Black Cottonwood
'Leaf emergence'Populus trichocarpa
Salicaceae · broadleaf deciduous tree · native
Last updated
Populus trichocarpa (Salicaceae) is a massive deciduous tree native to western North America from Alaska to Baja California, growing primarily along rivers and in bottomlands. It is the tallest broadleaf tree in the region, capable of exceeding 150 feet. The heart-shaped leaves are dark green above and silvery beneath, and the resinous buds are intensely fragrant in spring.
Black cottonwood grows rapidly in full sun on moist to wet soils along rivers and floodplains. It is valued for riparian restoration and shade but is problematic near structures and infrastructure due to invasive roots, brittle wood, and the abundant cotton from female trees. The species is important for wildlife habitat and streambank stabilization. Hardy in Zones 6a to 8b.
Plant Profile
Size & Form
Site Requirements
Ornamental Interest
Field Observations
Peak Spore Production and Dispersal
Active Conidial Spread
Peak Population & Dispersal
Larval Feeding & Web Building
+ 7 more — see full disease and pest lists below
Diseases: Regionally Documented (17)
Pests: Regionally Documented (14)
Phenological Calendar
As of June 3, 2026, Puget Sound stations range from 2435.5 to 2672.8 GDD₃₂. Black Cottonwood has passed 'leaf emergence' (1144 GDD₃₂).
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Jun 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,673 | 'Leaf emergence' | — | — |
| Kent / Auburn | 2,665 | 'Leaf emergence' | — | — |
| Seattle / UW | 2,610 | 'Leaf emergence' | — | — |
| Olympia / Tumwater | 2,570 | 'Leaf emergence' | — | — |
| Tacoma / Puyallup | 2,535 | 'Leaf emergence' | — | — |
| Bellingham / Whatcom | 2,533 | 'Leaf emergence' | — | — |
| Sequim / Rain Shadow | 2,436 | 'Leaf emergence' | — | — |
View full calendar (6 stages)
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 737 | 'Feb-Mar' |
| 'Flower buds visible' BBCH '51' | — | 'Feb-Mar' |
| 'First bloom' BBCH '61' | 1006 | 'Mar-Apr' |
| 'Full bloom / pollen release' BBCH '65' | 894 | 'Mar-May' |
| ● 'Leaf emergence' BBCH '11' NOW | 1144 | 'Apr-May' |
| 'Seed dispersal' BBCH '85' | — Observed | 'May' |
Source: 'NPN citizen science observations (WA+OR), n=5, median (pollen_release phase). Low confidence due to small sample. services.usanpn.org' About GDD₃₂ →
Season tracker for Kent / Auburn as of Jun 3, 2026. Predicted dates use 16-day weather forecast through Jun 19, 2026, then climate normals.