Black Locust
Full bloomRobinia pseudoacacia
Fabaceae · broadleaf deciduous tree · native
Last updated
Black locust (Robinia pseudoacacia) is a fast-growing deciduous tree in the Fabaceae family native to eastern North America from Pennsylvania to Georgia, west to Iowa, Missouri, and Oklahoma. It reaches 60 ft tall with a 49 ft spread (40 ft at 20 years) and has an erect, multiple-stem form with dark furrowed bark. White drooping flower clusters to 10 inches long are fragrant, and the foliage turns gold-yellow in fall.
Black locust is hardy in zones 4a-8b and prefers full sun with well-drained soil (pH 4.0-8.0) and moderate water, requiring a minimum 36-inch root depth. It is nitrogen-fixing and CaCO3-tolerant with four cultivars in the trade. All parts are toxic except the flowers. Two diseases and three pests are documented; the species has weed and invasive potential.
Quick Facts
Spore Release (Fall & Spring Rains)
Spring Colonization
Overwintering Larvae (Years 2-3)
Phenological Calendar
As of May 14, 2026, Puget Sound stations range from 1926.1 to 2121.1 GDD₃₂. Black Locust has passed full bloom (1835 GDD₃₂).
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 14, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,121 | Full bloom | — | — |
| Kent / Auburn | 2,113 | Full bloom | — | — |
| Seattle / UW | 2,085 | Full bloom | — | — |
| Olympia / Tumwater | 2,047 | Full bloom | — | — |
| Tacoma / Puyallup | 2,016 | Full bloom | — | — |
| Bellingham / Whatcom | 1,994 | Full bloom | — | — |
| Sequim / Rain Shadow | 1,926 | Full bloom | — | — |
| Stage | GDD32 | Typical Window |
|---|---|---|
| Bloom start BBCH 61 | 1566 | Mar 15-May 15 |
| ● Full bloom BBCH 65 NOW | 1835 | — |
| Bud break BBCH 07 | — | Feb 15-Mar 15 |
| Leaf emergence BBCH 11 | — | Mar 1-Apr 1 |
| Bloom end / petal fall BBCH 69 | — | Apr 15-May 31 |
| Fruit/seed development BBCH 71 | — | Mar 15-May 31 |
| Fruit/seed maturity BBCH 85 | — | Jun 1-Aug 31 |
| Leaf drop BBCH 93 | — | Oct 15-Nov 30 |
| Dormancy BBCH 97 | — | Nov 15-Feb 28 |
Sources: USDA Plants Database (seasonal estimate) ; UMD: extension.umd.edu) About GDD₃₂ →
Season tracker for Kent / Auburn as of May 14, 2026. Predicted dates use 16-day weather forecast through May 30, 2026, then climate normals.