Facts About the Buckeye Tree
The California buckeye (Aesculus californica), also called horse chestnut, is a large deciduous shrub or small tree that grows wild in the western United States. According to the Lady Bird Johnson Wildflower Center Native Plant Database, it is the only type of buckeye native to the west. This member of the Hippocastanaceae family thrives on woody slopes and in arid canyons throughout coastal California and Sierra Nevada. Gardeners occasionally cultivate them as native ornamental plants because of their showy spring flowers.
The California buckeye tree grows approximately 10 to 20 feet tall with a 30-foot spread. Its low branches and multiple trunks are covered with silvery bark, and it has a naturally symmetrical, rounded form. This plant tends to form thickets in the wild. The leaves are palmately compound, or shaped like the palm of the hand, and composed of between 5 and 7 individual leaflets. New leaflets are pale green, but mature to a deep green. Each leaflet is oval shaped, with pointed tips and finely serrated margins. California buckeye trees in the wild usually lose their leaves by July, but the leaves will last until autumn if the plant receives a moderate amount of water.
Flowers and Fruit
An attractive floral display grace the California buckeye in the spring. Sunset describes it as looking like a "giant candelabra," as 4- to 8-inch-long elongated clusters of creamy white blossoms with extended orange stamens cover the shrub. Smooth, pear-shaped seed capsules, 2 to 3 inches long, replace the blossoms. As the season continues, the capsules split open to release glossy brown seeds.
California buckeye is hardy in U.S. Department of Agriculture plant hardiness zones 6 through 8. It thrives in nutrient-poor, dry soil with moderate to low amounts of water. This rapidly-growing tree, which propagates from seed, can grow as much as 10 inches per year. You can grow Aesculus californica by harvesting its seeds late in fall. The seeds dry out quickly, so plant them immediately in a spot that has well-drained soil and full sunlight. Water the young shrub regularly during its first year of growth. It will become established after the first year. Mature plants are low maintenance and require only occasional pruning.
California buckeye seeds are poisonous to both humans and animals. Squirrels and chipmunks are the only animals that can safely consume the raw seeds. The flowers are an attractive source of nectar for hummingbirds, but the nectar and pollen is highly toxic to bees, so avoid planting these shrubs near apiaries.