Trailing Blackberry Western Blackberry California Blackberry Dewberry
Rubus ursinus
Rosaceae · vine groundcover · native
Last updated
This profile synthesizes data from multiple published sources. Expert field review is in progress.
Trailing blackberry (Rubus ursinus), also called western blackberry, California blackberry, or dewberry, is a broadleaf shrub in the Rosaceae family native to western North America from British Columbia to California, east to Idaho, south to Mexico. It reaches 10-20 ft in length with a trailing habit, forming sprawling thickets in waste places, fields, and canyons below 1,000 meters.
Trailing blackberry is hardy in zones 3a-8b and tolerates full sun to shade with moist soil (pH 4.5-8.5) and moderate water. Thirty-two diseases and 4 pests are documented. The fruit has a moderate edibility rating (3/5). This is the parent species of the cultivated marionberry and other trailing blackberry cultivars.
Quick Facts
Phenological Calendar
As of April 24, 2026, Puget Sound stations range from 1455.1 to 1613.4 GDD₃₂. Trailing Blackberry Western Blackberry California Blackberry Dewberry has reached 'flower buds visible' (1405 GDD₃₂) and is approaching 'first bloom', predicted around Apr 27.
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 | 'First bloom' | — | — |
| Seattle / UW | 1,574 | 'Flower buds visible' | 'First bloom' | 38 |
| Kent / Auburn | 1,559 | 'Flower buds visible' | 'First bloom' | 53 |
| Olympia / Tumwater | 1,524 | 'Flower buds visible' | 'First bloom' | 89 |
| Bellingham / Whatcom | 1,504 | 'Flower buds visible' | 'First bloom' | 108 |
| Tacoma / Puyallup | 1,492 | 'Flower buds visible' | 'First bloom' | 120 |
| Sequim / Rain Shadow | 1,455 | 'Flower buds visible' | 'First bloom' | 157 |
| Stage | GDD32 | Typical Window |
|---|---|---|
| 'Bud break' BBCH '07' | 842 | '' |
| 'Leaf emergence' BBCH '11' | 953 | '' |
| 'Fall color / leaf senescence' BBCH '93' | 1173 | '' |
| ● 'Flower buds visible' BBCH '51' NOW | 1405 | '' |
| ○ 'First bloom' BBCH '61' NEXT | 1612 | '' est. Apr 27 (forecast) |
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 24, 2026. Predicted dates use 16-day weather forecast through May 10, 2026, then climate normals.