Japanese Tree Lilac
Syringa reticulata
Oleaceae · broadleaf deciduous tree · introduced
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
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 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Japanese Tree Lilac typically reaches 'first bloom' at 2167 GDD₃₂, predicted around May 22.
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 | Pre-season | 'First bloom' | 574 |
| Seattle / UW | 1,554 | Pre-season | 'First bloom' | 613 |
| Kent / Auburn | 1,537 | Pre-season | 'First bloom' | 630 |
| Olympia / Tumwater | 1,505 | Pre-season | 'First bloom' | 663 |
| Bellingham / Whatcom | 1,483 | Pre-season | 'First bloom' | 684 |
| Tacoma / Puyallup | 1,472 | Pre-season | 'First bloom' | 695 |
| Sequim / Rain Shadow | 1,434 | Pre-season | 'First bloom' | 733 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ 'First bloom' BBCH '61' NEXT | 2167 | '' est. May 22 (avg) |
| 'Full bloom' BBCH '65' | 2573 | '' est. Jun 7 (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 23, 2026. Predicted dates use 16-day weather forecast through May 10, 2026, then climate normals.