A nut tree for Alberta?

“Chestnuts roasting on an open fire…” Christmas movies often show scenes of these smooth nuts on a grill over coals during outdoor activities. These nuts are “sweet chestnuts”. In North America, historically, the tree with this fruit was Castanea dentata, the American chestnut.

At one time, these trees were common in the forests of the eastern seaboard states of the USA and could be found in southern Ontario. Unfortunately, starting in the 1900s a fungal blight began killing off this native tree and, while there are still some stands, they are now considered functionally extinct or, at best, a species at risk. However, efforts are underway to restore the trees and introduce controls for the blight.

If we get to enjoy roasted chestnuts, the nuts are usually imported from Europe and are the fruit of the European chestnut, Castanea stativa. While the European tree is susceptible to the blight, the weather conditions where it grows seem to control the pest. To try keep this crop in North America, the European trees were introduced, but they are not as hardy as the native tree. They also no longer had the environmental control for the blight and could become infected.

So, what can a Calgarian grow if they want a tree that produces nuts? The options are limited, but one tree that has been rising in popularity is the Ohio buckeye, Aesculus glabra. It is the cousin of the common horse chestnut, Aesculus hippocastanum.

The Ohio buckeye, like the name suggests, is a North American native plant and is hardier than the horse chestnut. It is considered a small tree and has a slow to moderate growth rate. At maturity, it will typically reach 15 m in height. The crown is densely leaved, rounded, and has a spread of 9 m. The tree produces a tap root in its first year after planting, making it difficult to move, so be sure you plant it where you want it. It can live 80 to 100 years, so keep that lifespan in mind too.

What makes this tree stand out is its leaves, flowers, and fruit. The leaves are palmate. They are compound and look a bit like a hand with thick, lens-shaped, pointed fingers. In the fall, they turn a beautiful orange colour. In the spring the tree produces stunning spires of upward reaching light greenish yellow to cream-coloured flowers.

Another common name for the tree is stinking buckeye, as the flowers, and the leaves when crushed, are said to have a pungent odour. I have never noticed a smell when I’ve viewed these trees, but other people may be more sensitive to it. This tree in bloom is unlike any other tree that grows around here. The way the flowers’ spikes sit at the ends of the branches makes me think of candles decorating a Christmas tree. Once the flowers have faded, nuts develop.

The hard-shelled seed forms inside a green, thick, protective skin. The skin is covered in tightly spaced stubby spikes. As the seed matures, it turns dark brown with a light spot. This “buck eye” colouring is the source of the common name. It can take eight growing seasons before the tree is mature enough to flower and produce fruit.

Unlike the American chestnut, the Ohio buckeye leaves, bark, and fruit are toxic to humans and most animals when ingested. Squirrels, however, can eat the seed. The flowers are very popular with pollinators, including hummingbirds. 

If you would like to view some of these trees, Reader Rock Garden has a mature heritage specimen growing across the lane from the site’s dedication plaque. There are some younger trees along the south side of Memorial Drive, just west of Poppy Plaza. If you are looking to plant a tree this coming gardening season, add Ohio buckeye to your consideration list.

To learn more about gardening in the Calgary area, visit our website calhort.org.