Hello! I have extensive gardens around my house, which I bought 3 years ago. I removed all the grass on the property, and instead landscaped with perennials, shrubs and small trees. The neighbour behind my house has a small shed which is a couple of feet away from the chain-link fence separating our properties, and in the corner beside their shed and right next to the fence — where they cannot see it — is what I believe is a young walnut tree, growing vigorously, which I noticed when I started to clear out an old compost pile beside the fence in this area. I know its roots’ juglans will cause problems eventually with most of my plantings (and perhaps the mature lilac shrubs along the fence line), but I wondered how much time I have before it really becomes a problem, and if I need to sneak through the opening in the fence sooner rather than later and dispose of this tree, and what would be the best way to do it. Thanks for your advice!
You certainly will have a problem if what you suspect is a black walnut tree (Juglans nigra) growing in the corner of your neighbours garden. Speed is of the essence here if you want this walnut tree removed. The more established it becomes the harder it will be to do this. Furthermore, in Toronto we have the Private Tree By-Law that regulates the injury or removal of privately owned trees which measure 30cm or more in diameter when measured at a height of 1.4meters above ground level. Hopefully this tree hasn’t reached this size.
Walnut trees produce a chemical called juglone, which inhibits the growth of many other plants by depriving them of the energy to grow well. Eventually such a tree will affect what you have planted in your garden. You mention that your neighbour many not even know that the tree is in their garden. What you really need to do is have a conversation with your neighbour. Explain the problem to them, even provide them with an information sheet (see below) and hopefully they will agree to have the young tree removed.
If you would like to confirm the identification of the tree you can send in a picture showing the tree shape and leaves to Ask a Toronto Master Gardener.
Please find links below to the Toronto Master Gardener Factsheet on Juglone and Black Walnut and the Ontario Ministry of Agriculture, Food and Rural Affairs (OMFRA) guide to Walnut Toxicity.
https://www.omafra.gov.on.ca/english/crops/facts/info_walnut_toxicity.htm