This past week I was talking with a woman about lawn care. As initial conversations with our customers often do, we started chatting about gardens. She asked if it is possible to have a garden near a black walnut tree. The answer: yes and no.
Before moving to Zeeland we lived in Dearborn, Michigan on an urban lot (40 feet x 100 feet). Most of our backyard was garden and our neighbor directly behind us had a massive black walnut tree. I eventually learned that black walnut trees contain juglone and can be difficult, but not impossible to garden near.
The Morton Arboretum explains juglone this way: “Black walnuts produce a chemical called juglone, which occurs naturally in all parts of the tree, especially in the buds, nut hulls, and roots. The leaves and stems contain smaller quantities of juglone, which is leached into the soil after they fall. The highest concentration of juglone occurs in the soil directly under the tree’s canopy, but highly sensitive plants may exhibit toxicity symptoms beyond the canopy drip line. Because decaying roots can release juglone, toxicity may occur for several years after a tree has been removed.”
Ideally you would plan your garden as far away from a black walnut tree as possible. If your space simply doesn’t allow for that then use raised beds to combat some of the toxicity. Also ensure that your soil is full of nutrients so plants that do encounter the juglone have the best chance at health. Finally, avoid planting vegetables that are sensitive to juglone such as tomatoes, eggplant, asparagus, cabbage, and peppers. Instead plant vegetables known to tolerate juglone better such as beans, beets, carrots, melons, corn, leeks, onions, and squash. Now I know what you are thinking: what’s a backyard garden without tomatoes? For the health of your tomatoes consider a large pot and plant a variety of tomato suitable to container gardening.