Question: I understand that black walnut trees have a compound that inhibits growth in certain plants. I intend to garden several yards away from one. What precautions should I take to ensure the safety of my veggies? Also, since the leaves and twigs cannot be composted, what procedure is necessary to prevent this material from contaminating the rest of my compostable leaves?
Answer: It’s the roots of the black walnut that can cause the most damage to your veggies. They excrete a toxic substance that can harm some plants, including tomatoes and alfalfa. The toxic zone from a mature black walnut tree can extend up to 80 feet around the base of the tree, so if possible, plant your garden at least that far away.
You can compost black walnut leaves, but it’s recommended that you do so separately from your main compost pile. And since there’s no easy way to separate them from other leaves in your yard, we recommend just burning all the debris from the area around a black walnut.