Black walnut (Juglans nigra) is considered one of our most valuable native hardwood lumber trees and is often used in large-scale landscapes. In the smaller-scale home landscape, however, the leaves and fruits are considered by some to be a messy nuisance. Furthermore, while many plants can grow well in proximity to a black walnut, the growth of some plant species is thought to be inhibited by this tree.
Black walnuts produce a chemical called juglone, which occurs naturally in all parts of the tree, especially in the buds, nut hulls, and roots. The leaves and stems contain smaller quantities of juglone, which is leached into the soil after they fall. The highest concentration of juglone occurs in the soil directly under the tree’s canopy, but highly sensitive plants may exhibit toxicity symptoms beyond the canopy drip line. Because decaying roots can release juglone, toxicity may occur for several years after a tree has been removed.
Other trees closely related to black walnut, such as butternut, pecan, shagbark hickory, and English walnut also produce juglone, but at concentrations lower than black walnut. Rarely do these trees affect juglone-sensitive plants.
Most toxicity symptoms arise when juglone-sensitive plants are placed within the walnut’s root zone, an average of 50 to 60 feet from the trunk of a large tree. Plants sensitive to juglone may show signs of decline (wilting, yellow leaves, or stunted growth). Many highly sensitive plants can react negatively to even a small concentration of juglone. There are other factors that may impact the health of plants and those should be considered before black walnut toxicity is assumed to be the problem.
The term “allelopathy” refers to the relationship between plants in which one plant produces a substance that inhibits the growth of sensitive plants nearby. It should be noted that although it is ‘known’ as common knowledge in the gardening community, the allelopathic effect of black walnut has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Plants Considered Sensitive to Black Walnut Toxicity
Note that black walnut toxicity due to juglone has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Annuals and vegetables:
- asparagus
- cabbage
- eggplant
- flowering tobacco
- pepper
- petunia
- potato
- tomato
Herbaceous perennials:
- autumn crocus
- baptisia
- columbine
- lily (Asian hybrids)
- peony
- rhubarb
Shrubs:
- blueberry
- red chokeberry
- cotoneaster
- Amur honeysuckle
- hydrangea
- lilac
- privet
- potentilla
- rhododendron
- yew
- some viburnum shrub species
Trees:
- European alder,
- white birch
- crabapple species
- hackberry
- larch
- linden
- saucer magnolia
- mugo pine
- red pine
- white pine
- Norway spruce
- silver maple
- some viburnum tree species
Juglone-sensitive landscape plants should be located away from black walnut trees to avoid damage. Raised beds near trees will help minimize toxicity, but care should be taken to keep leaves, twigs, branches, and nuts out of the bed. Black walnut leaves, bark, and wood chips should not be used as landscape mulch or composted on garden plants. The best alternative is to choose plants from lists of plants thought to be tolerant of juglone.
Trees Considered Tolerant of Black Walnut Toxicity
Note that black walnut toxicity due to juglone has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Tolerant trees are listed alphabetically by their scientific names.
- Boxelder (Acer negundo)
- Japanese maple (Acer palmatum and cultivars)
- Red maple (Acer rubrum)
- Sugar maple (Acer saccharum)
- Ohio buckeye (Aesculus glabra)
- Yellow buckeye (Aesculus octandra)
- Serviceberry (Amelanchier spp.)
- Pawpaw (Asimina triloba)
- Sweet birch (Betula lenta)
- Yellow birch (Betula lutea)
- River birch (Betula nigra)
- American hornbeam (Carpinus caroliniana)
- Hickory (Carya spp.)
- American chestnut (Castanea dentata)
- Southern catalpa (Catalpa bignonioides)
- Redbud (Cercis canadensis)
- Fringe tree (Chionanthus spp.)
- Flowering dogwood (Cornus florida)
- Hawthorn (Crataegus spp.)
- Persimmon (Diospyros virginiana)
- American beech (Fagus grandifolia)
- Honey-locust (Gleditsia triacanthos)
- Silverbell (Halesia carolina)
- Witch-hazel (Hamamelis spp.)
- Sweet-gum (Liquidambar styraciflua)
- Tulip tree (Liriodendron tulipifera)
- Cucumbertree magnolia (Magnolia acuminata)
- Tupelo (Nyssa sylvatica)
- Sycamore (Platanus occidentalis)
- Wild plum (Prunus americana)
- Pin cherry (Prunus pensylvanica)
- Black cherry (Prunus serotina)
- White oak (Quercus alba)
- Scarlet oak (Quercus coccinea)
- Shingle oak (Quercus imbricaria)
- Northern red oak (Quercus rubra)
- Black oak (Quercus velutina)
- Staghorn sumac (Rhus typhina)
- Black locust (Robinia pseudoacacia)
- Willow (Salix spp.)
- Sassafras (Sassafras albidum)
- American elm (Ulmus americana)
- Slippery elm (Ulmus rubra)
Shrubs Considered Tolerant of Black Walnut Toxicity
Note that black walnut toxicity due to juglone has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Tolerant shrubs are listed alphabetically by their scientific names.
- Devil’s walking stick (Aralia spinosa)
- New Jersey tea (Ceanothus americanus)
- Fringe tree (Chionanthus virginicus)
- Pagoda dogwood (Cornus alternifolia)
- Silky dogwood (Cornus amomum)
- American hazelnut (Corylus americana)
- February daphne (Daphne mezereum)
- Forsythia (Forsythia spp.)
