Aesculus flava aka Sweet Buckeye

Yellow buckeye, Aesculus flava, is a deciduous tree in the soapberry family, Sapindaceae. It also goes by sweet buckeye or big buckeye, and older books list it as Aesculus octandra. The tree grows wild in the eastern United States. Its range runs from Pennsylvania south to northern Alabama and Georgia, and west along the Ohio valley to Illinois. It favours rich, moist ground on river bottoms, stream banks, mountain slopes and damp coves.

This is the largest buckeye native to the United States. In gardens it usually reaches 50 to 75 feet (15 to 23 m) tall, with a spread near 50 feet (15 m). Mountain trees can pass 90 feet (27 m), and rare giants top 100 feet (30 m). The crown is oval to spreading, and the trunk is often straight. Young bark is smooth, grey-brown and blotchy. With age it breaks into large flat scales and plates. Stout twigs carry big, pointed, orange-brown buds that are not sticky.

The leaves are opposite and palmately compound, with five (sometimes seven) toothed, elliptical leaflets. Each leaflet is roughly 4 to 7 inches long. They turn dark green in summer and often colour yellow to pale orange in autumn. In spring, upright panicles about 6 inches (15 cm) tall carry yellow to greenish-yellow flowers. Bloom falls from April to June, depending on region. The fruit is a smooth, leathery, tan capsule 2 to 3 inches across, holding one to three glossy brown seeds. Its smooth husk separates it from the spiny-husked horse chestnut and Ohio buckeye.

Yellow buckeye grows in full sun or part shade. It does best in deep, fertile, moist but well-drained soil that is slightly acidic. Dry, hot or windy sites cause leaf scorch, and poor clay suits it badly. It copes with brief flooding. Sources rate it hardy to USDA zones 4 to 8, with some reports reaching zone 3, and RHS H5 in Britain. A fleshy taproot makes established trees hard to move. Young plants grow slowly.

The tree needs space, so it suits parks, campuses, large lawns, streamsides and woodland gardens. Many growers rate it the finest of the large buckeyes. Falling twigs, fruit and leaves make litter, so avoid streets and spots near houses. Grass struggles in its dense shade. Bees, butterflies and other pollinators visit the flowers. The light, soft wood once went into wooden ware, pulp and artificial limbs. People also used crushed seeds as a soap substitute.

Leaf blotch is the main disease. Powdery mildew, leaf spot, anthracnose, canker, coral spot and honey fungus may also appear. Pests include buckeye lacebug, Japanese beetles, bagworms and borers. Horse chestnut scale and leaf-mining moth can also attack. Even so, this species suffers less than other buckeyes. All parts, especially the seeds, contain saponins and harm people and pets if eaten. Native Americans roasted and leached the seeds for days to make them edible. Leave such processing to experts.