Lavandula Girl
July 11th, 2006, 10:36 PM
After mentioning an article on Black Walnut effects that I wrote for the local paper, I was PM'd by several members asking to read it. Please understand that this was intended as an educational tool for people who were unfamiliar with juglone poisoning, not as an in-depth scientific document. Hopefully, this will be of help to some of you!
Black Walnut trees (Juglans nigra L.) are not uncommon in Page County; many of us have them in our yards. These trees are valuable for their edible nuts, and also for their beautiful hardwood. As a landscape specimen, however, their attraction as a large shade tree is tempered by their ability to kill off much of what we attempt to plant under them.
Allelopathy is the relationship between two plants, where one produces a substance that affects the growth of the other. Black Walnuts produce juglone (5 hydroxy-1, 4-napthoquinone), a chemical which causes foliar yellowing, wilting, and death in other plants. In experiments done by several universities, including Purdue, juglone has been shown to be a respiratory inhibitor in plants. This means that it deprives them of needed energy, and prevents metabolic activity. This allelopathic event is often referred to as juglone poisoning, or walnut wilt. All parts of a Black Walnut produce juglone, so as gardeners we need to work with the trees rather than against them. Even cutting down the walnut won’t work, as studies show that their subterranean root system continues to release juglone into the soil for years after the tree is taken down. Further complicating the struggle, juglone concentrations are dependent on soil drainage, and many of us are already aware of the clay prevalent in our area. Poorly draining clay helps hold the chemical in our yards, exacerbating the problem.
So what can we do to make the area under our walnut trees attractive? Luckily, there are a few plants that will thrive in the presence of Black Walnuts. By planning carefully, we can establish beds that bring color and fragrance into our yards. Here are some suggestions for gardens that can be cultivated in the canopy of these trees, along with partial plant lists. More extensive plant lists can be obtained at many Internet sites devoted to the subject of walnut wilt, including plantclinic.cornell.edu and wvu.edu/~agexten.
FOR A FRAGRANT GARDEN BED:Galium odoratum (sweet woodruff) Monarda didyma (bee balm)Monarda fistula (wild bergamot) Hyacinth var. Tulipa var. Lonica tartarica (tartartian honeysuckle)
FOR SHOWY BLOOM: Alcea rosea (hollyhock) Campanula latifolia (bellflower) Chrysanthemum var. Hemerocallis fulva (common daylily) Iris siberica (Siberian Iris) Narcissus var. (daffodils) Forsythia suspensa (weeping forsythia)
FOR A SHADE GARDEN: Araceae var. (jack-in-the-pulpit) Asarum europaeum (wild ginger) Dicentra var. (bleeding heart) Hosta var. Onoclea sensibilis (sensitive fern) Osmunda cinnommea (cinnamon fern) Tradescantia virginiana (spiderwort) Begonia var. (begonia, fibrous and tuberous)
There are also a variety of trees that will thrive under a Black Walnut, including Acer palmatum (Japanese maple), Hibiscus syriacus (Rose of Sharon) and Quercus var. (oak). As to what doesn’t grow, the list is quite long. Avoid planting azaleas, mountain laurel, and other plants in the Rhododendron family. Peonies have managed to show up on both the list that does and the list that does not thrive, so if you’ve spent some money on that cultivar, I wouldn’t plant it under a Black Walnut if I were you! The same can be said for lilac and crabapple. If you are a vegetable gardener, avoid planting anything in the nightshade family near a Black Walnut, (tomatoes, potatoes, peppers, and eggplant) or anything in the cole family (cabbage, cauliflower, Brussels sprouts, and broccoli). These veggies can be grown with excellent results in containers. If your kitchen garden is quite close to a Black Walnut, sow your beans, beets, carrots and corn in the ground, and intersperse with containers filled with the more sensitive plants. By keeping the containers free of tree detritus like leaves and nuts, you can get nice results.
In terms of that tree detritus, make sure you clear the leaves and nuts from you yard. Most grasses do a marginal job of growing under a walnut, and you can help you lawn quite a bit if you clean up after your tree. Remember not to mulch using Black Walnut leaves or nut hulls, and if you add clippings or leaves to you compost, bury them deep and make sure they are fully composted (unrecognizable) before using. Finally, while Black Walnut produces the most virulent juglone poisoning, the same effects can be seen to a lesser degree involving it’s relatives: Butternut, English Walnut, Shagbark Hickory, Pecan, and Bitternut Hickory. If you have plant die off occurring near these trees, you may well have to reconsider what you are putting near them.
