Japanese Tree Lilac
Syringa reticulata
Oleaceae · broadleaf deciduous tree · introduced
Last updated
Japanese tree lilac, also called giant tree lilac, is a deciduous tree native to Japan, reaching 30-50 feet tall with a single stem or multi-stemmed form. The tree produces white, slightly fragrant flowers in large, pyramidal panicles in early to midsummer and has glossy, dark green leaves with fine bronze-red fall color.
Japanese tree lilac is hardy to zones 3-7 and thrives in full sun to light shade with well-drained soil. It blooms later than common lilac (June-July) and is less susceptible to mildew and scale. The tree is long-lived and low-maintenance once established; multiple cultivars are available.
Quick Facts
Phenological Calendar
As of April 3, 2026, Puget Sound stations range from 1070 to 1180.6 GDD₃₂. Japanese Tree Lilac typically reaches 'first bloom' at 2167 GDD₃₂, predicted around May 23.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 3, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,181 | Pre-season | 'First bloom' | 986 |
| Seattle / UW | 1,171 | Pre-season | 'First bloom' | 996 |
| Kent / Auburn | 1,111 | Pre-season | 'First bloom' | 1,056 |
| Olympia / Tumwater | 1,106 | Pre-season | 'First bloom' | 1,061 |
| Bellingham / Whatcom | 1,101 | Pre-season | 'First bloom' | 1,066 |
| Tacoma / Puyallup | 1,075 | Pre-season | 'First bloom' | 1,092 |
| Sequim / Rain Shadow | 1,070 | Pre-season | 'First bloom' | 1,097 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ 'First bloom' BBCH '61' NEXT | 2167 | '' est. May 23 (avg) |
| 'Full bloom' BBCH '65' | 2573 | '' est. Jun 8 (avg) |
GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? Hover over GDD values for source details. Season tracker for Kent / Auburn as of Apr 3, 2026. Predicted dates use 16-day weather forecast through Apr 19, 2026, then climate normals.