Walnut trees (walnut juglans or Black walnut juglans nigra) are fruitful and beautiful. I love to sit in the shade of one of my English walnut trees and look out over the sloping garden. In our video Tricia shows you how to care for and prune walnut trees.
Walnut trees are native to North America. They are large and can grow to over 100 feet tall and are great shade trees. These 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 toxicityBlack walnut trees load their roots, buds, and nut hulls (covering walnut fruits) 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 walnut 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, peppers, potatoes, rhubarb, tomatoes.
- 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.
Paul, I am not sure of the sensitivity to juglone in hay or cover crops. This would be a good question for your local Ag Extension contact.
I have access to large quantities of black walnut hulls and want to dispose of them in an efficient and responsible manner. Are there any field/hay crops that are tolerant of walnut hulls that are spread on a field? If the hulls were spread on a field, would they adversely affect the Ph of the soil?
Joy, if your trees were cut down 4 years ago, you should be fine to plant in the area. Juglone breaks down after about a year.
We have four black walnut stumps (from what were mature trees) that have been dormant for about four years. Will we be able to grow tomatoes and other veggies in raised beds in their vicinity? We did encounter root systems when digging out soil to place a raised bed.
Jodi, take a look at the articles linked in the blog. If they are not listed in the articles, then you may need to do some additional research online to find out if they are sensitive.