Black Walnut trees (Juglans nigra L.) are not uncommon in Page County; many of us have them in our yards. These trees are valuable for their edible nuts, and also for their beautiful hardwood. As a landscape specimen, however, their attraction as a large shade tree is tempered by their ability to kill off much of what we attempt to plant under them.
Allelopathy is the relationship between two plants, where one produces a substance that affects the growth of the other. Black Walnuts produce juglone (5 hydroxy-1, 4-napthoquinone), a chemical which causes foliar yellowing, wilting, and death in other plants. In experiments done by several universities, including Purdue, juglone has been shown to be a respiratory inhibitor in plants. This means that it deprives them of needed energy, and prevents metabolic activity. This allelopathic event is often referred to as juglone poisoning, or walnut wilt. All parts of a Black Walnut produce juglone, so as gardeners we need to work with the trees rather than against them. Even cutting down the walnut won’t work, as studies show that their subterranean root system continues to release juglone into the soil for years after the tree is taken down. Further complicating the struggle, juglone concentrations are dependent on soil drainage, and many of us are already aware of the clay prevalent in our area. Poorly draining clay helps hold the chemical in our yards, exacerbating the problem.
So what can we do to make the area under our walnut trees attractive? Luckily, there are a few plants that will thrive in the presence of Black Walnuts. By planning carefully, we can establish beds that bring color and fragrance into our yards. Here are some suggestions for gardens that can be cultivated in the canopy of these trees, along with partial plant lists. More extensive plant lists can be obtained at many Internet sites devoted to the subject of walnut wilt, including plantclinic.cornell.edu and wvu.edu/~agexten.
FOR A FRAGRANT GARDEN BED:Galium odoratum (sweet woodruff) Monarda didyma (bee balm)Monarda fistula (wild bergamot) Hyacinth var. Tulipa var. Lonica tartarica (tartartian honeysuckle)
FOR SHOWY BLOOM: Alcea rosea (hollyhock) Campanula latifolia (bellflower) Chrysanthemum var. Hemerocallis fulva (common daylily) Iris siberica (Siberian Iris) Narcissus var. (daffodils) Forsythia suspensa (weeping forsythia)
FOR A SHADE GARDEN: Araceae var. (jack-in-the-pulpit) Asarum europaeum (wild ginger) Dicentra var. (bleeding heart) Hosta var. Onoclea sensibilis (sensitive fern) Osmunda cinnommea (cinnamon fern) Tradescantia virginiana (spiderwort) Begonia var. (begonia, fibrous and tuberous)
There are also a variety of trees that will thrive under a Black Walnut, including Acer palmatum (Japanese maple), Hibiscus syriacus (Rose of Sharon) and Quercus var. (oak). As to what doesn’t grow, the list is quite long. Avoid planting azaleas, mountain laurel, and other plants in the Rhododendron family. Peonies have managed to show up on both the list that does and the list that does not thrive, so if you’ve spent some money on that cultivar, I wouldn’t plant it under a Black Walnut if I were you! The same can be said for lilac and crabapple. If you are a vegetable gardener, avoid planting anything in the nightshade family near a Black Walnut, (tomatoes, potatoes, peppers, and eggplant) or anything in the cole family (cabbage, cauliflower, Brussels sprouts, and broccoli). These veggies can be grown with excellent results in containers. If your kitchen garden is quite close to a Black Walnut, sow your beans, beets, carrots and corn in the ground, and intersperse with containers filled with the more sensitive plants. By keeping the containers free of tree detritus like leaves and nuts, you can get nice results.
In terms of that tree detritus, make sure you clear the leaves and nuts from you yard. Most grasses do a marginal job of growing under a walnut, and you can help you lawn quite a bit if you clean up after your tree. Remember not to mulch using Black Walnut leaves or nut hulls, and if you add clippings or leaves to you compost, bury them deep and make sure they are fully composted (unrecognizable) before using. Finally, while Black Walnut produces the most virulent juglone poisoning, the same effects can be seen to a lesser degree involving it’s relatives: Butternut, English Walnut, Shagbark Hickory, Pecan, and Bitternut Hickory. If you have plant die off occurring near these trees, you may well have to reconsider what you are putting near them.