Will the shrub Mahonia bealei (leatherleaf mahonia) survive around the roots of a black walnut tree?
Answer
Kara, Black walnut trees have a substance called juglone that is toxic to many plants. Especially azaleas, rhododendrons, and similar ones. Mahonia is more than likely affected also. So it is better to not plant it there. Hostas seem to be ok. But a suggestion that often works if you really want plants under the black walnut is to put plants that meet the sun/shade requirements under the tree in various pots and make an interesting arrangement. Or use a larger planter. Mahonias are understory trees and like acidic (pH in low to mid 6's), moist, well-drained soils, especially for the first three years. They also prefer part sun, perferably morning, rather than scorching afternoon sun that might cause the leaves to "burn" or turn brown. Also a large detriment to their appearance is winds as the winds dry out the leaves. So, they should be planted in part sun, in acidic, moist, well-drained soil in a protected location away from black walnuts! They are beautiful plants and I'm sure you will enjoy them for years to come. ep