Common Lilac
Syringa vulgaris
Oleaceae · broadleaf deciduous shrub · introduced
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Common lilac is the one shrub that wants the opposite of what the Puget Sound lowlands naturally provide. It prefers alkaline soil (ours is acidic), dry summers (ours has drought but preceded by eight months of rain), and good air circulation (ours has persistent spring humidity). The result is chronic powdery mildew and bacterial blight, especially in wet springs. Despite all this, lilacs persist here because they are tough and people love them. The keys to success: full sun, no overhead irrigation, thin the interior for airflow, and lime the soil periodically to push pH toward neutral. Bloom happens on old wood; prune immediately after flowering in May. Lilac borer and oystershell scale are the pests that cause real damage. Sucker management is a recurring chore. For the effort involved, the two weeks of fragrant bloom in May are either worth it or they are not.
— Chris Welch, ISA Certified Arborist
Common lilac is a deciduous shrub native to the Balkans, reaching 8-15 feet tall with a spreading, multi-stemmed form. The plant produces highly fragrant flowers in terminal panicles ranging from white to dark purple, blooming in late spring. The foliage is heart-shaped and dark green.
Common lilac is extremely cold-hardy to zones 2-8 and thrives in full sun with well-drained soil. It is fast-growing and long-lived; hundreds of cultivars are available with selections for flower color, bloom time, and growth habit. The plant is susceptible to mildew in humid conditions; pruning immediately after flowering maintains vigor.
Quick Facts
Phenological Calendar
As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂. Common Lilac has passed 'first bloom' (1302 GDD₃₂).
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 | 'First bloom' | — | — |
| Seattle / UW | 1,554 | 'First bloom' | — | — |
| Kent / Auburn | 1,537 | 'First bloom' | — | — |
| Olympia / Tumwater | 1,505 | 'First bloom' | — | — |
| Bellingham / Whatcom | 1,483 | 'First bloom' | — | — |
| Tacoma / Puyallup | 1,472 | 'First bloom' | — | — |
| Sequim / Rain Shadow | 1,434 | 'First bloom' | — | — |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 716 | '' |
| ● 'First bloom' BBCH '61' NOW | 1302 | '' |
| Flower bud development BBCH 55 | — | — |
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.