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WALNUT TOXICITY

Black walnut roots release a toxin called Juglose that prevents many plants from growing. Plants that are susceptible to the toxicity and usually die slowly (by gradually wilting) include:
          Tomato
          Alfalfa
          Pear
          Blackberry
          Red Pine
          Blueberry
          Mountain Laurel
          Azaleas
          Rhododendron
          Potentilla
          White Pine
Other evergreens may be affected.

To avoid injury, susceptible plants should be place at least eight feet past the walnut tree's dripline.

Walnut sawdust or wood chips have been shown to affect plants in a similar fashion and should not be used as a mulch around these plants.
 

PERENNIAL PLANTS NOT AFFECTED

The following is a list of herbaceous perennial plants that appear NOT affected by the toxicity relased by walnut roots.

Ajuga reptans (bugle weed)    Monarda didyma (Bee balm)
Alcea rosea (Hollyhock)       Monarda fistulosa (Wild bergamot)
Asarum europeaeum (European wild ginger)
Oenothera frutcosa (Sundrops)
Osmunda cinnamomea (Cinnamon fern)
Astilbe                       Phlox paniculata (Summer phlox)
Camnpanula latifolia (Bellflower)Polemonium reptans (Jacob's ladder)
Chyrsanthemums                Polygonatum commutatum (Great
Doronicum (Leopard's bane)         Solomon's Seal)
Dryopteris cristata (Crested Wood fern)Primula X polyantha (Polyanthus Galium
Galium odoratum (Sweet woodruff)   Primrose)
Geranium robertianum (herb Robert)Pulmonaria (Lungwort)
Geranium sanguineum (Cranesbill)Sanguinaria canadensis (Bloodroot)
Helianthus tuberosus (JerusalemSanguinaria canadaensis 'Multiplex'
     artichoke)                    (Double flowered bloodroot)
Hemerocallis (Daylily)        Sedum acre (Gold moss)
Heuchera X brizoides ('Pluie de Feu'Sedum spectabile 
     Coral Bells)             Stachys byzantina (Lamb's Ear)
Hieracium aurantiacum (Orange Tradescantia virginiana (Spiderwort) 
     Hawkweed)                Trillium cernuum (Nodding trillium)
Hosta fortunei                Trillium grandiflorum (White Wake-
Hosta lancifolia                   Robin, Trillum)
Hosta marginata               Uvularia grandiflora (Big merrybells)
Hydrophyllum virginianum (VirginiaViola canadensis (Canada Violet)
     waterleaf)               Viola sororia (Woody blue violet)
Iris sibirca (Siberian Iris)
 
ANNUALS NOT AFFECTED
The following is a partial list of annual flowers that appear NOT affected by the toxicity released by walnut roots.
     Begonia (fibrous rooted)
     Calendulas
     Morning Glory
     Horned Violet
     Pansy
TREES NOT AFFECTED
The following is a partial list of trees that appear NOT affected by the toxicity released by walnut roots.
  Acer palmatum (Japanese Maple) Acer plamatum 'Dissectum' (Cutleaf Japanese Maple) Catalpa bignonioides (Common Catalpa) Tsuga canadensis (Canadian hemlock) 
VINES/SHRUBS NOT AFFECTED
The following is a partial list of vines and shrubs that appear NOT affected by the toxicity released by walnut roots.
  Clematis Daphne Forsythia Hibiscus Rose-of-Sharon Tartarian Honeysuckle Virginia Creeper Rhododendron Exbury hybrids 
WEEDS NOT AFFECTED
The following is a partial list of weeds that appear NOT affected by the toxicity released by walnut roots.
  Glechoma hederacea (Ground Ivy, Creeping Charlie) Oxalis corniculata (Creeping sorrel) Stellaria media (Chickweed) Taraxacum officinale (Dandelion) Veronica filiformis (Veronica speedwill) 
BULBS AND BULBOUS PLANTS NOT AFFECTED

The following is a list of bulbs and bulbous plants that appear NOT affected by the toxicity released by walnut roots.

     Chionodoxa (Glory-of-the-snow)
     Crocus
     Endymion (Spanish Bluebells)
     Eranthis (Winter Aconite)
     Galanthus (Snowdrop)
     Hyacinths
     Muscari (Grape Hyacinths)
     Narcissus (Daffodils)
     Scilla (Blue Squill)
     Tulips


See also Walnuts section in Mulch

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