What Plants Will Die Near Black Walnut Trees?
- Roots of black walnut trees secrete toxins into soil.walnut image by ab from Fotolia.com
Black walnut trees (Juglans nigra) secrete a toxin called juglone that prevents competing plants from growing in the moist, fertile soil too close to the trees, a strategy called allelopathy. The juglone affects other plants if their roots touch or are within 1/4 to 1/2 inch of each other. Not all plant species succumb to juglone, however. While many common garden plants are known to die near black walnut trees, many other plants are not thoroughly researched or simply are documented as harmed by the trees. - In their natural habitat, black walnut trees' secretion of juglone into soil prevents other forest trees from growing nearby and shading or choking out black walnut seedlings. The University of Minnesota Extension Service's website lists broad groups of trees (by botanical genus) that die when they are too close to black walnut trees. Basswood (Tilia), birch (Betula), hackberry (Celtis) and pine (Pinus) are harmed by the juglone in the soil environment.
- Among the more widely known shrubs that do not grow well under black walnut trees are rhododendrons, azaleas, cotoneaster and cinquefoil (Potentilla). Other shrubs that falter or grow poorly near black walnuts are lilac (Syringa), yew (Taxus), hydrangeas and privet (Ligustrum). The shrubby vines of most cultivated grapes and blackberry brambles are susceptible to juglone.
- Observation of some common perennial flowers showed some were sickly when grown within 50 feet of a black walnut tree's trunk. These plants include columbines (Aquilegia), some Asiatic lily hybrids, some herbaceous peonies, false indigo (Baptisia) and fall crocus (Colchicum), according to a TreeBoss.net article that cites Purdue University plant lists. The perennial food crops rhubarb (Rheum) and asparagus grow poorly near black walnut trees, too.
- Flowers and vegetable plants belonging to the nightshade family, Solanaceae, are widely regarded as juglone-intolerant. Thus, flowerlike petunia and flowering tobacco are expected to fail near black walnut trees. Tomato, eggplant, potato and selections of sweet/green pepper also die when exposed to black walnut trees' juglone.
