We are in Toronto, with a space that has areas of full sun, part sun/shade, and full shade. Our back yard has about 80% coverage by tree of heaven roots. I’ve accepted that I must just continue pulling root systems out when I can. Our neighbours to the west have a spectacular Black Walnut. We are just on the edge of its canopy. I am looking for a list of flowers/bushes/small trees which could grow in this environment. Alternatively, a list of plants which don’t have a hope would be helpful.
Both of these trees use what one author calls “chemical warfare” to control their turf –they produce allelopathic chemicals that ward off potential competitors. In addition, the tree of heaven (Ailanthus altissima) competes with other vegetation by its abundant and brutish root sprouts.
Ailanthus usually prevents other native plants from becoming established; even after the mature tree is removed, unless its root crowns are treated, the tree will re-sprout, usually at a much faster rate than native plants – these other plants simply can’t compete. The best thing to do is to re-think eradication: focus on keeping an area as large as possible in your yard completely clear of the tree and its roots and plant something native in that area. However, the chemicals the tree released into surrounding soil might remain, making it a challenge to grow anything. This process might involve calling in a tree removal service to clear out at least part of your yard of the trees. See our “Ailanthus altissima (tree of heaven) – how can I get rid of it?” for more suggestions on dealing with the unheavenly invader. There do not seem to be lists of plants that successfully compete with this tree.
As for the black walnut (Juglans nigra), see our “Juglone and black walnut: a Toronto Master Gardeners Guide” – this includes lists of plants that can’t tolerate juglone, as well as many that can live in relative harmony with the tree.
If you are interested in further reading on this subject, pleaes see the link below:
Ontario Trees. Ailanthus https://ontariotrees.com/main/species.php?id=2001