Western Ninebark Pacific Ninebark
Physocarpus capitatus
Rosaceae · broadleaf deciduous shrub · native
Last updated
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
Spring Emergence / Primary Infection
Phenological Calendar
As of May 13, 2026, Puget Sound stations range from 1906.2 to 2098.2 GDD₃₂. Western Ninebark Pacific Ninebark has passed 'first bloom' (1956 GDD₃₂).
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 13, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,098 | 'First bloom' | — | — |
| Kent / Auburn | 2,089 | 'First bloom' | — | — |
| Seattle / UW | 2,063 | 'First bloom' | — | — |
| Olympia / Tumwater | 2,025 | 'First bloom' | — | — |
| Tacoma / Puyallup | 1,993 | 'First bloom' | — | — |
| Bellingham / Whatcom | 1,972 | 'First bloom' | — | — |
| Sequim / Rain Shadow | 1,906 | 'Flower buds visible' | 'First bloom' | 50 |
| 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' | 1334 | '' |
| ● 'First bloom' BBCH '61' NOW | 1956 | '' |
Source: 'NPN citizen science observations (WA+OR), n=60, median. services.usanpn.org' About GDD₃₂ →
Season tracker for Kent / Auburn as of May 13, 2026. Predicted dates use 16-day weather forecast through May 29, 2026, then climate normals.