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Black Walnuts and some other closely related species of trees produce a chemical called juglone. This can be found in all parts of the tree including the roots, leaves, and in the hulls of its fruit. Black Walnuts produce a very high concentration of juglone relative to the other species of plants. This can affect and even kill many species of plants that attempt to grow in their vicinity. Plants sensitive to juglone should be placed at a minimum of 50-60 feet from the trunk of a mature black walnut tree. If you are planting near large black walnuts, it is important to select landscape that is tolerant of juglone, since there is no way to cure plants once they start to decline in health.

TREES

  • 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 
  • Honey-locust (Gleditsia triacanthos)
  • Silverbell (Halesia carolina)
  • Witch-hazel (Hamamelis spp.)
  • Sweet-gum (Liquidambar styraciflua)
  • Tulip tree (Liriodendron tulipifera)
  • Cucumbertree (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)

EVERGREENS

  • Chinese juniper (Juniperus chinensis)
  • Common juniper (Juniperus communis)
  • Eastern red cedar (Juniperus virginiana)
  • Arborvitae (Thuja spp.)
  • Eastern hemlock (Tsuga canadensis)

SHRUBS

  • 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)

VINES

  • Dutchman’s pipe (Aristolochia durior)
  • Bittersweet (Celastrus spp.)
  • Clematis (Clematis ssp.)
  • Honeysuckle vine (Lonicera spp.)
  • Virginia creeper (Parthenocissus spp.)
  • Greenbriar (Smilax spp.)
  • Wild grape (Vitis spp.)
  • Wisteria (Wisteria spp.)

PERENNIALS

  • 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.)
  • Chrysanthemum (Chrysanthemum spp.)
  • Spring beauty (Claytonia spp.)
  • Fragile fern (Cystopteris fragilis)
  • Toothwort (Dentaria spp.)
  • Bleeding heart (Lamprocapnos spctabilis)
  • 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)
  • 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 spp.)
  • 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.)

Information gathered by Wasco Nursery’s team of experts, along with the help of the Morton Arboretum.

https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/black-walnut-toxicity/#overview