- Rose-of-Sharon (Hibiscus syriacus)
- Wild hydrangea (Hydrangea arborescens)
- Shrubby St. John’s wort (Hypericum prolificum)
- Juniper (Juniperus spp.)
- Beauty bush (Kolkwitzia amabilis)
- Spicebush (Lindera benzoin)
- Mock-orange (Philadelphus spp.)
- Ninebark (Physocarpus opulifolius)
- Exbury rhododendron (Rhododendron hybrids)
- Fragrant sumac (Rhus aromatica)
- Shining sumac (Rhus copallina)
- Smooth sumac (Rhus glabra)
- Currant (Ribes spp.)
- Wild rose (Rosa spp.)
- Black raspberry (Rubus occidentalis)
- Purple-flowering raspberry (Rubus odoratus)
- Elderberry (Sambucus spp.)
- American bladdernut (Staphylea trifolia)
- Maple-leaved viburnum (Viburnum acerifolium)
- Korean spice viburnum (Viburnum carlesii and cultivars)
- Southern arrowwood (Viburnum dentatum)
- Black-haw (Viburnum prunifolium)
- Yucca (Yucca spp.)
- Prickly-ash (Zanthoxylum americanum)
Evergreens Considered Tolerant of Black Walnut Toxicity
Note that black walnut toxicity due to juglone has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Listed by common name (Scientific name)
Chinese juniper (Juniperus chinensis)
Common juniper (Juniperus communis)
Eastern red cedar (Juniperus virginiana)
Arborvitae (Thuja spp.)
Eastern hemlock (Tsuga canadensis)
Vines Considered Tolerant of Black Walnut Toxicity
Note that black walnut toxicity due to juglone has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Trees are listed alphabetically by their scientific names.
- Dutchman’s pipe (Aristolochia durior)
- Bittersweet (Celastrus spp.)
- Clematis (Clematis ssp.)
- Honeysuckle vine (Lonicera spp.)
- Virginia creeper (Parthenocissus quinquefolia)
- Greenbriar (Smilax spp.)
- Wild grape (Vitis spp.)
- Wisteria (Wisteria spp.)
Herbaceous Perennials, Spring Wildflowers, and Bulbs Considered Tolerant of Black Walnut Toxicity
Note that black walnut toxicity due to juglone has not been studied in depth. Much of what is known is based on one study done many decades ago. This means that any list regarding this topic is incomplete and some of the information may be anecdotal.
Tolerant perennials are listed alphabetically by their scientific names.
- Yarrow (Achillea spp.)
- Bugleweed (Ajuga spp.)
- Hollyhock (Alcea rosea)
- Windflower (Anemone spp.)
- Jack-in-the-pulpit (Arisaema triphllyum)
- Wild ginger (Asarum spp.)
- Aster (Aster spp.)
- Astilbe (Astilbe spp.)
- Lady fern (Athyrium spp.)
- Rattlesnake fern (Botrychium spp.)
- Bellflower (Campanula spp.)
- Toothwort (Cardamine spp.)
- Chrysanthemum (Chrysanthemum spp.)
- Spring beauty (Claytonia virginica)
- Fragile fern (Cystopteris fragilis)
- Leopard’s bane (Doronicum spp.)
- Wood fern (Dryopteris spp.)
- Purple coneflower (Echinacea purpurea)
- Epimedium (Epimedium spp.)
- Winter aconite (Eranthis hyemalis)
- Dog’s tooth violet (Erythronium spp.)
- Joe-pye weed (Eupatorium spp.)
- Snowdrop (Galanthus nivalis)
- Sweet woodruff (Galium odoratum)
- Gentian (Gentiana spp.)
- Cranesbill (Geranium spp.)
- Perennial sunflower (Helianthus spp.)
- Hellebore (Helleborus spp.)
- Daylily (Hemerocallis spp.)
- Coral bell (Heuchera spp.)
- Hosta (Hosta spp.)
- Virginia waterleaf (Hydrophyllum virginianum)
- Siberian iris (Iris sibirica)
- Bleeding heart (Lamprocapnos spectabilis)
- Bush-clover (Lespedeza spp.)
- Lilyturf (Liriope spp.)
- Lobelia (Lobelia spp.)
- Peppermint (Mentha piperita)
- Bee balm (Monarda spp.)
- Grape hyacinth (Muscari spp.)
- Daffodil selected (Narcissus spp.)
- Evening primrose (Oenothera spp.)
- Sensitive fern (Onoclea sensibilis)
- Cinnamon fern (Osmunda cinnamomea)
- Summer phlox (Phlox paniculata)
- False dragonhead (Physostegia virginiana)
- Mayapple (Podophyllum peltatum)
- Jacob’s ladder (Polemonium reptans)
- Solomon’s seal (Polygonatum spp.)
- Christmas fern (Polystichum spp.)
- Primrose (Primula spp.)
- Lungwort (Pulmonaria spp.)
- Buttercup (Ranunculus spp.)
- Black-eyed Susan (Rudbeckia spp.)
- Bloodroot (Sanguinaria canadensis)
- Siberian squill (Scilla sibirica)
- Stonecrop (Sedum spp.)
- Goldenrod (Solidago spp.)
- Lamb’s ears (Stachys byzantina)
- Meadow rue (Thalictrum spp.)
- Spiderwort (Tradescantia virginiana)
- Trillium (Trillium spp.)
- Tulip selected (Tulipa spp.)
- Bellwort (Uvularia spp.)
- Speedwell (Veronica spp.)
- Violet (Viola spp.)