Horse Chestnut
Beginning of floweringAesculus hippocastanum
Sapindaceae · broadleaf deciduous tree · introduced
Last updated
Quick Facts
Spring Emergence / Primary Infection
Phenological Calendar
As of May 13, 2026, Puget Sound stations range from 1906.2 to 2098.2 GDD₃₂. Horse Chestnut has passed beginning of flowering (1130 GDD₃₂).
Regional Season Tracker
GDD₃₂ accumulation across 7 Puget Sound stations · as of May 13, 2026| Station | GDD₃₂ | Current Stage | Next | To Go |
|---|---|---|---|---|
| Issaquah / East King | 2,098 | Beginning of flowering | — | — |
| Kent / Auburn | 2,089 | Beginning of flowering | — | — |
| Seattle / UW | 2,063 | Beginning of flowering | — | — |
| Olympia / Tumwater | 2,025 | Beginning of flowering | — | — |
| Tacoma / Puyallup | 1,993 | Beginning of flowering | — | — |
| Bellingham / Whatcom | 1,972 | Beginning of flowering | — | — |
| Sequim / Rain Shadow | 1,906 | Beginning of flowering | — | — |
| Stage | GDD32 | Typical Window |
|---|---|---|
| ● Beginning of flowering BBCH 61 NOW | 1130 | — |
Source: OSU phenology catalog (OSU: weather.cfaes.osu.edu) About GDD₃₂ →
Season tracker for Kent / Auburn as of May 13, 2026. Predicted dates use 16-day weather forecast through May 29, 2026, then climate normals.
Diseases: Regionally Documented (2)
Cultivars (1)
Horse chestnut produces a dramatic spring flower display and then spends the rest of summer looking increasingly rough. Leaf blotch (Guignardia) turns foliage brown from midsummer onward in most years, and leaf scorch adds to the problem in hot Augusts. Neither condition threatens the tree but both make it look terrible from July through leaf drop. The tree needs moisture; our summer drought stresses it. Bloom happens early (251 GDD base 50, typically May), and the flowers are showy. The seeds contain saponins and are toxic to humans and most animals, which is a serious consideration where children play. 'Baumannii' produces double flowers and few seeds, which addresses the toxicity concern. For a large shade tree with spring flowers and minimal pest issues, horse chestnut works if you can tolerate the late-summer foliage decline.
— Chris Welch, ISA Certified Arborist