Field Horsetail

Equisetum arvense

Equisetaceae · fern ally · native

Last updated

Quick Facts

Height
1-2 ft (vegetative shoots; LBJWC reports up to 3 ft on optimal sites)
Spread
indefinite (rhizomatous; rhizome systems documented to 330 ft horizontally and 20 ft deep)
Growth Rate
Fast (vegetative shoots emerge and reach mature height within weeks of spring soil-warming; rhizome expansion is steady year-round in pnw)
Light
Full sun to full shade (LBJWC lists Sun, Part Shade, Shade); most aggressive growth in full sun on moist sites
Soil
Moist to wet; tolerates poor drainage and seasonally waterlogged conditions; wetland indicator (FAC) in all U.S. regions
Water
Moderate to high (lbjwc: water use 'high')
Hardiness
Zones 2–11
Bloom Time
N/A (non-flowering); fertile cone-bearing shoots emerge late March to early May in Puget Sound, before vegetative shoots
Fall Color
Yellow-brown senescence in late autumn before aboveground dieback; rhizomes remain dormant through winter
Origin
Circumboreal; native throughout North America (47 U.S.

Field Observations

Equisetum arvense - new growth
Field Observation
Equisetum arvense · Field Horsetail
new growth
April 25, 2026 · Soos Creek Botanical Garden · 1,580 GDD₃₂ · BBCH 11

Phenological Calendar

As of May 18, 2026, Puget Sound stations range from 2022.7 to 2224.5 GDD₃₂. Field Horsetail has passed new growth (1580 GDD₃₂).

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of May 18, 2026
Station GDD₃₂ Current Stage Next To Go
Issaquah / East King 2,225 new growth — —
Kent / Auburn 2,194 new growth — —
Seattle / UW 2,164 new growth — —
Olympia / Tumwater 2,128 new growth — —
Bellingham / Whatcom 2,098 new growth — —
Tacoma / Puyallup 2,092 new growth — —
Sequim / Rain Shadow 2,023 new growth — —
Stage GDD32 Typical Window
● new growth BBCH 11 NOW 1580 April-May

Source: Field observation, Auburn WA. About GDD₃₂ →

Season tracker for Kent / Auburn as of May 18, 2026. Predicted dates use 16-day weather forecast through Jun 3, 2026, then climate normals.

Extremely common in Puget Sound lowland landscapes, particularly on Green River valley clay, kettle-pond margins, ditch banks, and any site with compacted or seasonally waterlogged soil. The species' presence is a reliable diagnostic for poor drainage and is more useful as an indicator than as a focal organism. Fertile strobilus-bearing shoots are typically the first thing to push above bare soil in late March, often 2-4 weeks before vegetative shoots — a useful phenological marker that GDD32 has crossed roughly 1,500 in this region. Field observed at Soos Creek Botanical Garden (Auburn, WA) on 2026-04-25 with vegetative shoots fully expanded at 1,580 GDD32 at the Kent station. Eradication in landscape settings is impractical once the rhizome system is established; cultural controls focus on improving drainage and outshading. Glyphosate has reduced efficacy on Equisetum due to the silica-rich cuticle and deep rhizome reservoir.

— Chris Welch, ISA Certified Arborist

Data Maturity
Baseline Extension data. Expert review underway.