Treevia – Melting over butternuts

Butternut tree nuts develop in a lemon shaped, green husk and mature in late summer.

Have you ever nibbled on a nut from a butternut tree? If you did, you’d know why squirrels melt at the mere thought of them. Sadly, these tasty seeds are vanishing from our forests. Butternuts are threatened by butternut canker, a fungal disease which slowly kills infected trees. Stricken trees gradually lose their branches and develop black oozing cracks on the bark. There is no cure for the disease. The situation is so serious that butternut is listed as an endangered tree in Ontario and across Canada.

A butternut tree infected with butternut canker showing a blackened open sore.

Most butternut trees will be infected, but some can survive for years and produce seed. These surviving trees continue to be protected and their seeds can be used for tree planting efforts. If they continue to tolerate the canker they can be cloned to breed new generations of genetically tolerant trees. Cloning a butternut involves grafting them onto seedlings of black walnut, a native cousin, which to date is not affected by the canker. As if that wasn’t curious enough, there are hybrid trees of butternut and the exotic Japanese walnut. The Japanese walnuts and their hybrids are more resistant to the canker. Both have been widely planted and can produce seeds. However, it is not known how these hybrids would survive in a forest setting and whether they could replace butternut as a favoured wildlife food crop.

Our forests in general, not just butternuts, are under a great deal of stress. Introduced invasive pests and diseases are killing many native trees. The best defense a forest may have is the diversity of the tree species within it, which hopefully pests nor diseases can wipe out entirely. You can plant butternut trees on your own property and can keep an eye on them over the years to see how they fare. Watch for the long green male catkins that develop in May before the leaves flush, and the red tipped flowers which follow. The nuts develop in a lemon-shaped green husk and mature in late summer. But don’t confuse them with black walnuts, which grow in a round husk a little smaller than a tennis ball.

Butternut tree seedlings are occasionally available through our Tree Seedling Program. For all the details please see our website:

Butternut flowers & leaves - Brampton, Ont
Male catkins of a butternut.
Red female flowers of a butternut tree.

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