Scotch Broom
Cytisus scoparius
Fabaceae · broadleaf deciduous shrub · introduced
Last updated
Data Coverage 4 of 6 dimensions
Quick Facts
Height
4–8 ft
Spread
4–8 ft
Growth Rate
Fast
Light
Full Sun
Soil
Moist
Water
Moderate
Hardiness
Zone Zones 5–6
Bloom Time
May to June
Origin
central and southern Europe
Phenological Calendar
As of April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂. Scotch Broom has reached 'bud break' (1084 GDD₃₂) and is approaching 'flower buds visible', predicted around Apr 13.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,181 | 'Bud break' | 'Flower buds visible' | 123 |
| Seattle / UW | 1,171 | 'Bud break' | 'Flower buds visible' | 133 |
| Kent / Auburn | 1,111 | 'Bud break' | 'Flower buds visible' | 193 |
| Olympia / Tumwater | 1,106 | 'Bud break' | 'Flower buds visible' | 198 |
| Bellingham / Whatcom | 1,101 | 'Bud break' | 'Flower buds visible' | 203 |
| Tacoma / Puyallup | 1,075 | 'Fall color / leaf senescence' | 'Bud break' | 9 |
| Sequim / Rain Shadow | 1,070 | 'Fall color / leaf senescence' | 'Bud break' | 14 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Fall color / leaf senescence' BBCH '93' | 1018 | '' |
| ● 'Bud break' BBCH '07' NOW | 1084 | '' |
| ○ 'Flower buds visible' BBCH '51' NEXT | 1304 | '' est. Apr 13 (forecast) |
| 'Leaf emergence' BBCH '11' | 1337 | '' est. Apr 14 (forecast) |
| 'First bloom' BBCH '61' | 1539 | '' est. Apr 25 (avg) |
Range: 1177–1952 GDD₃₂
(8yr) · 36 obs
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 3, 2026. Predicted dates use 16-day weather forecast through Apr 19, 2026, then climate normals.
Cultivars (1)
'Moonlight'
Common name: Moonlight Scotch Broom