Cascara Cascara Buckthorn
Rhamnus purshiana
Rhamnaceae · broadleaf deciduous tree · native
Last updated
Cascara buckthorn (Rhamnus purshiana) is a deciduous shrub or small tree in the Rhamnaceae family native to western North America. It reaches 32 ft tall with a 19 ft spread, growing in rich bottomlands and coniferous forest habitats. The bark has historically been harvested for its laxative properties.
Cascara tolerates sun to part shade and prefers moist soil with a broad pH tolerance of 4.5-8.5. One disease is documented in managed landscapes. All parts may cause skin irritation on contact. The plant provides wildlife food and is valued for its ecological role in forest understory communities.
Quick Facts
Phenological Calendar
As of April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂. Cascara Cascara Buckthorn has reached 'leaf emergence' (981 GDD₃₂) and is approaching 'first bloom', predicted around Apr 29.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,181 | 'Leaf emergence' | 'First bloom' | 432 |
| Seattle / UW | 1,171 | 'Leaf emergence' | 'First bloom' | 442 |
| Kent / Auburn | 1,111 | 'Leaf emergence' | 'First bloom' | 502 |
| Olympia / Tumwater | 1,106 | 'Leaf emergence' | 'First bloom' | 507 |
| Bellingham / Whatcom | 1,101 | 'Leaf emergence' | 'First bloom' | 512 |
| Tacoma / Puyallup | 1,075 | 'Leaf emergence' | 'First bloom' | 538 |
| Sequim / Rain Shadow | 1,070 | 'Leaf emergence' | 'First bloom' | 543 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 856 | '' |
| ● 'Leaf emergence' BBCH '11' NOW | 981 | '' |
| ○ 'First bloom' BBCH '61' NEXT | 1613 | '' est. Apr 29 (avg) |
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 3, 2026. Predicted dates use 16-day weather forecast through Apr 19, 2026, then climate normals.