Rose
Hibiscus syriacus
Malvaceae · broadleaf deciduous shrub · introduced
Last updated
Rose of Sharon (Hibiscus syriacus, Malvaceae) is an erect, vase-shaped deciduous shrub from China and India (not Syria, despite the misleading epithet), reaching 8 to 12 feet tall and 6 feet wide. Large, trumpet-shaped, five-petaled flowers in blue, lavender, pink, purple, red, and white tones bloom prolifically from July through October. Each flower is short-lived (one day) but the display is continuous on current-season growth.
Rose of Sharon grows in full sun to part shade on moist, well-drained soil (pH 4.5 to 8.5), hardy in Zones 5a to 8b. It tolerates deer browse, drought, clay soil, and black walnut proximity. It blooms on new wood; prune in late winter to early spring. Disease pressure is notable, with 11 documented associations including powdery mildew, crown gall, and rust. Pest pressure is among the highest in the knowledge base: 27 documented associations including aphids, thrips, and fall webworm.
Quick Facts
Phenological Calendar
As of April 12, 2026, Puget Sound stations range from 1235.8 to 1375.3 GDD₃₂. Rose typically reaches beginning of flowering at 3976 GDD₃₂, predicted around Jul 22.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 12, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,375 | Pre-season | Beginning of flowering | 2,601 |
| Seattle / UW | 1,348 | Pre-season | Beginning of flowering | 2,628 |
| Kent / Auburn | 1,308 | Pre-season | Beginning of flowering | 2,668 |
| Olympia / Tumwater | 1,292 | Pre-season | Beginning of flowering | 2,684 |
| Bellingham / Whatcom | 1,270 | Pre-season | Beginning of flowering | 2,706 |
| Tacoma / Puyallup | 1,258 | Pre-season | Beginning of flowering | 2,718 |
| Sequim / Rain Shadow | 1,236 | Pre-season | Beginning of flowering | 2,740 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ Beginning of flowering BBCH 61 NEXT | 3976 | — est. Jul 22 (avg) |
GDD = Growing Degree Days (base 32°F, Jan 1 start). Why base 32? Source GDD₅₀ thresholds from Herms 2004 (OSU, Secrest Arboretum, Ohio) and UMD IPMnet (Gill & Klick, mid-Atlantic), converted to GDD₃₂ via Kent bloom-date mapping. Season tracker for Kent / Auburn as of Apr 12, 2026. Predicted dates use 16-day weather forecast through Apr 28, 2026, then climate normals.