The red buckeye tree is hard to miss when it burst into bloom at mid-spring.
The brilliantly hued red horsechestnut flowers are arranged in large (to 12 in ) cone-shaped flower clusters.
Red horsechestnut is a medium sized tree with a wide spreading, low-domed crown maxing out at 30-50 ft (9-15 m) across, and a maximum height of 40-70 ft (12-21 m). The tree is usually much smaller, however. The branches are often a little twisted and droop at their tips. Red horsechestnut has opposite palmate leaves consisting of five (usually) or seven (occasionally) leaflets, each around 6 in (15 cm) long. The leaflets are usually wrinkled and slightly twisted. The flowers are dark red or rosy red with yellow centers, borne in upright cone shaped clusters (panicles) 8-12 in (20-30 cm) tall. The seeds are shiny buckeyes (usually two) encased in a spiny spherical husk about 1.5 in (4 cm) in diameter. Red horsechestnut, created by crossing two other Aesculus species, is a tetraploid, meaning it has four, instead of two, sets of each chromosome.
The cultivar A x carnea 'Briotii' has larger flower clusters consisting of flowers with blood red petals. 'O’Neil Red' has even brighter red flowers. 'Rosea' has rose-pink flowers.
The result of a backcross between red horsechestnut and one of its parents, common horsechestnut (A. hippocastanum), Aesculus x plantierensis is a sterile triploid and a larger tree whose flowers are pale pink and fruits remain undeveloped. It is sometimes referred to as the cultivar A. x carnea ‘plantierensis’.
Red horsechestnut (Aesculus x carnea) is a hybrid species resulting from a (presumed) chance cross between the shrubby red buckeye (Aesculus pavia) from SE North America, and common horsechestnut (A. hippocastanum), a much larger tree from Europe. Red horsechestnut was first introduced in the early 1800s in Germany, but little else is known of its origin. This is a very popular ornamental tree in Europe, especially the U.K., but not seen as much in the U.S. Aesculus x plantierensis, the backcross between A. x carnea and A. hippocastanum, had its origin at a nursery in France.
Position red horsechestnut in part sun to part shade. Full sun is OK in cooler climates. Moisture: The chestnuts like a moisture retentive, but well drained soil. During prolonged droughts, they benefit from supplemental watering. Red horsechestnut is, however, slightly more tolerant of drought than its parent, common horsechestnut (A. hippocastanum). Still, the root zone should be mulched where summers are hot and dry. Hardiness: USDA Zones 4 - 8. Propagation: Unlike most hybrid species, the seeds of red horsechestnut are fertile and come true to type. These may be sown as soon as the husks split open. The backcross Aesculus x plantierensis is sterile and must be grafted onto other Aesculus species.
Red Horsechestnut trees (this one is in bloom) grow slowly to an eventual height of more than 60 ft.
Red horsechestnut (Aesculus x carnea) is used as a lawn specimen and shade tree. It has a more eye-pleasing rounded shape than other Aesculus species which tend to be taller and more cylindrical-upright. The large showy flower clusters and tropical looking foliage are attractive in spring and summer. Fall color is excellent when the leaves turn yellow to orange. Smaller than many other members of the genus, and a slow grower, red horsechestnut is suitable for smaller landscapes such as residential lawns.
Older specimens sometimes develop "warts" on the trunks that eventually decay. Red horsechestnut, like others in the genus, produces a lot of litter from leaves and prickly fruits, and may not be desirable in some situations such as over sidewalks, border paths or patios.
The generic name, Aesculus, was coined by Linnaeus and means an oak with edible acorns. Fortunately, he apparently did not eat one of the buckeyes himself (see WARNING).
All parts of the horsechestnuts and buckeyes, genus Aesculus, are mildly toxic if ingested.