Winterberrry Winterberry Holly
Ilex verticillata
Aquifoliaceae · broadleaf deciduous shrub · native
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Quick Facts
Phenological Calendar
As of April 24, 2026, Puget Sound stations range from 1455.1 to 1613.4 GDD₃₂. Winterberrry Winterberry Holly typically reaches bloom start at 2700 GDD₃₂, predicted around Jun 10.
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 24, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 1,613 | Pre-season | Bloom start | 1,087 |
| Seattle / UW | 1,574 | Pre-season | Bloom start | 1,126 |
| Kent / Auburn | 1,559 | Pre-season | Bloom start | 1,141 |
| Olympia / Tumwater | 1,524 | Pre-season | Bloom start | 1,177 |
| Bellingham / Whatcom | 1,504 | Pre-season | Bloom start | 1,196 |
| Tacoma / Puyallup | 1,492 | Pre-season | Bloom start | 1,208 |
| Sequim / Rain Shadow | 1,455 | Pre-season | Bloom start | 1,245 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ○ Bloom start BBCH 61 NEXT | 2700 | May 1-May 31 est. Jun 10 (avg) |
| Full bloom BBCH 65 | 3050 | — est. Jun 23 (avg) |
| Bud break BBCH 07 | — | Feb 15-Mar 15 |
| Leaf emergence BBCH 11 | — | Mar 1-Apr 1 |
| Bloom end / petal fall BBCH 69 | — | May 15-Jun 15 |
| Fruit/seed development BBCH 71 | — | Jun 1-Aug 31 |
| Fruit/seed maturity BBCH 85 | — | Sep 1-Nov 30 |
| Fall color / leaf senescence BBCH 93 | — | Oct 1-Nov 15 |
| Dormancy BBCH 97 | — | Nov 15-Feb 28 |
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 24, 2026. Predicted dates use 16-day weather forecast through May 10, 2026, then climate normals.