Aesculus californica aka California Buckeye

Aesculus californica is also called California buckeye. It is part of the Sapindaceae family. It grows in California's valleys and foothills, and in mountain woods. Its range takes in the Coast Range and Sierra Nevada. It also grows in the Tehachapi Mountains. It grows by streams and on dry canyon slopes. This large shrub or small tree sheds its leaves. Most garden plants grow 12–30 feet (3.7–9.1 m) tall. They can spread to 30 feet (9.1 m). RHS gives a taller range, up to 39 feet (12 m).

One or more trunks hold a broad crown. Its shape can be flat or round. The short trunk has branches that rise and spread out. Smooth, silver-gray bark adds interest when the tree is bare in winter. Young twigs are thick and reddish brown, then turn darker. Leaves grow in pairs along the stems. Each palmate leaf has parts that spread like fingers. These parts, called leaflets, number five, or sometimes seven. Their edges have fine teeth. Their tops are dark green and shine. Their lower sides are paler. The leaves may turn yellow in fall. New leaves can grow in late winter.

The sweet-scented blooms range from cream-white to pale pink. They grow in upright groups at the branch tips. Long stamens reach past the petals. Sources give bloom times from February–March to May–June. The blooms draw hummingbirds and butterflies. Their nectar harms honeybees. Oregon State says the pollen also poisons honeybees. The fruit has smooth, tough skin and a pear shape. Inside are large brown seeds that shine. Each seed has a pale patch. The fruit adds interest in summer and fall.

Grow this buckeye in sun or part shade. Give it soil that drains well. Deep, rich soil with steady moisture suits it in gardens. It grows in clay, loam, sand, and chalk. It accepts a range of soil pH. It can cope with drought but drops leaves in hot, dry weather. Strong wind can cause leaf loss or brown leaf edges. Summer watering can keep leaves on until fall. Sources give USDA zones 7–8 and UK hardiness H6. Its broad shape suits use as a specimen in a large garden. Deer tend to cause little harm.

Bagworms and Japanese beetles may attack this plant. Borers, scale, and leaf-mining moths may attack it too. It may get mildew, rust, or anthracnose. Canker and honey fungus are also possible diseases. All parts can poison people and pets who eat them. Poisoning can cause vomiting and weakness. It can also cause paralysis and death. PFAF records past use of seeds as food. This use required care to remove toxins first. That past use does not make untreated seeds safe. PFAF also records uses as medicine. It notes the use of seed extracts for washing.