Juglone, Walnuts, and Pecans Oh My! 3


Do you have a Walnut or Pecan tree? Does most of what you plant under and near it end up dying?

This is because this family of trees produce an allelopathic chemical called Juglone. Juglone is an organic compound that stunts the growth of many plants by inhibiting enzymes that are needed for metabolism, essentially starving them to death. This gives these trees a competitive advantage, but it can be aggravating for the local gardener. Luckily, there are many plants and trees, mostly those native to the same areas, that can thrive despite the presence of this chemical.

Juglone is produced by trees in the Juglandaceae family (AKA walnut).

Plants that produce Juglone
Common Name Latin Name Amount of Juglone
Black Walnut Juglans nigra High
Butternut (white walnut) Juglans cinerea High
English Walnut (Persian or Common walnut) Juglans regia Medium
Pecan Carya illinoinensis Low
Hickory Carya (genus) Medium-low

 

Reducing the impact of juglone on surrounding plants

Juglone can affect an area of 50-80ft around the tree depending on the root zone and the radius of the canopy. Juglone is found in increasing amount from leaves, bark, wood, roots, and hulls with hulls having the highest concentration.

Walnut trimmings can be composted (though it is not recommended) since juglone will break down when exposed to water, air and soil bacteria. The time it takes to break down varies, but leaves take 2-4 weeks when composted. In soil it can take as little as 2 months, though it’s recommended to give the materials 6 months minimum to break down for use around sensitive plants. Compost can be tested for juglone by planting a sensitive plant (tomato) in the compost and observing how and if it grows.

  • Other methods you can use are: Build raised beds to give a greater separation from the toxin.
  • Remove leaves, hulls, and stems from surrounding area.
  • Plant a buffer zone to reduce contact with juglone.

Below we have a list of trees, shrubs, and plants and their tolerance/intolerance of juglone, based on our research. We will add to it as we experiment with more! Please comment or contact us if you have anything to add!

 

Plants Tolerant of Juglone

Plants That Do Not Grow Within the Drip Line of Black Walnut

*Cultivars of some species may survive but will do poorly.

Trees Tolerant to Juglone

Trees Intolerant to Juglone

Arborvitae (Thuja occidentalis) Alder, European (Alnus glutinosa)
Beech, American (Fagus grandifolia) Apples and Crabapples (Malus spp)
Black Gum (Nyssa sylvatica) Basswood (Tilia heterophylla)
Black Locust (Robinia pseudoacacia) Birches, White (Betula species)
Blackhaw Viburnum (Viburnum prunifolium) Hackberry, Northern (Celtis occidentalis)
Canada Hemlock (Tsuga Canadensis) Maple, Silver (Acer saccharinum)
Carolina Silverbell (Halesia caroliniana) Pine, Eastern White (Pinus strobus)
Catalpa (Catalpa bignoniodes) Pine, Red (Pinus resinosa)
Cherry (Prunus spp) Pine, Mugo (Pinus mugo)
Cherry, Black (Prunus serotina) Spruce, Norway (Picea abies)
Dogwood (Cornus alternifolia)
Dogwood, Flowering (Cornus florida)
Eastern Red Cedar (Juniperus virginiana)
Eastern Redbud (Cercis canadensis)
Elm, American (Ulmus americana)
Fringetree (Chionanthus spp.)
Goldenrain Tree (Koelreuteria paniculata)
Hackberry
Hawthorne (Crataegus spp)
Hickory (Carya spp)
Honeylocust (Gleditsia triacanthos)
Maple (except silver maple) (Acer spp)
Nectarine (Prunus spp)
Oak species (Quercus spp)
Ohio Buckeye (Aesculus glabra)
Pawpaw (Asimina triloba)
Peach (Prunus spp)
Pear, Callery (Pyrus calleryana)
Persimmon (Diosypros virginiana)
Plum (Prunus spp)
Quince (Cydonia oblongata)
River Birch (Betula nigra)
Sassafras (Sassafras albidum)
Serviceberry, Shadblow (Amelanchier)
Staghorn Sumac (Rhus typhina)
Sweetgum (Liquidambar styraciflua)
Sycamore (Platanus occidentalis)
Virginia Pine (Pinus virginiana)
White Ash (Fraxinus americana)
Yellow Poplar (Liriodendron tulipifera)

Shrubs and Vines Tolerant to Juglone

Shrubs and Vines Intolerant to Juglone

Arborvitaes (Thuja species)
American Holly (Ilex opaca) Blackberry (Rubus allegheniensis)
Barberry (Berberis spp) Blueberry (Vaccinium corymbosum)
Bittersweet Brush Cinquefoil (Potentilla spp)
Black Raspberry (Rubus occidentalis) Chokeberry, Red (Aronia arbutifolia)
Clematis (Clematis spp) Cotoneaster
Current (Ribes spp) Honeysuckle, Amur (Lonicera maackii)
Daphne (Daphne spp) Hydrangea (spp)
Elderberry (Sambucus Canadensis) Lilacs (Syringa spp and cultivars)
Euonymus (Euonymus spp) Mountain Laurels (Kalmia spp)
Exbury Hybrid Azalea “Gibraltar” & “Balzac” Privet (Ligustrum spp)
Forsythia (Forsythia spp) Rhododendrons and Azaleas, **Rhododendron species (most)
Gibraltar’ and ‘Balzac’, Rhododendron Exbury hybrids ** Viburnum plicatum tomentosum ‘Mariesii’ *
Greenbrier Yew (Taxus spp)
Hazelnut (Corylus americana)
Honeysuckle (most Lonicera spp)
Hydrangea, Snowball (Hydrangea arborescens)
Juniper (Juniperus spp)
Mockorange (Philadelphus spp)
Pachysandra
Pinxterbloom Azalea (Rhododendron periclymenoides) **
Rose of Sharon (Hibiscus syriacus)
Rose, Multiflora (Rosa multiflora)
Rose, Wild
Spicebush (Lindera benzoin)
Sumac (Rhus copallina)
Sumac, Smooth (Rhus glabra)
Viburnum (Most Viburnum spp) **
Virginia Creeper (Parthenocissus quinquefolia)
Wild Grape (Vitis)
Willow
Wisteria (Wisteria spp)
Witchhazel (Hamamellis spp)

