Northern Lights Forsythia
Forsythia x intermedia
Oleaceae · [VERIFY] · introduced
Last updated
Deciduous shrub growing 6 to 8 feet tall with bright yellow four-lobed flowers covering arching stems in early spring before leaf emergence. Foliage is medium green; form is loose and spreading.
Hardy, low-maintenance spring accent shrub thriving in full sun to light shade and adaptable soils. Prune after flowering to shape; old canes can be removed at the base. No significant pests or diseases; tends toward leggy growth without selective pruning.
Quick Facts
Phenological Calendar
As of April 19, 2026, Puget Sound stations range from 1342.9 to 1500.8 GDD₃₂. Northern Lights Forsythia has passed full bloom (686 GDD₃₂).
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 19, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,501 | Full bloom | — | — |
| Seattle / UW | 1,465 | Full bloom | — | — |
| Kent / Auburn | 1,441 | Full bloom | — | — |
| Olympia / Tumwater | 1,415 | Full bloom | — | — |
| Bellingham / Whatcom | 1,390 | Full bloom | — | — |
| Tacoma / Puyallup | 1,381 | Full bloom | — | — |
| Sequim / Rain Shadow | 1,343 | Full bloom | — | — |
| Stage | GDD32 | Typical Window |
|---|---|---|
| Beginning of flowering 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 19, 2026. Predicted dates use 16-day weather forecast through May 5, 2026, then climate normals.