Lewis' Mock Orange
'First bloom'Philadelphus lewisii
Hydrangeaceae · broadleaf deciduous shrub · native
Last updated
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.
Plant Profile
Size & Form
Site Requirements
Ornamental Interest
Diseases: Regionally Documented (1)
Phenological Calendar
As of June 3, 2026, Puget Sound stations range from 2435.5 to 2672.8 GDD₃₂. Lewis' Mock Orange has passed 'first bloom' (2474 GDD₃₂).
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Jun 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,673 | 'First bloom' | — | — |
| Kent / Auburn | 2,665 | 'First bloom' | — | — |
| Seattle / UW | 2,610 | 'First bloom' | — | — |
| Olympia / Tumwater | 2,570 | 'First bloom' | — | — |
| Tacoma / Puyallup | 2,535 | 'First bloom' | — | — |
| Bellingham / Whatcom | 2,533 | 'First bloom' | — | — |
| Sequim / Rain Shadow | 2,436 | 'Flower buds visible' | 'First bloom' | 39 |
View full calendar (4 stages)
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 778 | '' |
| 'Leaf emergence' BBCH '11' | 983 | '' |
| 'Flower buds visible' BBCH '51' | 1585 | '' |
| ● 'First bloom' BBCH '61' NOW | 2474 | '' |
Source: 'NPN citizen science observations (WA+OR), n=39, median. services.usanpn.org' About GDD₃₂ →
Season tracker for Kent / Auburn as of Jun 3, 2026. Predicted dates use 16-day weather forecast through Jun 19, 2026, then climate normals.