Blue Blossom
Ceanothus thyrsiflorus
Rhamnaceae · broadleaf evergreen shrub · native
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
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 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Blue Blossom has passed 'flower buds visible' (1473 GDD₃₂).
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' | — | — |
| Seattle / UW | 1,554 | 'Flower buds visible' | — | — |
| Kent / Auburn | 1,537 | 'Flower buds visible' | — | — |
| Olympia / Tumwater | 1,505 | 'Flower buds visible' | — | — |
| Bellingham / Whatcom | 1,483 | 'Flower buds visible' | — | — |
| Tacoma / Puyallup | 1,472 | Pre-season | 'Flower buds visible' | 1 |
| Sequim / Rain Shadow | 1,434 | Pre-season | 'Flower buds visible' | 39 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ● 'Flower buds visible' BBCH '51' NOW | 1473 | '' |
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 10, 2026, then climate normals.