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Horticulture Questions and Answers

What can I grow under a black walnut tree?

Black walnut, a common tree in Missouri, produces a valuable wood and delicious nuts. Unfortunately, the tree often causes problems for gardeners. The problem is that black walnut trees and it's close cousin, the butternut, produce a substance called "juglone". This substance ends up in the soil around the tree roots and inhibits growth of many kinds of plants including some vegetables, flowers, and landscape plants.

Some plants affected by juglone include the following:

Vegetables and Fruits: tomatoes, asparagus, okra, cucumbers, cabbage, peppers, eggplant, potato, apples, rhubarb

Flowers: peonies, columbine, some chrysanthemums, Baptisia australis, lilies (particularly the Asian hybrids), 'King Alfred' and 'Ice Follies' daffodil, some peonies, flowering tobacco

Trees and Shrubs: white birch, apples and crabapples, Norway spruce, eastern white pine, mugo pine, basswood, hydrangeas, mountain laurels, privet, rhododendrons and azaleas, lilac, yew

Some plants that are not affected include:

Vegetables and Fruits: corn, beans, carrot, squash, melons, peach, cherry, plum, pears
Flowers: astilbe, begonias, pot marigold, hosta, zinnia, rose of Sharon, pansy, ajuga, coral bells, ferns, summer phlox, lungwort, grasses and most spring-flowering bulbs

Trees and Shrubs: red cedar (Juniperus), redbud, Japanese maple, hemlock, catalpa, arborvitae

If you want to grow plants that are sensitive to juglone and are not able to locate the plants beyond the root system of the tree your only option is to remove the tree. Since black walnut wood is valuable you may be able to recoup part or all of the expense of having the tree removed if you can find someone who will buy the wood. This is not always easy to do, but checking with local arborists, woodworking shops or the Missouri Department of Conservation may provide a lead. Check the yellow pages under "Tree Service" or "Woodworking". Whenever you are having trees pruned or removed, be sure the arborist is insured. For more information on selecting an arborist listen to message #3344 "How to Select a Tree Service".