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Field Brief

April 2026 · HortGuide Station Network · Puget Sound Lowlands

Announcement
What's New at HortGuide

If you have been following HortGuide for a while, you will notice some changes. The site has been rebuilt from the ground up. What started as a blog is now a structured knowledge base: 66 published guides, species profiles for plants, diseases, and pests, and a 7-station weather network spanning the Puget Sound lowlands from Bellingham to Olympia. Every station collects the same data (growing degree days, soil temperature, precipitation, spray windows), and the Field Brief draws on that network to give you a regional picture of where the season stands, not just what is happening in one garden.

This issue is the first under the new format. The newsletter goes out on the first of each month with a weather recap, phenological observations from the field, and a lookahead for what to watch next. Everything is grounded in station data and the knowledge base behind the site. If something here is useful, share it. If something is wrong, tell me.

Weather Report
March in Review

March earned its reputation. The month opened warm, with highs pushing toward 59°F in the first days, enough to get buds moving on early-leafing species. Then winter reminded us it still had keys to the house. A sharp cold snap dropped temperatures to 32°F at the Kent station on the 10th, and March 13 delivered the month's signature weather event: 1.1 inches of rain paired with 1.3 inches of snow in a single day, temperatures barely cracking 36°F. Soil temperatures at 6 cm, which had climbed above 51°F during the warm stretch, crashed back to 37°F.

The back half of March settled into a more familiar pattern: cool mornings, variable afternoons, and enough rain to keep the ground soft. Total precipitation for the month ranged from 3.3 inches in the Sequim rain shadow to 7.4 inches in the Cascade foothills at Issaquah. The south Sound stations (Tacoma, Olympia) saw over 6 inches each.

Spray windows were scarce. Kent managed 11 qualifying days out of 30, but Issaquah logged only 4. If you still had dormant applications on your list heading into mid-March, you were fighting the weather for every opening.

1,048
GDD₃₂ (Kent)
1,190+
Chill Hours
4.81"
March Precip (Kent)
37-51°F
Soil Temp Range
11/30
Spray Days (Kent)
424
March GDD₃₂ Added
Chill Hours
1,190+ cumulative - all common cultivars satisfied
Every stone fruit, blueberry, and apple cultivar commonly planted here has met its chill requirement. Dormancy is over. What happens next depends entirely on warmth.
Station Data
By the Numbers

Station data through March 30, 2026. Sorted by GDD₃₂ (highest first) so you can see where your area sits in the season.

Station GDD₃₂ Soil 6cm Spray Days March Precip
Issaquah 1,116 43.6°F 4/30 7.37"
Seattle 1,112 43.9°F 9/30 4.17"
Olympia 1,049 41.3°F 10/30 6.52"
Kent ★ 1,048 43.6°F 11/30 4.81"
Bellingham 1,041 43.2°F 9/30 6.02"
Tacoma 1,017 42.9°F 8/30 6.12"
Sequim 1,012 38.3°F 8/30 3.27"

The regional spread is only 104 GDD₃₂ top to bottom. Issaquah's Cascade foothills position gives it warmer overnight lows (less radiative cooling than the valley floor), which is why it leads despite not being the sunniest station. Sequim, despite its rain shadow sunshine, runs cool: clear nights mean cold nights.

Phenology
Field Notes: March Phenology

I logged 25 phenological observations across four stations in March. Here are the ones that matter most for timing.