Herbaceous Plants Tolerant to Juglone

Herbaceous Plants Intolerant to Juglone

Anemone (Anemone spp)
Aster (Aster spp) Alfalfa, Medicago sativa
Astilbe (Astilbe spp) Asparagus, Asparagus offinalis
Balms (Monarda spp) Autumn Crocus
Begonia (Begonia) Baptisia australis
Bellflower (Campanula latifolia) Buttercup, Narcissus ‘John Evelyn,’ ‘Unsurpassable’ ‘King Alfred’ and ‘Ice Follies’
Big Merrybells (Uvularia grandiflora) Cabbage (Brassica oleracea capitata)
Black-eyed Susan Chrysanthemum (Chrysanthumum spp (some))*
Bleeding Heart (Dicentra spp) Columbine, Colorado (Aquilegia caerulea)
Bloodroot (Sanguinaria canadensis) Columbine, Wild (Aquilegia canadensis)
Bluebell, Virginia (Mertensia pulmonariodes) double-flowered cole vegetables
Bugleweed (Ajuga reptans) Eggplant (Solanum melongena)
Calendula Forget-me-not
Christmas Fern (Polystichum acrostichoides) Lilies, Lilium species (particularly the Asian hybrids)
Christmas Rose (Helleborus spp) Peonies (Paeonia species (some))*
Chrsyanthemum (Chrysanthemum spp) ** Peppers (Capsicum spp) (some)
Cicely (Myrrhis odorata) Petunia species and cultivars
Cinnamon Fern (Osmunda cinnamomea) Potato (Solanum tuberosum)
Clover, White Rhubarb (Rheum rhabarbarum)
Coral Bells (Heuchera spp) Tobacco (Nicotiana alata)
Crocus (Crocus spp) Tomatoes (Lycopersicon esculentum)
Daffodil (Narcissus spp)
Daylily (Hemerocallis spp)
Dutchman’s Breeches (Dicentra cucullaria)
Epimedium (Epimedium spp)
European Wild Ginger (Asarum europaeum)
Fern, Crested Wood (Dryopteris cristata)
Ferns
Gentian (Gentian spp)
Geranium, Cranesbill (Geranium sanguineum)
Globeflower (Trollius spp)
Glory of the Snow (Chionodoxa lucilae)
Goldmoss Stonecrop (Sedum acre)
Grasses (most) (Gramineae family)
Grasses Kentucky bluegrass (Poa pratensis L.)
Herb Robert (Geranium robertianum)
Hollyhock (Alcea rosea)
Hosta (Hosta spp)
Hyacinth, Common (Hyacinthus Orientalis)
Hyacinth, Grape (Muscari botryoides)
Iris (Iris spp)
Jack-in-the-Pulpit (Arisaema triphyllum)
Jacob’s Ladder (Polemonium reptans)
Jerusalem Artichoke (Helianthus tuberosus)
Lamb’s Ear (Stachys byzantia)
Leopard’s Bane (Doronicum spp)
Liriope or Lilyturf (Lirope spp)
Lobelia (Lobelia spp)
Lungwort (Pulmonaria spp)
Mayapple (Podophyllum peltatum)
Meadowrue (Thalictrum spp)
Morning Glory (Ipomoea spp)
Orange Hawkweed (Hieracium auranticum)
Pansy (Viola spp)
Peony, **Paeonia species (some)
Phlox (Phlox paniculata)
Plantain-lily, Hosta fortunei ‘Glauca’
Pot Marigold (Calendula officinalis)
Primrose (Primula spp)
Purple Coneflower (Echinacea purpurea)
Sedum, Showy (Sedum spectabile)
Sedum, Stonecrop (Sedum acre)
Senstitive Fern (Onoclea sensibilis)
Shasta Daisy (Leucanthemum x superbum)
Siberian Iris (Iris sibirica)
Siberian or Blue Squill (Scilla siberica)
Siberian Squill (Scilla sibirica)
Snowdrop (Galanthus nivalis)
Solomon’s Seal (Polygonatum commutatum)
Spanish Bluebell (Hyacinthoides hispanicus)
Spiderwort (Tradescantia virginiana)
Spring Beauty (Claytonia virginica)
St. John’s Wort (Hypericum spp)
Sundrops (Oenothera spp)
Sunflower (Helianthus spp)
Sweet Woodruff (Galium odoratum)
Trillium (Trillium spp)
Tulips (Tulipa spp)
Violet (Viola spp)
Violet, Dog’s Tooth (Erythronium spp)
Virginia Waterleaf (Hydrophyllum virginianum)
Wheat
Wild Bergamot (M. fistulosa)
Winter Aconite (Eranthis hyemalis)
Yarrow (Achillea spp)
Zinnia (Zinnia spp)

Vegetables Tolerant to Juglone

Vegetables Intolerant to Juglone

Beans  Asparagus
Beets  Cabbage and other Cruciferous Vegetables
Carrot  All edible nightshades- Tomatoes, Peppers, Eggplant, Potatoes
Corn
Melons
Onion
Parsnips
Squash

 

Resources
OSU – Black Walnut Toxicity…
Penn State – Landscaping around walnuts…


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