Western Ninebark Pacific Ninebark
Physocarpus capitatus
Rosaceae · broadleaf deciduous shrub · native
Last updated
This profile contains verified botanical data. Regional field notes and expert review are in progress.
Physocarpus capitatus (Rosaceae) is a deciduous shrub native to western North America from Alaska to California and east to Idaho and Montana. It grows 6 to 12 feet tall with an arching habit and exfoliating bark that peels in papery strips. Dense, rounded clusters of small white flowers appear in late spring, followed by reddish fruit capsules.
Pacific ninebark grows in full sun to part shade on moist to wet soils. It tolerates seasonal flooding and clay, making it useful for riparian restoration, rain gardens, and wet sites. No significant pest or disease problems are documented. Hardy in Zones 4a to 8b.
Quick Facts
Phenological Calendar
As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Western Ninebark Pacific Ninebark has reached 'flower buds visible' (1334 GDD₃₂) and is approaching 'first bloom', predicted around May 11.
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 | 'Flower buds visible' | 'First bloom' | 363 |
| Seattle / UW | 1,554 | 'Flower buds visible' | 'First bloom' | 402 |
| Kent / Auburn | 1,537 | 'Flower buds visible' | 'First bloom' | 419 |
| Olympia / Tumwater | 1,505 | 'Flower buds visible' | 'First bloom' | 452 |
| Bellingham / Whatcom | 1,483 | 'Flower buds visible' | 'First bloom' | 473 |
| Tacoma / Puyallup | 1,472 | 'Flower buds visible' | 'First bloom' | 484 |
| Sequim / Rain Shadow | 1,434 | 'Flower buds visible' | 'First bloom' | 522 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 661 | '' |
| 'Leaf emergence' BBCH '11' | 859 | '' |
| 'Fall color / leaf senescence' BBCH '93' | 889 | '' |
| ● 'Flower buds visible' BBCH '51' NOW | 1334 | '' |
| ○ 'First bloom' BBCH '61' NEXT | 1956 | '' est. May 11 (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 23, 2026. Predicted dates use 16-day weather forecast through May 9, 2026, then climate normals.