Black Cottonwood
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.
Quick Facts
Phenological Calendar
As of April 1, 2026, Puget Sound stations range from 1037.1 to 1147.4 GDD₃₂. Black Cottonwood has reached 'first bloom' (1006 GDD₃₂) and is approaching 'leaf emergence', predicted around Apr 5.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 1, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,147 | 'Leaf emergence' | 'Flower buds visible' | 206 |
| Seattle / UW | 1,139 | 'First bloom' | 'Leaf emergence' | 5 |
| Kent / Auburn | 1,077 | 'First bloom' | 'Leaf emergence' | 67 |
| Olympia / Tumwater | 1,075 | 'First bloom' | 'Leaf emergence' | 69 |
| Bellingham / Whatcom | 1,068 | 'First bloom' | 'Leaf emergence' | 76 |
| Tacoma / Puyallup | 1,043 | 'First bloom' | 'Leaf emergence' | 101 |
| Sequim / Rain Shadow | 1,037 | 'First bloom' | 'Leaf emergence' | 107 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 737 | '' |
| 'Full bloom' BBCH '65' | 894 | '' |
| ● 'First bloom' BBCH '61' NOW | 1006 | '' |
| ○ 'Leaf emergence' BBCH '11' NEXT | 1144 | '' est. Apr 5 (forecast) |
| 'Flower buds visible' BBCH '51' | 1353 | '' est. Apr 17 (forecast) |
GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? GDD₃₂ thresholds from USA National Phenology Network citizen science observations (WA+OR). Season tracker for Kent / Auburn as of Apr 1, 2026. Predicted dates use 16-day weather forecast through Apr 17, 2026, then climate normals.