What kinds of plants should I grow beneath black walnut trees? We at Greenwood Nursery get this question pretty frequently. It’s a valid question, as not all plants do well when they are first planted close to or underneath black walnut trees. The largest of the twenty Juglans species that are endemic to the United States is Juglans nigra, also referred to as black walnut. It can easily reach a height of 100 feet, and its spectacular canopy and strong, straight trunk brighten almost any landscape with an adequate scale.
Due to its regularity, sturdiness, and opulent chocolate-brown heartwood color, it is highly prized by the high-end furniture industry. Many landowners who have a few extra acres are investing in the growth of genetically better black walnut trees, which will reach maturity in 25 to 30 years.
When planted near or underneath the canopy of black walnut trees, horticulturists found that certain plants did not thrive while others faded and died. Juglone is a biological compound secreted by black walnut trees. These fluids can leak out of the roots underground as well as occasionally flow from the leaves down onto the plants and the ground below. Allelopathy is the term for the process.
Although many plant species are poisoned by juglone, this makes planting beneath black walnut trees challenging. There are still a lot of shrubs and perennials that can be planted without risk next to or under black walnut trees since they are juglone-resistant.
Apples, white birch, mountain laurels, blackberries, blueberries, tomato plants, azaleas, chrysanthemum, crocus, hydrangeas, lilacs, and rhododendron should not be planted next to or underneath the canopy of black walnut trees.
The majority of grasses, asters, shasta daisies, vinca, hostas, phlox, wisteria, morning glory, ajuga, solomon’s seal, and Virginia creeper are a few plants that can be grown next to black walnut trees.
Arborvitae, white ash, american beech, catalpa, black cherry, flowering dogwood, hibiscus, red maple, japanese maple, oaks, privet, eastern redbud, sumac, sycamore, tulip tree, rosa rugosa, viburnum (excluding maresii), and heucheras are among the plants and shrubs that tolerate it.
The survival of your trees and plants will be impacted by a number of factors in addition to the presence of Juglone, so proceed with caution. There are many factors that affect growth, including soil, moisture, temperature, shadow, and sunlight.
For a list of plant species that will grow beneath the shade of black walnut trees, go to Greenwood’s article on planting under these trees.
Juglone tolerance levels for hydrangeas
In many American landscapes and parks, black walnut trees may be found. They make a great choice for a shade tree. Black walnut trees come with a curse called juglone, despite having some advantageous qualities including shade, fruit for wildlife, and the potential for wood harvesting income.
Black walnuts naturally release juglone as a poison to drive out rival plants. Asparagus, rhubarb, peppers, tomatoes, eggplant, potatoes, hydrangea, peonies, lilacs, blueberries, azaleas, and true lilies shouldn’t be planted near a black walnut tree.
We’ll go over the plants you can and cannot grow beneath black walnuts, regardless of whether you’re planning to plant one or already have one of these monstrosities growing. Let’s start now!
What bushes will flourish beneath a walnut tree?
Juglone-Tolerant Shrubs
- Barberry (Berberis spp)
- Hazelnut (Corylus americana)
- Daphne (Daphne spp)
- Forsythia (Forsythia spp)
- Witchhazel (Hamamellis spp)
- The Sharon Rose (Hibiscus syriacus)
- Winter Hydrangea (Hydrangea arborescens)
- John’s wort (Hypericum prolificum)
What plants will blossom beneath a walnut tree?
There are numerous strategies for avoiding toxicity. One method—possibly the simplest method—is to exclusively plant plants that are compatible with black walnut trees when gardening around one. Any known plant that grows beneath black walnut trees without toxicological damage is considered a black walnut tree friendly plant.
Sugar maple, blooming dogwood, and boxelder are just a few examples of flora that can tolerate black walnuts. You can also grow begonias, hyacinths, and crocuses. These are all recognized as black walnut-tolerant plants. There are a lot more, and your neighborhood garden center may let you know about any unpalatable plants so you don’t have any issues.
What vegetation won’t flourish beneath a walnut tree?
When creating vegetable gardens close to black walnut trees, pick juglone-tolerant plants and place them in raised beds with barriers to stop the roots of the tree from penetrating the bed.
The growing season for vegetables is about to begin. The vicinity of black walnut trees is one factor to take into account when deciding where to place a new vegetable garden (Juglans nigra). I’ve discovered over the years as a gardener with many black walnut trees in my yard that there are a lot of plants that don’t get along well with black walnut. Always winning is black walnut. It reduces competition for resources by releasing juglone, a toxin from its roots that is toxic to many other plants and kills them. Juglone is also absorbed into the soil when precipitation comes into contact with rotting fruit, branches, and fallen walnut leaves. The highest concentration of juglone is found in plants growing underneath walnut tree canopies, although the roots of these trees spread well beyond their dripline and may also harm plants at a distance roughly equal to their height.
Juglone has a very low dosage toxicity potential. Removing the problematic walnut tree won’t actually solve the issue because plants that are sensitive to the toxicity of walnuts might still be harmed by the rotting roots of a walnut that was cut down many years earlier just by growing close to a leftover portion of walnut root. Nearly all of the root fragments will remain in the soil, and as they decompose they may continue to release toxins for years. Wilting, yellowing of the leaf, and eventual death are signs that a plant has succumbed to black walnut toxicity. Juglone slows plant respiration, which makes it difficult for species that are vulnerable to it to absorb water and nutrients, according to studies done to identify its effects.
