Planting under Black Walnut Trees

December 30th, 2011

What plants grow under black walnut trees? This is a question that we at Greenwood Nursery hear quite often. It is a good question, because not all plants thrive in close proximity to black walnut trees.

The black walnut secretes a chemical from its ...

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Juglans nigra, commonly known as black walnut, is the largest of the twenty species of Juglans native to the United States. It easily grows to a height of 100 feet; its strong, straight trunk and magnificent canopy enhance most any landscape that has an appropriate scale for the trees massive size.

It is prized by the high-end furniture market because of its uniformity, durability and the luxurious chocolate-brown color of its heartwood. Many landowners, who have a few acres to spare, are planting genetically superior black walnut trees as an investment which will mature in 25 to 30 years.

Horticulturists discovered that certain plants did not do well, while some withered and died, when planted close to or underneath the canopy of black walnut trees. Black walnut trees secrete a biochemical substance known as Juglone. These secretions sometimes drip from the leaves down onto plants and ground below and leaches out from the roots below ground as well. The process is known as allelopathy.

Though Juglone is a poison to many plant varieties, making it difficult in planting under black walnut trees. However, there is still a large number of shrubs and perennials that can be safely planted under the canopy or near black walnut trees that are resistant to the effects of Juglone.

Avoid planting the following near or under the canopy of black walnut trees: Apples, white birch, mountain laurels, blackberries, blueberries, tomato plants, azaleas, chrysanthemum, crocus, hydrangeas, lilacs and rhododendron.
And now for a few plants that can be planted near Black Walnut trees: most grasses, aster, shasta daisy, vinca, hostas, phlox, wisteria, Morning Glory, ajuga, solomon’s seal, and Virginia creeper.Tolerant trees and shrubs include arborvitae, white ash, american beech, catalpa, black cherry, flowering dogwood, forsythia, hibiscus, red maple, japanese maple, oaks, privet, eastern redbud, sumac, sycamore, tulip tree, euonymus, rosa rugosa, viburnum (except maresii), and heucheras.A word of caution: Many factors, other than the presence of Juglone, will affect the viability of your trees and plants. Soil, moisture, temperature, shade and sunlight all play a role so results in growth may vary.

Visit Greenwood’s page on Planting under Black Walnut trees for a selection of plant varieties that will grow under the canopy of the black walnut trees.

More info on plants that will and will not grow under or near black walnut trees:
Ohio State University Extension Black Walnut Tree Fact Sheet 
Purdue University 
West Virginia University Extension Service 

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