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Black Walnut Tree Toxicity - What Plants Are Immune?

Walnut trees are fruitful and beautiful. I love to sit in the shade of one of my walnut trees and look out over the sloping garden. In our video Tricia shows you how to care for and prune walnut trees. walnut orchard Walnut trees definitely like their own space, and can be bad neighbors to certain plants. Find out the best companion plants for walnuts.

Black walnut tree toxicity

Black walnut trees load their roots, buds, and nut hulls with the juglone toxin (leaves and stems have smaller amounts of juglone). The toxin seeps into the soil and susceptible companion plants will turn yellow, wilt, and sometimes die. But wait, you say, I don't have a black walnut tree. Actually, most walnut trees are grown on black walnut rootstock these days, therefore the root system is likely to be rich in juglone. The soil under the canopy of the tree will have the highest concentration of juglone due to the combined effects of the roots, along with fallen leaves, hulls, and shells that are lying on the ground. Picking up this litter is good "orchard sanitation" for many Integrated Pest Management reasons, including decreasing the amount of juglone.

Companion plants for black walnut trees

  • Purdue University has informal lists of plants that tolerate juglone and those that are sensitive to it. Choose from the following list for best results in planting near black walnut trees or walnut trees grown on black walnut rootstock. Follow these guidelines for planting within the dripline of the tree and, according to the University of Wisconsin, up to 50'-80' from the trunk. Naturally you need to consider the sun and shade requirements of the plants, as well. Another source for tolerant and sensitive plants is K-State Master Gardener
  • Vegetables: lima bean; snap bean; beet; carrot; corn; melon; onion; parsnip; squash.
  • Fruits: black raspberry, cherry.
  • Landscape plants: arborvitae; autumn olive; red cedar; catalpa; clematis; crabapple; daphne; elm; euonymous (burning bush); forsythia; hawthorn; hemlock; hickory; honeysuckle; junipers; black locust; Japanese maple; maple (most); oak; pachysandra; pawpaw; persimmon; redbud; rose of sharon; wild rose; sycamore; viburnum (most); Virginia creeper.
  • Flowers and herbaceous plants: astilbe; bee balm; begonia; bellflower; bergamot; bloodroot; Kentucky bluegrass; Spanish bluebell; Virginia bluebell; bugleweed; chrysanthemum (some); coral bells; cranesbill geranium; crocus; Shasta daisy; daylily; Dutchman’s breeches; ferns; wild ginger; glory-of-the-snow; muscari (grape hyacinth); grasses (most); orange hawkweed; herb Robert; hollyhock; hosta (many); hyacinth; Siberian iris; Jack-in-the­ pulpit; Jacob’s ladder; Jerusalem artichoke; lamb’s ear; leopard’s bane; lungwort; mayapple; merrybells; morning glory; narcissus (some); pansy; peony (some); phlox; poison ivy; pot marigold; polyanthus primrose; snowdrop; Solomon’s seal; spiderwort; spring beauty; Siberian squill; stonecrop; sundrop; sweet Cicely; sweet woodruff; trillium; tulip; violet; Virginia waterleaf; winter aconite; zinnia.

Plants that are sensitive to black walnut tree toxicity

  • Vegetables: asparagus, cabbage, eggplant, pepper, potato, rhubarb, tomato.
  • Fruits: apple, blackberry, blueberry, pear.
  • Landscape plants: black alder; azalea; basswood; white birch; ornamental cherries; red chokeberry; hackberry; Amur honeysuckle; hydrangea; Japanese larch; lespedeza; lilac; saucer magnolia; silver maple; mountain laurel; pear; loblolly pine; mugo pine; red pine; scotch pine; white pine; potentilla; privet; rhododendron; Norway spruce; viburnum (few); yew.
  • Flowers and herbaceous plants: autumn crocus (Colchicum); blue wild indigo (Baptisia); chrysanthemum (some); columbine; hydrangea; lily; narcissus (some); peony (some); petunia; roses; tobacco.
  • Field crops: alfalfa; crimson clover; tobacco.
  • Tip: This does not mean you can't compost black walnut leaves. According to Ohio State University Extension, "walnut leaves can be composted because the toxin breaks down when exposed to air, water and bacteria. The toxic effect can be degraded in two to four weeks." If you do compost the leaves, put them in a separate compost pile and do not spread the resulting compost on plants that are on the sensitive list.
For more information: The go-to book for anyone growing nut and fruit trees in California is the UC Davis publication, The Home Orchard. Add some walnut trees to your property and create a beautiful landscape with these companion plants that tolerate toxicity.

61 comments

  • I have 2.5 acres completely filled with black walnut. The understory is almost entirely Amur honeysuckle, other trees are hackberry, box elder, locust and a couple of white pines.

    The hackberry and Amur honeysuckle are thriving and do not seem walnut sensitive.

    Sarah
  • John, if the leaves start to decompose, then yes they could be adding juglone to your soil. You can rake them up to keep the exposure down. But not much else you can do, other than garden in raised beds, away from the walnut tree.

    Suzanne
  • I have had a 16 by 24’ garden plot for at least 12 years on our side yard with a walnut tree as close as 28’ from the garden. A branch does hang just about over the end of the garden. The first few years the garden was very productive without any issues until juglone began to do a number on especially tomato plants. Had 10 yards of soil removed about five years ago and new soil added after I put down heavy duty black plastic as a barrier against the roots. The garden did great for two or three years and the problem has intensified again. I always clean the garden in the fall by removing dead plants, leaves, etc. before I put down several hundred pounds of manure from a local farmer that raises chickens, steers and some hogs, and other animals for children to visit. Would some leaves laying on the soil for a month or so create the juglone and would possibly puncturing through the soil with some wire tomato holders and wooden stakes also create toxicity from the soil. I have no option to move the garden, but I could add a few raised beds further away from the closest of the two walnut trees. Would appreciate any suggestions in dealing with this ongoing juglone problem. This year it appears to have impacted not only the tomato plants, but also the beans and zucchini plants unless there are other issues do to a spell of heavy rains and then a short heat wave. Thanks.

    John Mellein
  • Do not eat veggies that are growing in the area of a walnut tree. The juglone can be toxic to humans.

    Suzanne
  • Two years, the Black walnut tree in my small backyard and to the left and the right adjoining properties each also a tree.

    First grass yellowed and die
    All of the vegetables got moldy as died
    The Black walnut tree would bloom,drop seeds and then the top drop off where it blooms.
    Can you eat vegetables that Juglone has rained on or roots growing along this tree?

    Gloria wilson
  • Does anyone know if Royal Empress trees are sensitive to the black walnut? I have a tiny little black walnut tree planted and considering relocating it as I have 5 royal empress trees that are about 6’ high. The closest one is about 40’ from the walnut tree.

    Gina Moore
  • Does anyone know if black walnut trees are toxic to succulents? Thanks!

    Kimberly
  • Catherine, roses are sensitive to juglone and I would not recommend putting them near the black walnut tree.

    Suzanne
  • Is there any information regarding different Rose varieties growing near a black walnut. It would be on the south side of my tree, so would receive full sun. In particular, I am wanting to plant some David Austin shrub roses.

    Catherine
  • John, growing the transplant near another black walnut should not be a problem.

    Suzanne
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