Showy Forsythia
Forsythia ×intermedia
Oleaceae · broadleaf deciduous shrub · introduced
Last updated
This profile contains verified botanical data. Regional field notes and expert review are in progress.
Showy forsythia (Forsythia × intermedia, Oleaceae) is a fast-growing deciduous shrub of hybrid origin (eastern Asian parentage), reaching 8 to 10 feet tall and 10 to 12 feet wide with upright, arching branches. Pale to deep yellow, four-lobed flowers (3 to 4 centimeters) cover the bare branches in early spring before leaves emerge. It is a key phenological indicator plant: bloom timing correlates with crabgrass pre-emergent application windows and pest emergence thresholds.
Showy forsythia grows in full sun on adaptable soils with moderate water needs, hardy in Zones 4a to 8b. It blooms on old wood; prune immediately after flowering. Documented diseases include bacterial blight, stem gall, and virus; root weevil is an occasional pest. OSU notes cultivars including 'Lynwood Gold,' 'Spectabilis,' and 'Spring Glory.'
Quick Facts
Phenological Calendar
As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Showy Forsythia has passed 'full bloom' (686 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 | 'Full bloom' | — | — |
| Seattle / UW | 1,554 | 'Full bloom' | — | — |
| Kent / Auburn | 1,537 | 'Full bloom' | — | — |
| Olympia / Tumwater | 1,505 | 'Full bloom' | — | — |
| Bellingham / Whatcom | 1,483 | 'Full bloom' | — | — |
| Tacoma / Puyallup | 1,472 | 'Full bloom' | — | — |
| Sequim / Rain Shadow | 1,434 | 'Full bloom' | — | — |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'First bloom' BBCH '61' | 423 | '' |
| ● 'Full bloom' BBCH '65' NOW | 686 | '' |
GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? Source GDD₅₀ thresholds from Herms 2004 (OSU, Secrest Arboretum, Ohio) and UMD IPMnet (Gill & Klick, mid-Atlantic), converted to GDD₃₂ via Kent bloom-date mapping. Season tracker for Kent / Auburn as of Apr 23, 2026. Predicted dates use 16-day weather forecast through May 9, 2026, then climate normals.