Culture
Best grown in medium moisture, well-drained soils in full sun to part shade. Avoid dry soils. Responds to high heat or drought stress by dropping leaves. Leaves will remain on the tree longer, perhaps to early fall, if soils are given even and consistent moisture in summer. This shrub/tree has an early leaf drop and is deciduous for a good part of the year. Winter hardy to USDA Zones 7-8. May tolerate Zone 6b(-5°F) if given adequate protection. It prefers a Mediterranean-type climate with wet winters and dry summers and is infrequently grown in the eastern U.S.
Noteworthy Characteristics
Aesculus californica, commonly called California buckeye, is a large, deciduous shrub or small tree that is native to the foothills and valleys of the coastal ranges, Tehachapi, and Sierra Nevada Mountains of California in the western United States at elevations below 4,200’ where it is typically found on dry slopes, canyons and along waterways. It frequently grows in the wild as a spreading shrub to 15’ tall, but will sometimes grow as a small tree to 30’ tall. It is particularly noted for its (a) open flat-topped crown, short trunk, and spreading branchlets that are reddish to gray-brown when young, (b) smooth silver-gray bark, (c) opposite, lustrous, palmate, shiny dark green leaves, with each leaf having 4-7 but usually 5 narrow-elliptic leaflets (each to 6” long) with fine marginal teeth, (d) flower panicles (inflorescences to 4-12” long) which contain numerous, fragrant, creamy white to pink 4 to 5-petaled flowers with spidery anthers borne in May-June, (e) pear-shaped to fig-shaped, spineless, rough-textured, thick-husked fruit capsules (to 3” long) which split open in fall at maturity to reveal 1-2 dark brown nuts (each to 1” diameter) commonly known as buckeyes, and (f) sticky winter buds.
In California, this shrub/tree typically begins new growth in February but usually enters dormancy during the dry summer months. In the foothills of the Sierra, leaves dry up and are shed in late spring to early summer, typically turning brown and hanging from the tree throughout much of the summer. In the coastal ranges, leaves typically remain green much later in summer before dropping to the ground as long as soil moisture remains at acceptable levels.
Genus name is the Latin name for a kind of oak bearing edible acorns but applied by Linnaeus to this genus.
Specific epithet is in reference California being the native habitat.
Problems
For plants in the genus Aesculus, potential disease problems include powdery mildew, rust and anthracnose and potential insect problems include bagworms, Japanese beetle and borers. Leaf scorch (edges brown up) may occur in droughty conditions or on sites exposed to strong wind.
Early leaf drop typically occurs in areas with dry soils. All parts of California buckeye are poisonous to humans if ingested.
Uses
Single to multi-trunked small tree or large shrub. Very limited distribution in the United States in large part because of extremely early leaf drop. Landscape specimen.