Aesculus x carnea

I’ve got a soft spot for flowering trees. I’ll slow down to a crawl on the road to catch a glimpse of a tree swathed in color. So when I stumbled onto a photo of A. x carnea, I added it to my landscape wish list.

Red horsechestnut is purportedly a cross between A. hippocastanum and A. pavia, but there’s some debate among horticulturists. No matter its origin, Aesculus is a genus worthy of consideration. It makes a good shade tree, has fabulous flowers and attractive, deep-green foliage, and attracts hummingbirds, butterflies and bees. It’s one of those trees I could spend hours observing in an overstuffed chair from the comfort of my screened-in porch. (I’ll add that to my “things to do when I retire” list.)

Pink to bright-red flowers appear each spring on panicles up to 8 inches long at each branch tip. Flowers are complemented by deep-green, coarse-textured foliage.

It takes on a pyramidal shape as a young tree and matures to a rounded habit.

It produces messy fruit in fall, so it’s not recommended as a street tree. Avoid sunscald on the trunk by leaving lower branches on small trees.

A. x carnea grows best in full sun or light shade and in moist, well-drained acid soils. It will grow in slightly alkaline soil. It grows 8-12 feet in 10 years.

One drawback of the cross is A. hippocastanum is susceptible to leaf scorch, said Tim Cramer, horticulturist at Heritage Seedlings in Salem, Ore. But the hybrid is somewhat less susceptible to scorch.

The pavia breeding gives the hybrid its burst of red and pink.

In production, A. x carnea works best as a balled-and-burlapped tree. The hybrid doesn’t have fine roots, so it’s not recommended for container production, Cramer said.

Starter plants need to be staked, but once they’re actively growing they have good apical dominance and support is not needed, he said.

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Some cultivars

‘Briotii’ is slightly smaller than the species with larger flower clusters and deep-red flowers. It’s the most popular cultivar of the species, said Mark Brand, professor at University of Connecticut’s Plant Sciences Department. It’s less susceptible to fungal disease than other Aesculus, Brand said.

‘ Fort McNair’ has pink flowers with yellow throats.

‘O’Neill Red’ is a round-headed and slightly smaller tree, which grows to 35 feet tall. Its bright-red flowers are more vibrant than ‘Briotii.’

Other considerations

Cramer’s choices for Aesculus hybrids are crosses with A. glabra such as A. x  arnoldiana for its fall color and hardiness to Zone 3.

The glabra types are resistant to scorch, and A. x arnoldiana withstands heat and humidity, Cramer said.

Leaves of A. x  arnoldiana ‘Autumn Splendor’ turn brilliant maroon-red in fall. Flowers are yellow with an orange-red blotch.

For more: Heritage Seedlings, (503) 585-9835; www.heritageseedlings.com. Mark Brand, University of Connecticut, (860) 486-2930; mark.brand@uconn.edu.

Photo courtesy of Michael Dirr.

Specifics

Name: Aesculus x carnea.

Common name: Red horsechestnut.

Description: Medium-sized deciduous tree with a bonus spring display of pink to red flowers on 5- to 8-inch panicles. Dark-green leaves persist until late October. Grows 50 feet high and has a rounded crown.

Hardiness: USDA Hardiness Zones 4-7, although some sources cite success in Zone 9.

Propagation: Seed, cuttings and grafting.

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Landscape uses: Shade tree, specimen tree or en masse for springtime drama.

- Kelli Rodda

June 2008