Black walnut trees are prized for their edible nuts as well as their hardwood lumber, but it is important to take precautions when gardening with black walnuts trees. Problems that arise from the dropping of the dense, staining nuts as well as issues regarding negative affects on nearby plants make the black walnut tree a plant that needs to be handled with extra care.
Plant Away from Gardens
Black walnut trees create a relationship with nearby plants known as allelopathy in which the trees create a substance that affects other plants, explains the West Virginia University Extension Service. Black walnut trees produce a substance called juglone as well as hydrojuglone that are present in the bud, nut hulls, roots and all parts of the nut of the walnut tree. Through the production of this chemical, nearby plants experience yellowing and wilting of leaves as well as death due to the toxicity of the black walnut tree. Juglone does not travel far through soil because it has low water solubility, but its activity causes a toxic area just below the tree's canopy as well as near its roots. In order to prevent toxic shock or death to neighboring plants, the simple precaution includes keeping your garden in a location away from black walnut trees or using a raised bed to separate roots from the main soil level.
Plant in Naturally Occuring Areas
Though black walnut trees are generally resistant to pests and disease, maintaining them according to their care requirements is essential in keeping a healthy plant. A precaution regarding consistent vigor of the black walnut tree is to plant trees in areas where they naturally grow, explains the University of Minnesota Extension. Severely cold temperatures can injure black walnut trees and lead to death, while those trees that do not die but are injured become highly susceptible to diseases like canker. Keep trees away from narrow valleys and low land areas in which frost is more prevalent. If you observe any damage to leaves, nuts or twigs, your tree may be infested with insect pests like walnut caterpillars or aphids; however, vigorous trees are usually only damaged cosmetically. Additionally, livestock poses a great threat to black walnut trees as their tendency toward rubbing against and feeding on trees as well as creating more compact soil can lead to severe tree injury, according to the University of Minnesota Extension.
Beware of Staining
Black walnut trees produce fruit that contains black nuts and the nuts contain an oil within the kernel. The husk contains a yellow dye that turns black as the fruit ripens and begins to rot. It is important to take location into consideration when planting black walnut trees because whether gathering and harvesting nuts or dealing with nuts that have fallen from the tree, the husks will stain anything they come in contact with including other plants, cement and skin, according to the Union County College Biology Department. The precaution regarding staining focuses on location; a black walnut tree near a street or a driveway may lead to stained cars. Also, due to the immense strength of the nut's shell, damage to property is a potential problem when nuts fall from the tree, as is possible injury to humans and pets.