Plants That Will Grow Under Black Walnut Trees

Are you seeking plants that will grow under the Black Walnut trees on your property?

Black walnut trees can be a tricky plant for gardeners, as this species of plant produces a toxic substance called juglone via its root system. Other trees that emit this toxic substance include butternut and Persian walnut trees that are grafted with black walnut. (Notably, persian walnut seedlings that are grafted onto persian walnut rootstocks do not produce deadly toxins that kill other plants.)

The juglone leaches out into the surrounding soil and it can kill nearby plants within a period of just 30 to 60 days. Some of the most susceptible plants include: Tomato plants; Blackberry bushes; Azalea; Mountain laurel; Apple trees; Blueberry bushes; Potato plants; Rhododendron bushes.

The toxic zone can extend up to 80 feet from the trunk of a large mature black walnut tree, though the typical no-grow zone usually extends 50 to 60 feet. This tree's tendency to kill off nearby plants is enough to leave many gardeners scratching their heads, wondering "what can I plant that will grow under a black walnut tree?"

Not to fear! Not all plants are sensitive to the juglone that's produced by the black walnut tree. There are a number of trees, annuals, perennials, shrubs, vines and ground-cover plants that are resistant to juglone.

Some of the most popular plants that are often planted near a black walnut tree include:

Arborvitae

Bugleweed

Christmas Fern

Cinnamon Fern

Daylily

Crested Wood Fern

Eastern Redbud

Elizabeth Sedum

Creeping Phlox

Creeping Stonecrop

Grasses

Heuchera

Honeysuckle

Hosta

Japanese Maple

Viburnum

Lamb's Ear

Tartan Honeysuckle

Virginia Creeper

Forsythia

Wisteria

It appears that the black walnut tree actually enhances and promotes growth in a limited number of plant species, especially grasses such as Kentucky bluegrass.

Despite the fact that the black walnut tree's toxins can kill many nearby plants, they are still favoured by many for their beautiful appearance and their ability to prevent soil erosion and offer shade, particularly on pastures. They are especially popular in pastures.

It's important to note, though, that juglone is present in the black walnut tree's wood, bark and leaves. The wood chips can cause problems in some animals, particularly horses.

Composting black walnut leaves will result in the degradation of the juglone toxin, which breaks down in 2 to 4 weeks when the leaves are composted alone, or up to 2 months if they're mixed with soil and other compost matter. So it's generally safe to use fully-composted leaves on juglone-sensitive plants.

What to Plant Under Black Walnut Trees

What are plants to plant 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 begin planted near or under black walnut trees.

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:
Purdue University 

For more information on growing black walnut trees as an investment, visit Greenwood Nursery GSP Black Walnut Trees.

Common Black Walnut Trees