Horse chestnuts are magnificent large trees with attractively divided foliage. This hand-shaped foliage often turns tones of yellow in autumn, though the autumn foliage is often not as attractive as it is in some other Aesculus species. In spring, horse chestnuts bloom with clusters of white flowers, often shaded pink. When pollinated, these flowers give way to large, shiny seeds held in prickly coverings. These seeds look something like large chestnuts, but are quite poisonous.
Common name: Horse chestnut
Botanical name: Aesculus hippocastanum
Zones: 3 to 8
Size: To 80 feet tall and 70 feet wide
From: Areas of Europe
Family: Hippocastanaceae(horsechestnut family)
Sun: Full sun
Soil: Moist, but well-drained soil rich with organic matter is best. The trees tolerate a range of soil types from sand to a bit of clay. Avoid heavily compacted soils and heavy clays.
Moisture: Water during times of drought to keep the trees looking healthy. The leaves turn brown if not given a bit of additional moisture during times of drought.
Mulch: A 2- to 3-inch-deep layer of mulch over the soil around the tree will help conserve moisture, reduce competition from weeds or turf grass, and protect the tree’s bark from damage from lawn mowers or string trimmers. Leave a 4-inch gap between the mulch and the tree’s trunk.
Pruning: Pruning is generally unnecessary. The best time for pruning, however, is early winter.
Fertiliser: In most soils, fertilising is unnecessary. Use a balanced fertiliser in spring if necessary.
Seed: Gather seeds once they fall from the ground. Remove the spiny shells and sow the seeds immediately.
Cuttings: Take hardwood cuttings in early winter.
Anthracnose: If the leaves look scorched and spotted, the cause may be anthracnose. The spots may be grey, tan, or dark brown; dry or slimy. To deter the disease, prune off any infected branches, dipping your pruning tool in a bleach or alcohol solution between cuts. Prune some of the inner branches to keep good airflow in the tree’s centre.
Canker: Forms dark water-soaked cankers on the bark and branches of the tree. The cankers can spread, becoming larger. To deter the disease, prune off any infected branches, dipping your pruning tool in a bleach or alcohol solution between cuts.
Japanese Beetles: These beetles are darkly coloured and chew holes in plant leaves. Handpick the beetles from the plants and drop the insects in a bucket of soapy water. You might also try spraying with a pesticide made from neem, a tropical tree. Apply a bacterium to your soil called Milky Spore. This bacterium attacks the grubs from the beetles, but can take a couple of years to control the beetles.
Leaf spot: This disease appears summer or autumn in the form of yellowish or darker-coloured spots, often made of concentric rings. To deter this disease, prune some of the inner branches to keep good airflow in the tree’s centre.
Powdery mildew: Powdery mildew appears in mid- to late summer and looks like affected leaves have a greyish powdery covering on them. The leaves then drop off. To deter the disease, prune the plant to keep good air flow and avoid wetting the foliage in afternoons and evenings.
Rust: Usually looks like leaf spotting that’s followed by small masses of rusty-coloured powder on the leaves. Infected leaves die by the end of the season. To deter it, avoid getting the foliage wet; make sure there’s good air circulation around plants.
Scale: Scale insects crawl up plant stems, find a permanent home, and sort of plant themselves on the plant. They appear as small, raised spots and are easy to overlook. To deter scales, try encouraging beneficial insects; apply insecticidal soap or horticultural oil.
The beautiful fruits, that look similar to polished wood, are often used in crafts. These fruits are poisonous—keep them away from children or pets.
Aesculus hippocastanum ‘Aureovariegata’: Slow-growing cultivar with golden leaves. Colours better with some afternoon shade.
Aesculus hippocastanum ‘Baumannii’: This selection is smaller than the species-only growing about 50 feet tall, has showier flowers, and is sterile, so it doesn’t produce fruits.