Silk Tree
Albizia julibrissin
Fabaceae · broadleaf deciduous tree · introduced
Last updated
Data Maturity Structured
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Quick Facts
Height
20–30 ft
Spread
32 ft
Growth Rate
Fast
Light
Full Sun
Soil
Wet Tolerant
Water
Moderate
Hardiness
Zone Zones 6a–8b
Bloom Time
June to July
Origin
from Iran to central China
Phenological Calendar
As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Silk Tree typically reaches 'first bloom' at 3165 GDD₃₂, predicted around Jun 26.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 23, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,593 | Pre-season | 'First bloom' | 1,572 |
| Seattle / UW | 1,554 | Pre-season | 'First bloom' | 1,611 |
| Kent / Auburn | 1,537 | Pre-season | 'First bloom' | 1,628 |
| Olympia / Tumwater | 1,505 | Pre-season | 'First bloom' | 1,661 |
| Bellingham / Whatcom | 1,483 | Pre-season | 'First bloom' | 1,682 |
| Tacoma / Puyallup | 1,472 | Pre-season | 'First bloom' | 1,693 |
| Sequim / Rain Shadow | 1,434 | Pre-season | 'First bloom' | 1,731 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ 'First bloom' BBCH '61' NEXT | 3165 | '' est. Jun 26 (avg) |
| 'Full bloom' BBCH '65' | 3665 | '' est. Jul 12 (avg) |
Range: 2711–3098 GDD₃₂
(6yr)
GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? Source GDD₅₀ thresholds from Herms 2004 (OSU, Secrest Arboretum, Ohio) and UMD IPMnet (Gill & Klick, mid-Atlantic), converted to GDD₃₂ via Kent bloom-date mapping. Season tracker for Kent / Auburn as of Apr 23, 2026. Predicted dates use 16-day weather forecast through May 9, 2026, then climate normals.
Cultivars (1)
'Summer Chocolate' Summer Chocolate®
Common name: Summer Chocolate Silk Tree; Mature height: 20 ft
Hardy to USDA Zone 6