Lewis' Mock Orange
Philadelphus lewisii
Hydrangeaceae · broadleaf deciduous shrub · native
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Philadelphus lewisii (Hydrangeaceae) is a deciduous shrub native to western North America from British Columbia to California and east to Montana. It grows 6 to 10 feet tall with arching branches. Clusters of pure white, four-petaled flowers (1 to 1.5 inches across) appear in late spring to early summer and are intensely fragrant. The species was named for Meriwether Lewis, who collected it during the Lewis and Clark expedition.
Lewis's mockorange grows in full sun to part shade on well-drained soil with moderate moisture. It tolerates dry conditions once established. It blooms on old wood, so pruning should follow flowering. The species is the state flower of Idaho. No significant pest or disease problems are documented. Hardy in Zones 4a to 8b.
Quick Facts
Phenological Calendar
As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Lewis' Mock Orange has reached 'leaf emergence' (983 GDD₃₂) and is approaching 'flower buds visible', predicted around Apr 27.
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' | 'First bloom' | 881 |
| Seattle / UW | 1,554 | 'Leaf emergence' | 'Flower buds visible' | 31 |
| Kent / Auburn | 1,537 | 'Leaf emergence' | 'Flower buds visible' | 48 |
| Olympia / Tumwater | 1,505 | 'Leaf emergence' | 'Flower buds visible' | 81 |
| Bellingham / Whatcom | 1,483 | 'Leaf emergence' | 'Flower buds visible' | 102 |
| Tacoma / Puyallup | 1,472 | 'Leaf emergence' | 'Flower buds visible' | 113 |
| Sequim / Rain Shadow | 1,434 | 'Leaf emergence' | 'Flower buds visible' | 151 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 778 | '' |
| ● 'Leaf emergence' BBCH '11' NOW | 983 | '' |
| ○ 'Flower buds visible' BBCH '51' NEXT | 1585 | '' est. Apr 27 (forecast) |
| 'First bloom' BBCH '61' | 2474 | '' est. Jun 4 (avg) |
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.