Nippon Spirea
Spiraea nipponica
Rosaceae · broadleaf deciduous shrub · introduced
Last updated
Nippon spirea is a deciduous shrub native to Japan, reaching 4-6 feet tall and wide with small, obovate leaves. The plant produces abundant white flowers in large, flat clusters along arching branches in late spring to early summer.
Nippon spirea is hardy to zones 4-8 and thrives in full sun to light shade with well-drained soil and moderate moisture. It is fast-growing and responds well to pruning immediately after flowering. The cultivar 'Snowmound' is more compact and is widely available.
Quick Facts
Phenological Calendar
As of April 12, 2026, Puget Sound stations range from 1235.8 to 1375.3 GDD₃₂. Nippon Spirea typically reaches 'first bloom' at 1490 GDD₃₂, predicted around Apr 23.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 12, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,375 | Pre-season | 'First bloom' | 115 |
| Seattle / UW | 1,348 | Pre-season | 'First bloom' | 142 |
| Kent / Auburn | 1,308 | Pre-season | 'First bloom' | 182 |
| Olympia / Tumwater | 1,292 | Pre-season | 'First bloom' | 198 |
| Bellingham / Whatcom | 1,270 | Pre-season | 'First bloom' | 220 |
| Tacoma / Puyallup | 1,258 | Pre-season | 'First bloom' | 232 |
| Sequim / Rain Shadow | 1,236 | Pre-season | 'First bloom' | 254 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ 'First bloom' BBCH '61' NEXT | 1490 | '' est. Apr 23 (forecast) |
| 'Full bloom' BBCH '65' | 1815 | '' est. May 7 (avg) |
GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? Hover over GDD values for source details. Season tracker for Kent / Auburn as of Apr 12, 2026. Predicted dates use 16-day weather forecast through Apr 28, 2026, then climate normals.