomes in growing above ground rather than below it. Beach strawberry (Fragaria chiloensis) spreads by stolons, rooting at each node to build a continuous mat.
See also: rhizome
A shoot arising from the root system or from below the graft union on a grafted plant. Suckers from below the graft are genetically different from the desired cultivar and should be removed at the base. Root suckers from species like black locust and sweetgum can be invasive.
See also: watersprout , rootstock
A substance that reduces the surface tension of water, allowing spray solutions to spread evenly across waxy leaf surfaces instead of beading up and rolling off. Copper fungicide and horticultural oil applications are more effective with proper surfactant use.
See also: adjuvant
A plant's relative vulnerability to a specific pathogen or pest. High susceptibility means the plant is readily infected and shows significant damage. In HortGuide profiles, susceptibility is tracked in a matrix linking each plant to its known threats with severity ratings.
See also: resistance , tolerance
Producing flowers and leaves at the same time. Callery pear (Pyrus calleryana) and hawthorn (Crataegus) are synanthous; most cherries (Prunus) are hysteranthous (flowers before leaves). A useful field identification cue during spring bloom.
See also: hysteranthous
In pesticide use: a product that is absorbed into the plant's vascular system and distributed throughout its tissues, providing internal protection. In pathology: an infection that has spread throughout the plant's vascular system rather than remaining localized. Context determines meaning.
A fungicide absorbed into plant tissue that moves within the plant to protect areas beyond the application site. Systemic fungicides can arrest infections already in progress (kickback activity) but only within a narrow post-infection window. Examples for apple scab include myclobutanil and propiconazole.
See also: protectant fungicide , kickback activity
Reaction wood in broadleaf trees (angiosperms), formed on the upper side of a leaning stem. Pulls the stem back toward vertical using a gelatinous fiber layer (G-layer) in cell walls. Can release stored tension unpredictably when cut.
See also: reaction wood , compression wood
A layer of living and dead stems, roots, and other organic debris that accumulates between the soil surface and the green vegetation of a lawn or groundcover planting. In lawns, excessive thatch (over 0.5 inches) restricts water and air movement. Native groundcovers build a natural thatch layer that suppresses weeds and retains moisture, functioning as a self-mulching system.
A pruning cut that removes an entire branch at its point of origin, either at the trunk or at a parent branch. Thinning cuts reduce canopy density without stimulating the vigorous regrowth that heading cuts produce. The preferred cut type for opening canopy structure and improving air circulation.
See also: heading cut
A plant's ability to sustain pest or disease damage without significant impact on health, growth, or appearance. Tolerance differs from resistance: a tolerant plant still gets infected but handles it well. Mature trees often tolerate defoliation that would stress a young transplant.
See also: resistance , susceptibility
Tapered xylem cell that functions in both water conduction and structural support. The sole water-conducting cell type in gymnosperms (conifers). Narrower and less efficient than vessels but less vulnerable to air embolisms.
A method of delivering systemic pesticide directly into a tree's vascular system through small ports drilled into the trunk. Used when soil-applied systemics are insufficient, particularly for large or stressed trees where root uptake is compromised. Emamectin benzoate delivered by trunk injection is the professional standard for emerald ash borer and bronze birch borer protection. Requires a licensed applicator with specialized equipment.
See also: phloem , systemic fungicide
The metric used by the CougarBlight fire blight infection risk model. TRV accumulates based on hourly temperatures relative to the documented growth rate of Erwinia amylovora. When a wetting event coincides with elevated TRV, infection risk is calculated. Threshold values vary by orchard inoculum history. Not equivalent to GDD; the calculation is specific to CougarBlight.
See also: fire-blight , degree-day
Balloon-like outgrowths of parenchyma cells that push into and plug adjacent xylem vessels. Form naturally during the sapwood-to-heartwood transition and rapidly in response to wounding, limiting the spread of decay fungi through the vascular system. A key mechanism in CODIT compartmentalization.
