Blue Blossom
Ceanothus thyrsiflorus
Rhamnaceae · broadleaf evergreen shrub · native
Last updated
You encounter Blueblossom Ceanothus on coastal scrub and open forest edges from Oregon south to California, recognized by its glossy evergreen foliage and abundant clusters of tiny blue to purple flowers. This native shrub thrives on sandy, rocky slopes where summer dry conditions persist.
Blueblossom grows 4-15 feet tall in full sun with low water needs and excellent drought tolerance once established (zones 8a-9a). It prefers well-drained sandy or gravelly soils; waterlogged conditions trigger root rot. Nitrogen-fixing, it suits poor, eroded sites. Evergreen and relatively pest-free compared to deciduous ceanothus species, though leaf spot and root rot can occur. Prune after flowering to maintain shape; avoid heavy pruning of established plants.
Quick Facts
Phenological Calendar
As of April 12, 2026, Puget Sound stations range from 1235.8 to 1375.3 GDD₃₂. Blue Blossom typically reaches 'flower buds visible' at 1473 GDD₃₂, predicted around Apr 22.
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 | 'Flower buds visible' | 98 |
| Seattle / UW | 1,348 | Pre-season | 'Flower buds visible' | 125 |
| Kent / Auburn | 1,308 | Pre-season | 'Flower buds visible' | 165 |
| Olympia / Tumwater | 1,292 | Pre-season | 'Flower buds visible' | 181 |
| Bellingham / Whatcom | 1,270 | Pre-season | 'Flower buds visible' | 203 |
| Tacoma / Puyallup | 1,258 | Pre-season | 'Flower buds visible' | 215 |
| Sequim / Rain Shadow | 1,236 | Pre-season | 'Flower buds visible' | 237 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ 'Flower buds visible' BBCH '51' NEXT | 1473 | '' est. Apr 22 (forecast) |
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 12, 2026. Predicted dates use 16-day weather forecast through Apr 28, 2026, then climate normals.