Butterfly bush
Buddleia hemsleyana
Scrophulariaceae · [VERIFY] · introduced
Last updated
Semi-woody deciduous shrub with narrow, lance-shaped foliage and terminal panicles of small tubular flowers in late summer and fall. Flowers range from white to pale lilac and are highly fragrant, attracting butterflies and pollinators.
Requires warm, sheltered sites and full sun. Prefers well-drained soil; drought tolerant when established. Less aggressive than B. davidii; treated as herbaceous perennial in cooler climates. Prune hard in late winter for vigor.
Quick Facts
Phenological Calendar
As of April 19, 2026, Puget Sound stations range from 1342.9 to 1500.8 GDD₃₂. Butterfly bush typically reaches beginning of flowering at 3352 GDD₃₂, predicted around Jul 2.
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 | Pre-season | Beginning of flowering | 1,851 |
| Seattle / UW | 1,465 | Pre-season | Beginning of flowering | 1,887 |
| Kent / Auburn | 1,441 | Pre-season | Beginning of flowering | 1,911 |
| Olympia / Tumwater | 1,415 | Pre-season | Beginning of flowering | 1,937 |
| Bellingham / Whatcom | 1,390 | Pre-season | Beginning of flowering | 1,962 |
| Tacoma / Puyallup | 1,381 | Pre-season | Beginning of flowering | 1,972 |
| Sequim / Rain Shadow | 1,343 | Pre-season | Beginning of flowering | 2,009 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ Beginning of flowering BBCH 61 NEXT | 3352 | — est. Jul 2 (avg) |
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.