What can a gardener who is determined to plant a vegetable patch near walnut trees do?
The Michigan State University Extension advises using juglone-tolerant plants when creating a garden around a walnut tree. Thankfully, a variety of plants, including lima and snap beans, beets, corn, onions, garlic, leeks, parsnip, carrots, cauliflower, soybeans, parsley, Jerusalem artichoke, melons, and squash, tolerate juglone. Avoid growing juglone-sensitive vegetables like tomatoes, asparagus, cabbage, eggplant, peas, peppers, potatoes, rhubarb, and cabbage.
Raised beds with bottom barriers made of wood, stone, or concrete prevent walnut roots from growing into the bed, but remember to keep the beds clean of walnut detritus such leaves, hulls, and seedlings. Mulch made of walnut wood or bark should not be used around delicate species.
What perennial plants can be found close to black walnut trees?
Will flowering plants such as dogwood, butterfly bush, or lilac grow underneath a black walnut tree. The intended planting bed is only 12 feet away from the tree limbs.
As you are aware, juglone is present in black walnut roots, leaves, and bark. Many plants are poisoned by this chemical. Research on plants that can withstand the chemical juglone is scarce. The garden should be kept at least 50 feet away from the tree and ideally 80 feet away for the greatest results. The floral plants and shrubs on the following list have been seen to flourish beneath black walnut trees. Weeping forsythia, Koreanspice viburnum, various kinds of viburnum, redbud (choose the Columbus or Minnesota strain for improved hardiness), and Rose of Sharon. The following perennials can also flourish next to a black walnut. tulips, sundrops (Oenethera), trillium, lamb’s ear, Dutchman’s breeches, cranesbill geranium, hosta, daylilies, and sundrops (Astilbe). See the Black Walnut Toxicity bulletin from Purdue University for a more comprehensive list.
Do hostas tolerate the shade of black walnut trees?
There are an astonishing number of varietal variations in hostas. Numerous variegated varieties are also available, with foliage colors ranging from light cream to blue. Hostas are fairly hardy plants that can thrive in both sunlight and shade, however new plantings in direct sunlight will require regular watering. Flowers come in a variety of sizes and beautiful hues, including white, pink, and lavender.
Because they are resilient, drought-tolerant, and appear to be immune to juglone, hostas are the most dependable perennials for growing beneath a black walnut tree. The hardiness zones for hostas are 4 through 9.
How is juglone neutralized?
Q. Due to the toxicity that the enormous black walnut trees emit, we have had difficulty getting anything to grow nearby. Is there any other option besides chopping them down to get rid of it?
A chain saw won’t help since the poison, known as juglone, is difficult to neutralize and can linger in the soil for years. Juglone is found throughout the entire tree, but it is most potent in the roots, which protrude well below the canopy.
Fortunately, juglone tends to remain in one place and is not a lethal substance to all. This gives you two options for coping: choose juglone-tolerant plants for the region inside the death zone, and keep delicate plants outside of it.
Measure the distance from the trunk to the drip line, multiply it by two, and then add an additional 10 to 30 feet, depending on the size of the tree, to find the juglone zone.
Within this fabled circle, nothing will grow, including tomatoes, peppers, eggplants, columbines, peonies, and chrysanthemums. Neither will lilies, hydrangeas, azaleas, rhododendrons, or azaleas. Leave out birches, apples, and pines.
What remains? When planted close to black walnut trees, Kentucky bluegrass and black raspberries appear to flourish. You can attempt squash, melons, beans, beets, and carrots if there is adequate sun.
The majority of spring bulbs and woodland plants like jack-in-the-pulpit, sweet woodruff, and cranesbill are examples of potential blooms. The best bets include hostas, asters, day lilies, coral bells, and Siberian iris. Most of the time, Euonymus, Japanese maples, viburnums, and hemlocks fare well.
Q. The directions said to space the 100 onion plants I purchased six inches apart, but if I do that, there won’t be enough room for them all. Can I plant them closer together and harvest any extras to use as scallions in my food?
A. Although you could, you shouldn’t for two reasons. The first is that onions grow roots upward rather than downward. When seedlings are planted close together, their roots eventually entwine, making it difficult to remove the green ones without damaging the primary crop.
Even more crucially, spring growth is crucial if onions are to develop into huge, firm bulbs by the time they are ready to be harvested. Whether it comes from short-lived siblings or weeds, competition slows them down.
Create a separate, little bed for the extras for optimal outcomes. Since you will be removing and eating them before crowding becomes a concern, they can be planted as close together as an inch apart as long as the soil is rich.
Q. There are numerous trees in the planned community where I reside that are, in my opinion, 11 or 12 years old. They are developing well. To “trim them out,” a tree service was hired last fall. It removed healthy branches of a good size. Is that a wise plan?
A. Although it is unsettling to watch healthy branches fall, pruning is often necessary.
You might trim the tree to encourage a more beautiful shape or remove low branches to widen the area underneath it. It might be wise to remove crossing branches or limbs with shaky angles of attachment for the sake of the tree. Additionally, you might thin to let in more light or to lessen the strain brought on by an accident, such as construction that harmed the tree’s roots.
Without more information, it is impossible to evaluate the wisdom of this pruning. And since the deed has already been completed, your reservations about it are, at least temporarily, unimportant.
When the trees have finished leafing out, they should look good. If they don’t, you should speak with the landscaping manager of your neighborhood.