I have a horse chestnut tree in my backyard and nothing grows under it. I’ve tried dozens of types of shade-tolerant plants, just to have them all die.
I thought it was because of the lack of light, but when I was chatting with Tena on the CBC Hamilton garden online chat, she told me that a horse chestnut is allelopathic and that is what she thought was the problem. This makes sense because the plants seem to be doing well for weeks, and then over a few weeks just die.
Do you have any suggestions on what will survive under my tree or should I just look into landscaping that doesn’t include perennials?
Thanks you, so much, for your help!
In researching your tree, Aesculus hippocastanum, several sources mention the probable presence of allelopathic properties. An older research paper from University of Georgia states that root, leaves and stems are pathways for the tree’s moderate chemical poison. No source has named the chemical that this tree is secreting. The Royal Botanical Gardens has listed this as an invasive species https://www.rbg.ca/archive/cbcn/en/projects/invasives/i_tree2.htm
Although Horse Chestnuts appears to be moderately allelopathic, it doesn’t seem to be a huge concern for other gardeners. In addition, the chemical secreted does not seem to be juglone, the chemical associated with Black Walnut trees, so juglone tolerant plants may not be what you want to plant. To lessen allelopathic effects, pick up the fruit and leaves. The lack of light from your tree’s canopy may still be affecting your growing conditions and thus thinning the tree might help.
The following Toronto Master Gardeners’ Guide to Shade Perennials should help you in deciding what plants you could try :
Hoping this will give you some gardening ideas.