See also: heartwood , sapwood , compartmentalization
Producing one generation per year. Mason bees (Osmia lignaria) are univoltine: adults emerge in spring, nest for 4-8 weeks, and the next generation develops inside sealed cells through summer, fall, and winter before emerging the following spring. Contrasted with multivoltine organisms that produce multiple generations per year.
See also: voltinism
In botany, a naturally occurring subdivision of a species with consistent distinguishing characteristics: Cornus florida var. rubra (pink flowering dogwood). Distinct from cultivar, which is a human-selected form. In casual use the terms are often conflated, but in HortGuide profiles the distinction matters for taxonomy.
See also: cultivar
The lateral meristem, one cell thick, that produces secondary xylem (wood) inward and secondary phloem outward. All radial growth in trunks, branches, and roots originates from the vascular cambium. Not the same as the cork cambium (phellogen), which produces bark.
See also: cambium , secondary growth , phellogen
An organism that transmits a pathogen from one host to another. Insects are the most common vectors in landscape settings: ants, flies, and wasps spread fire blight bacteria between flowers; bark beetles vector Dutch elm disease fungus. Wind and rain splash are abiotic vectors.
The requirement for a prolonged period of cold exposure before a plant can flower or resume normal growth. Unlike chill hours (which apply broadly to dormancy release), vernalization specifically refers to the cold requirement for flowering in certain species, particularly biennials and some perennials.
See also: chill hours , dormancy
Shrink-swell behavior in clay soils that causes seasonal surface cracking when dry and swelling when wet. Soils with vertic properties contain montmorillonite clays that expand when hydrated and contract when desiccated. In the Puget Sound lowlands, Bellingham Series soil exhibits vertic properties. Management focuses on organic matter to create macropores and avoiding soil work in the narrow moisture window between too wet and too dry.
See also: organic-matter , macropore
Wide, tube-like water-conducting cell found in angiosperm (broadleaf tree) xylem. Vessels are stacked end to end with perforated end walls, forming continuous pipelines. More efficient than tracheids but more vulnerable to cavitation and vascular pathogens.
The number of generations an insect completes per year. Univoltine insects have one generation; bivoltine have two; multivoltine have three or more. Voltinism determines how many treatment windows exist per season and how quickly populations can build.
Vegetables that require warm soil (60 to 75°F) and thrive in summer heat: tomatoes, peppers, squash, beans, cucumbers, melons, basil. Warm-season crops are frost-tender and cannot be planted until after the last frost date; in the Puget Sound lowlands this is typically mid-May. Cold soil and chilly nights stunt growth and rot seeds.
See also: cool-season crops , soil temperature
A vigorous, upright shoot arising from latent buds on a branch or trunk, typically in response to stress, heavy pruning, or topping. Watersprouts have weak attachments and poor branch structure. Their proliferation after topping is one reason topping is destructive.
See also: sucker
A free online mapping tool from USDA NRCS that provides detailed soil maps, surveys, and data for any location in the United States. Users enter an address or click on a map to instantly receive the soil series, texture class, drainage class, depth to restrictive layer, and a complete description of the soil profile. Available at websoilsurvey.nrcs.usda.gov.
See also: soil-series
Lignified, differentiated tissue produced by the vascular cambium in response to wounding. Woundwood forms the ribs that gradually close over a pruning cut or injury. Distinct from callus, which is the undifferentiated tissue that forms first at the wound margin.
See also: callus , compartmentalization , cambium
The vascular tissue that transports water and dissolved minerals from roots upward to the canopy. Xylem forms the wood of the tree. Verticillium wilt and Dutch elm disease block xylem vessels, causing the characteristic wilting and branch death pattern.
A mobile, flagellated spore produced by oomycetes that requires free water to swim. Zoospores are attracted to chemicals released by plant roots and navigate through soil water to find hosts. Unlike fungal spores, zoospores cannot survive desiccation or be carried on wind. The absolute water requirement makes Phytophthora a water-dependent pathogen.
See also: oomycete , oospore , chlamydospore , sporulation
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