Are Blueberries Compatible With Black Walnut Trees?

Types

• The Ohio State University Extension Service explicitly mentions the highbush blueberry (Vaccinium corybosum) as incompatible with the black walnut tree. Since blueberries are related to rhododendrons and azaleas, which also are incompatible with black walnuts, the gardener should assume all blueberries will not grow well planted near such trees. Of course, some hybrids or cultivars may perform better in proximity to the walnut tree, but overall the blueberry plant will not prosper and reach its fullest potential.

Safe Distance

• Avoid planting any blueberry shrub within 50 feet of the drip line of a black walnut tree. The drip line is the reach of the outermost branch tips of the tree's leafy canopy. Actively growing roots radiate outward well beyond the drip line. If you plant blueberries close to a young walnut tree, eventually the tree's roots may reach the roots of the blueberry shrubs as the tree matures. The walnut roots release juglone, killing the blueberry roots they come in contact with.

Juglone Insight

• While juglone is excreted by walnut roots, the chemical compound also exists in leaves and walnut fruits. Fallen debris from the walnut tree decomposes and releases juglone. Therefore, do not use any compost created from walnut tree leaves or husks as mulch or soil amendment in a bed filled with blueberries. Even after a walnut tree is cut down, the slowly dying roots that remain continue to excrete juglone.

Solutions

• If the only space available is within the root zone of a black walnut tree, a raised bed or large container may be a solution. As long as no walnut tree roots or leaf litter invade the raised planting bed filled with fertile soil, a blueberry will grow well. More frequent watering and fertilizer application are needed when growing blueberries in containers or in raised beds.