Growing under a Black Walnut tree

Asked May 28, 2016, 11:40 AM EDT

Can I grow veggies in a raised bed by my neighbors Black Walnut tree? I tried a few years ago and all the veggie plants died. I have new soil and would like to try again. I have since learned some plants are more susceptible to juglone. If veggies grow in the new soil are they safe to eat? Is there a way to prepare the raised bed with old soil before adding the new soil? Should I till the old soil first? Add a barrier? Landscape cloth? Cardboard? What are your suggestions? Thank you!

Hennepin County Minnesota trees and shrubs black walnut tree black walnut

2 Responses

If the vegetables grow they will be safe to eat, after all we eat black walnuts.
Black walnut (Juglans nigra), and to a lesser extent butternut (Juglans cinerea) produce a toxic substance that can be harmful to nearby plants. The trees produce the toxin juglone, which inhibits respiration in susceptible plants, causing growth to be retarded, stunted, deformed or kill some plant species. The greatest concentration of juglone in the soil exists within the dripline of the trees. Vegetable gardens in this area will experience problems. Plants susceptible to juglone are occasionally damaged well beyond the dripline as the roots of walnuts may extend 2 to 3 times the crown radius (the distance from the trunk to the dripline). Cutting down and removing the tree is of limited help, unless all roots are removed from the soil. This gets to be a tedious and complex job so tree removal is not recommended. Any roots remaining in the soil can continue to give off the toxin juglone, until the roots deteriorate and decay (sometimes several years). As a last resort, susceptible plants can be grown in above ground containers. Using raised beds with a barrier (the heaver the plastic the better, cardboard will deteriorate and chemicals can pass through landscape fabric) to prevent walnut tree roots from entering is a possible solution. Care must then be taken to keep the beds free of black walnut leaf litter or nuts. If a garden is separated from a black walnut tree by a driveway or other physical barrier, then root extension growth into the garden area may be limited and juglone toxicity problems minimized. Vegetables susceptible to juglone include asparagus, cabbage, tomatoes, peas, potatoes, peppers, and eggplants. Vegetable plants observed to be tolerant to Juglone: Lima bean; snap bean; beet; carrot; corn; melon; onion; parsnip; squash. Fruits: black raspberry, cherry.

I forgot to mention - do not mix the soils since there is already juglone present, instead put down your barrier then add new soil (you may use soil from elsewhere in your yard), them mix in compost and plant.