What Is a Red Horse Chestnut?

Red horse chestnut is a deciduous tree, or one that sheds its leaves each year, with the scientific name Aesculus x carnea. It is a hybrid species, a cross between Aesculus pavia, commonly called red buckeye, and Aesculus hippocastanum, the common horse chestnut. A medium to large shade tree, it is particularly known for its striking red blossoms. The name "horse chestnut" refers to the fruit, which are smooth glossy nuts resembling true chestnuts. Horse chestnuts are poisonous to humans.

The average height of a mature red horse chestnut is between 30 and 50 feet (about 9 and 15 m) when fully mature. Younger trees are upright and pyramidal in shape while older trees may have a round canopy. Horse chestnut leaves are large and give the canopy a dense appearance. Many red horse chestnuts grow as multi-trunked trees if they are not pruned to a single trunk when young.

Horse chestnut flower buds are large and slightly sticky. They open into elongated clusters of tubular florets gathered around a common stem, or floral spike. The groups of blossoms are usually 5 to 8 inches (about 12.5 to 20.5 cm) long. During the spring flowering period even the largest trees are covered with the showy blossoms.

The glossy dark brown nuts are enclosed in yellowish-green capsules covered with small spines. These are not edible by humans but several animals, including squirrels, will eat the nuts. Red horse chestnut leaves resemble those of other horse chestnuts, having five to seven broadly oval leaflets arranged in a fan shape. The leaves are dark green and retain their color until frost, when they turn light brown or gray and quickly fall.

Red horse chestnut trees usually grow best in full sun to light shade. They prefer well-drained soil that remains fairly moist, but established trees can put down deep roots and have some drought tolerance. These trees typically do best in soil that is slightly acidic but will grow in mildly alkaline conditions. The species resists some diseases better than the common horse chestnut does and is sometimes suggested as a substitute for that tree where disease is a problem.

These trees are usually planted as decorative specimen trees for their flowers or as shade trees. They need a chilling period during the winter, so will not grow well where temperatures do not usually fall below freezing. A red horse chestnut can tolerate occasional temperatures as low as -30 degrees F (-34.44 degrees C.)