Buckeyes (Aesculus spp.) are deciduous trees with hand-shaped leaves and "eyed" seeds once carried by children as good luck charms. They range in hardiness from U.S. Department of Agriculture plant hardiness zones 3 through 9. The approximately 20 species also vary in size from the 12-foot mature height of the bottlebrush buckeye (Aesculus parviflora, USDA zones 4 through 8) to the up-to-100-foot stature of the horse chestnut (Aesculus hippocastanum, USDA zones 3 through 8). The "nuts" of all buckeyes are poisonous, and the pollen of California buckeye (Aesculus californica, USDA zones 7 through 9) is toxic to honeybees.
The 2- to 10-inch palmate leaves of buckeye trees generally have five to seven "fingers." They change color early, sometimes falling from the trees by late summer. Accustomed to a dry summer in its native habitat, the California buckeye may shed its leaves for that entire season. These early defoliations are more likely to occur where the trees aren't getting enough water. The Ohio buckeye (Aesculus glabra, USDA zones 4 through 7) is sometimes known as the fetid buckeye for the unpleasant scent of its foliage, but that scent isn't obvious unless the leaves are crushed.
Buckeye blooms appear in showy 4- to 12-inch plumes at the tips of the branches in spring to early summer. Their colors range from the white of horse chestnut, bottlebrush and California buckeye blooms, to the yellow of Ohio buckeye, to the hummingbird-attracting scarlet of red buckeye (Aesculus pavia, USDA zones 5 through 9).
The flowers are followed by leathery and sometimes spiny seed capsules. The capsules burst open in mid-autumn to reveal one to three shiny brown seeds per capsule, each with a lighter white scar, which is considered to resemble a deer's eye. If you wish to try growing a buckeye from seeds, gather those "conkers" before they dry out. You can plant the seeds immediately outdoors, 1 to 2 inches deep, or refrigerate them for three to four months inside a zipper-type plastic bag of damp seed-starting mix. After that chilling, plant them 1 to 2 inches deep in tree pots full of seed-starting mix at 70 degrees Fahrenheit. They should germinate within one week.
Buckeyes prefer rich, well-drained and slightly acidic soil. As understory trees, they can tolerate full sun in climates with plenty of rainfall. In drier regions, they should be grown in partial shade to help preserve their soil's moisture and prevent scorching of their leaves. However, they still need at least three to four hours of sun per day for prolific flowering.