Forsythia Forsythia × intermedia
Full bloom on March 21 near Graham, south of Tacoma, at 911 GDD₃₂. Forsythia bloom is often cited as a crabgrass pre-emergent indicator, but it is an early warning, not a deadline: forsythia blooms around 1-25 GDD while crabgrass does not germinate until 150-200 GDD. If your forsythia is blooming, you have time to get pre-emergent down, but do not wait much longer. Understanding growing degree days →
Yoshino Cherry Prunus × yedoensis
Full bloom in the Kent area on March 21 at approximately 915 GDD₃₂, then five days later in Olympia at the state capitol campus at 988 GDD₃₂. That 73 GDD₃₂ gap between stations for the same species at the same phenological stage is exactly the kind of regional variation this network is built to capture. If you are in the south Sound, your cherry bloom ran nearly a week behind central Puget Sound this year.
Red-flowering Currant Ribes sanguineum
Began blooming around March 16 in Issaquah at approximately 895 GDD₃₂. One of the first significant nectar sources for early pollinators, and its timing is a reliable proxy for mason bee activity. If you are seeing currant bloom in your area, mason bees are likely becoming active. Red-flowering currant 'King Edward VII' →
Callery Pear Pyrus calleryana 'Capital'
First flowers on March 26 in the Kent area at 983 GDD₃₂, with new leaves emerging simultaneously. Pseudomonas blossom blast thrives in cold, wet springs like the one we are having; if a late frost coincides with open flowers, the cold injury gives bacteria an entry point. More on Callery pear →
Flowering Dogwood Cornus florida
Bud swell on March 22 in the Kent area at approximately 930 GDD₃₂, not yet open. Full bloom likely in early to mid April. This is one of the most disease-prone bloom periods: anthracnose moves in during cool, wet weather as flowers open. Anthracnose →
Apple Malus × domestica 'Jonagold'
Visible bud swell on spur wood by March 22 in the Kent area at approximately 930 GDD₃₂. If your apple buds are at a similar stage, the window where fire blight and apple scab become real concerns is approaching. Apple scab → Fire blight →
Lookahead
April: What to Watch For
Flowering dogwood and anthracnose timing
Dogwood was at bud swell in the Kent area in late March. Bloom should arrive in the first half of April, and if we get sustained wet weather during that window, anthracnose pressure will be high. Dogwood anthracnose (Discula destructiva) favors cool temperatures in the 50-57°F range during bud break and early leaf development, with prolonged leaf wetness (12+ hours) driving infection. That describes a typical April week here. Scout for spotted or distorted leaves as flowers open and fade. Anthracnose guide →
Apple scab infection periods
With apple buds swelling and green tissue about to emerge, the first apple scab infection periods of the season are imminent. Scab needs wetting events (rain on leaves for a minimum duration at a given temperature) to infect. April typically delivers plenty. If you grow apples or crabapples and did not apply a dormant fungicide, your first protective spray window is when green tip is visible and rain is in the forecast. Apple scab → Apple variety selection →
Crane fly larval damage peaks now
If your lawn has brown, spongy patches that did not green up with the rest of the turf, you are likely seeing the work of leatherjackets: European crane fly larvae that hatched last September and have been feeding on grass roots all winter. The larvae are at their largest right now, and February through April is when their damage is most visible. They will stop feeding around mid-May and pupate, with adults emerging next fall to start the cycle again. If damage is limited to a few patches, the turf will likely recover on its own once feeding stops. Widespread damage may warrant planning for a fall treatment when the next generation of larvae is small and vulnerable. Crane flies →
Soil temperatures and planting decisions
Soil at 6 cm across the network ended March between 38°F (Sequim) and 44°F (Seattle, Kent, Issaquah). Those numbers determine what you can plant right now and what will waste your money if you rush it.
Safe now (soil 40°F+): Peas, spinach, lettuce, radishes, onion sets, and kale can germinate in soil as cool as 35-40°F. Direct sow these any time. Hardened-off transplants of broccoli, cabbage, and cauliflower can go in too.
Wait for 50°F: Beans, beets, carrots, and potatoes need soil consistently above 50°F for reliable germination. We are not there yet at any station.
Wait for 60°F+: Tomatoes, peppers, squash, cucumbers, and melons need 60°F minimum, with tomatoes preferring 65-70°F. Putting warm-season transplants into 44°F soil does not just slow them down; cold roots cannot absorb nutrients or water efficiently, leaving the plant stressed and vulnerable to disease. The transplant sits, the roots rot, and you replant in June anyway. A soil thermometer at 2-inch depth is worth more than any planting calendar.
New on hortguide.com
From the Site
Apple Varieties That Actually Work Here
Nine varieties rated for scab, fire blight, and mildew resistance in our climate
Crabapple Varieties That Earn Their Space
Ornamental and functional picks, with disease tolerance ratings
Dormant Oil Sprays
If you missed your window, here is what to know for next year
Growing Degree Days
How the 7-station network tracks the season, and how to use it

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