Fruits of the common chestnut (Castanea sativa). Photo: Exeter Trees
Question: When I lived in France, we always collected chestnuts in the fall. There were wild chestnut trees in every forest, but I haven’t seen them since I moved to Montréal. Can you grow chestnut trees in Canada? I miss those charming fall walks in the woods with the family, then coming home to grill the chestnuts!
Answer: There’s a huge difference in climate between France and Eastern Canada and the European species, often called sweet chestnut or Spanish chestnut (Castanea sativa), simply doesn’t do well there. It’s native to southern Europe, but although long since thoroughly naturalized almost everywhere in central Europe, it hasn’t proved well adapted to eastern North America and especially not the colder zones. Think of it as a tree for hardiness zones 6 or 7 to 8, which precludes all but the mildest Canadian conditions.
The same holds true for the different Asian species, such as Chinese chestnut (C. mollissima) and Japanese chestnut (C. crenata). They’re essentially also best in zones 6 to 8.
The only chestnut hardy enough for the Canadian climate is the American chestnut (Castanea dentata). It’s hardy in zones 4 to 8, but it is rarely grown, being highly sensitive to a devastating disease, chestnut blight (Cryphonectria parasitica).
So, let’s look into that…
History of an Ecological Disaster
Chestnut blight was accidentally introduced into North America on Japanese chestnuts planted around 1876 with the aim of establishing commercial chestnut orchards, because the Japanese chestnut, a tree half the height of the very tall American chestnut (up to 100 feet/30 m), was thought to be a better choice for orchard culture. Asian chestnut trees are quite resistant to chestnut blight and usually only suffer minor symptoms when they become infected.
At first, no problems were reported, but in 1904, a first American chestnut tree was discovered in serious decline in New York City. As it turns out, having never been in contact with the disease before, the American chestnut has no resistance to chestnut blight. After this initial infection, chestnut blight spores started quickly spreading, carried by the wind, killing more American chestnut trees, and advancing some 80 km annually, devastating forests in throughout the tree’s natural range.
In less than 50 years, the American chestnut, despite having been one of the commonest species in its natural range, essentially the Eastern United States and The Niagara peninsula of Ontario (it is estimated that a quarter of the trees in the region’s forests had been chestnut trees), was gone. It’s said that about 2 to 3 billion trees were killed.
The situation today is dire and the American chestnut is considered “critically endangered,” only a step away from “extinct in the wild.” Most people in its natural range have never seen an American chestnut. Curiously, the disease seems less virulent in the colder, moister part of the tree’s range: there are still some 600 to 800 chestnut trees in Michigan and perhaps 2,000 in Southern Ontario, but very few in the South.
Typically, a tree stricken with chestnut blight dies to the base, but often produces stump sprouts. These young trees grow quite vigorously for several years, but when they reach about 15 to 20 feet (6 to 9 m) in height, often just as they begin to flower, the cankers caused by chestnut blight develop and they die back again, usually before producing any nuts. Some ancient stumps still produce sprouts to this day, more than 100 years after the first infestation. These stump sprouts are the surviving chestnut trees of Michigan and Ontario. This inability to reproduce naturally has led some specialists to consider the American chestnut functionally extinct.
Hybridization to the Rescue?
There have been many attempts to restore the species by developing naturally resistant American chestnut trees and programs along that line continue to this day. A few trees have sown some natural resistance and seedlings from them are being raised and crossed with other resistant trees to try and produce pure American chestnut trees with natural resistance to chestnut blight. To date, the results have not been very promising.
Other programs see the solution in interspecfic hybridization with Asian chestnut trees. By crossing these naturally blight-resistant Asian trees with American chestnut trees and keeping any disease resistant trees that appear, then backcrossing with American chestnuts again to create trees that look just like American chestnuts, the hopes are that it will be possible to develop hybrid chestnut trees that are virtually identical to American chestnuts in appearance, adaptability and vigor, yet perfectly resistant to chestnut blight. Thus, these hybrids could eventually be used to reintroduce the species into the forests throughout the American chestnut’s natural range.
These programs have had some success and such hybrids are widely available. Among the problems is that chestnut blight seems to mostly attack mature trees. As a result, cultivars that appear to be disease-resistant and are promoted as such often turn out to be susceptible decades later. Many orchardists growing hybrid chestnuts are finding they get great growth and production at first, then have to replace the trees after 20 years or so when the mature trees are killed back by blight.
Also, so far hybrid chestnuts have also been proven to be less hardy than the native American Chestnut (zones 4 to 8). The hybrids usually only thrive in zones 6 to 8, although extra-hardy cultivars can be worth trying in protected spots of zone 5, making their culture possible in Montréal.
There is another option open to gardeners in areas where the American chestnut was never native and therefore where chestnut blight has never been known to occur.
Many people are discovering that it’s possible to grow the true American chestnut in such areas. For example, in the American West, especially in Oregon, some 2,000 miles (3,000 km) from any wild chestnut tree, there are American chestnut orchards that produce very well and no disease has occurred.
In your province, Quebec, just beyond the tree’s natural range, the disease does not seem to be present either. There are American chestnut trees in various Quebec botanical gardens and arboreta (the Montreal Botanical Garden and the Roger Van den Hende Botanical Garden, for example) that are doing perfectly well. So, you might be able to grow American chestnuts in your own garden or encourage your local municipality to plant some in a park.
One way of obtaining chestnut trees would be to harvest fallen chestnuts* in these gardens and sow them in your home garden. I did it myself and an American chestnut tree still grows in one of my former gardens.
*Do note that botanical gardens and arboreta are not likely to object to the harvesting for propagation purposes of a few chestnuts that have fallen to the ground. There is a kind of “gentleman’s agreement” in this regard between these gardens and home gardeners. Just be discreet. On the other hand, there have been cases of people showing up to harvest all the chestnuts for personal use or resale and such razzias will definitely not be tolerated.
You can also find American chestnut trees as well as hybrid chestnut trees at various nut nurseries. Nutcracker Nursery and Arboquebecium Nursery are two in Canada that offer both American chestnuts and hardier hybrid chestnuts while Grimo Nut Nursery and Hardy Fruit Tree Nursery sell hybrids only.
American readers will find many nut nurseries carrying American chestnuts and especially hybrid chestnuts, including The Nursery at TyTy and Burnt Ridge Nursery. International readers would do best to avoid the American chestnut and use locally offered varieties better adapted to your climate.
And when planning the planting of chestnut trees for your own pleasure, remember that you always need at least 2 different clones to ensure good pollination and fruiting. It normally takes at least 3 to 5 years before the first chestnuts ripen while trees reach maturity and peak production around the age of 15 to 25 years, depending on the cultivar and the climate. Usually, a mature chestnut tree produces up to 50 to 100 lb (25 to 50 kg) of chestnuts per year.
Chestnut or Horse Chestnut?
I’m sure many readers are thinking confidently “We have a chestnut tree in our yard,” and maybe you do, but that’s unlikely. That’s because most “chestnuts” grown in North America (and even in Europe) are horse chestnuts, an entirely different tree. Chestnuts, discussed above, belong to the genus Castanea and are edible. They’re in the beech family (Fagaceae). Horse chestnuts, from the genus Aesculus, are poisonous and are in the soapberry family (Sapindaceae). Other than nuts of similar appearance, the two trees are very different and are in no way related. You will find a key showing how to distinguish the two in the article Chestnut or Horse Chestnut?.