Walnut wilt is a malady that affects vegetable plants in areas where walnut trees dominate the landscape. It is caused by the release of juglone through the roots, leaves and nuts of walnut trees. Juglone acts as a respiratory inhibitor to plants and will cause juglone-sensitive plants to wilt and die. Fortunately, some vegetables can be grown in the proximity of a walnut with little risk of walnut wilt. A diverse garden filled with onions, squash and even pawpaws can be grown near walnut trees.
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Many root vegetables can be grown within the vicinity of a black walnut tree. Onions, beets (except sugar beets), parsnips, carrots and wild yam will thrive if provided with adequate sunlight and proper nutrition. Of the major root vegetables, only potatoes and sugar beets show a significant sensitivity to walnut wilt. Root vegetables need more underground area to grow; dig down about 1 foot and make sure there isn't a thick root or large root network in the area that your carrots need for growing deep in to the soil.
Beans are good staples for a garden near walnut trees. Many kinds of beans, including soy, lima, snap and pole, are resistant to walnut wilt. The close cousin of the bean, the pea, isn't so lucky--peas cannot tolerate juglone at all and will die very quickly if planted within the drip line of a walnut tree. Differing levels of juglone tolerance have been observed among various cultivars of a single species of tolerant plants (and can even vary by soil type and region). If you intend to plant beans under your walnut trees, it may be a good idea to ask your neighbors what varieties they've been growing successfully.
Squash and Melons
Squash and melons can grow near walnut trees. A walnut-adjacent garden will grow ample amounts of summer squash, zucchini, scallop squash, pumpkin, watermelon, muskmelon and many others in the same family. Squash and melons tend to take up a lot of space with their spreading habits, so placing them under a walnut tree makes sense and frees up areas of your yard for planting juglone-intolerant plants, such as tomatoes.
Though many gardens are for bedding vegetables only, often gardeners will also keep a small stand of grains. Corn and wheat do particular well near a walnut tree. Some evidence indicates that being planted within the walnut's root zone may increase the growth of all kinds of small grains and corn.
Few large gardens are complete without some kind of fruiting bush, vine or small tree. Fortunately, there are many that can tolerate having a walnut for a neighbor. Crabapples, black raspberry, cherries, nectarines, peaches, plums, pawpaw and persimmons can produce fruit and even thrive near a walnut tree.