Shrubs Compatible With Black Walnut

Black walnut trees secrete juglone, which will kill many shrubs and other plants growing under or near them. Juglone is a biochemical substance that's toxic to many plants; it's secreted from the black walnut tree's roots and leaves. But many shrubs are resistant to juglone and will survive near---if not under---black walnut trees.

Common shrubs resistant to black walnut juglone include dogwoods, red and Japanese maples, arborvitae, eastern redbuds, white ash trees, catalpa and hydrangeas. Others, according to Ohio State University horticulture studies, that commonly thrive near or under black walnuts include the American beech, black cherry trees, sumac, crabapple, tulip trees, and sycamores. Some species will do well in the vicinity of black walnuts, but should not be planted directly underneath a black walnut.

The February daphne and weeping forsythia will do well near black walnuts, as will several species of euonymus. Rose of Sharon is resistant, and the tartarian honeysuckle, Virginia creeper, and black raspberries will also grow near black walnuts. While not truly a shrub, the "red cardinal" clematis is resistant to the black walnut juglone. Two varieties of rhododendron are known to survive black walnut toxicity---the pinxterbloom (rhododendron periclymenoides) and the Gibraltar and Balzac, both of which are hybrids. Most species of viburnum will survive, and the Koreanspice viburnum is especially tolerant. Resistant fruit trees include peaches, nectarines, cherries and plums.

Other plants that are juglone-tolerant are mayapples, junipers, ferns, black locust, and autumn olive. Pawpaws and persimmons are also resistant. These plants---and most others compatible with black walnuts---will survive better if all the leaves, branches, nuts, and twigs of the black walnut are meticulously cleaned up on the ground around the trees.

Soil moisture will influence the survival rate for some plants, especially pines. In moist soils, black walnut toxicity will kill white and red pine. In dryer soils, however, the black walnut has very little effect on small pines.

English walnuts are often grafted onto the rootstocks of black walnut. Extra-sensitive plants such as tomatoes, potatoes, azaleas, and apple trees will not survive near an English walnut tree if it was grown on black walnut rootstock. According to the Ohio State University Extension Service, the toxic zone from a mature black walnut is within a radius of 50 to 60 feet out from the trunk. The juglone-toxic area extends outward each year as a tree grows, and can range out as far as 80 feet.

If you cut down a black walnut, the toxicity in the soil lives on. As the roots decay, they continue to secrete juglone, and it will be toxic for years. Especially susceptible plants, according to the University of Minnesota, include hackberry, most rhododendrons, birch, basswood, and most pines.