When I moved in to my first home, I was so eager to start creating my backyard garden. I knew from talking with the former owner that our property line included black walnut trees, which I was told were desirable by loggers because of their straight trunks. The trees were healthy, so to me, they blended in to the background.
I had no idea that black walnut trees have juglone, which is present in their roots, leaves and nut hulls. Technically speaking, this is a type of allelopathy, which is a survival technique that some plants have developed to reduce competition of nearby plants by stunting growth and germination. This can even kill certain varieties of plants. (More info on that, here.)
I lost a good amount of plants in the first few years because I didn't do my research. It wasn't until I started researching the symptoms of what I was seeing as the plants declined (the tomatoes were the most dramatic of the bunch!), that I found out about black walnut toxicity.
Living with black walnut trees
Black walnut trees (Juglans nigra) grow in USDA zones 4-9, and can reach 50-75 feet (15.24-22.86 meters)!
I've tried to turn my original negative experiences with the black walnut trees into positives. The tall trees do attract songbirds and woodpeckers. The tree is said to host 23 species of moths, including dagger moths, luna moths, and walnut caterpillar moths, which then attracts chickadees, bluebirds, nuthatches, wrens, according to Grimm's Gardens.
"There is little scientific research done to determine whether plants can thrive in the presence of black walnut and partially because so much of whether a plant can tolerate black walnuts depends on growing conditions," explained Stacey Hirvela, Proven Winners shrub specialist. "For example, a well-watered plant will fare better than one that does not get irrigated. Rich soils with lots of organic matter make it easier for plants near black walnut than very dry, rocky soils."
Garden maintenance is also important. When I find pieces of husks in garden beds, I dispose of them. (Sometimes I'll leave the fully enclosed nuts in a designated area for squirrels to eat.) I do not compost them.
"Many scientists believe that it is primarily the leaves and fruits being left on the ground when they drop in fall that makes a difference, so if you are vigilant about cleaning up after your plants in fall, your plants will do much better than those that are just left with everything falling where it may," confirmed Hirvela.
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| In the Northeast U.S. in mid-July, the black walnut tree begins to form lime-green fruit. They will ripen by October and can be as large as a baseball, and will begin to fall to the ground. |
It is much easier to incorporate black walnut tolerant varieties in the garden than I originally thought, and as a result I've discovered a wide range of plants I would not have previously tried growing.
Some plants are new to me, including Lamium maculatum, a perennial that Darwin Perennials recommends pairing near black walnut trees. Its flowers are purple, pink and white, with foliage that varies between green and silver. It ranges in size between 4 to 12 inches (10-30 cm), depending on the variety.
Another colorful perennial foliage option is Heuchera, such as Darwin Perennials' Heuchera 'Carnival Burgundy Blast' and Proven Winners' 'Dolce Toffee Tart' (the latter which I'm trialing in my back garden this season). For flowering groundcovers, Darwin Perennials also recommends Lysimachia congestiflora 'Firefly' which combines burgundy foliage with bright yellow flowers for shady areas.
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| Lysimachia congestiflora 'Firefly'; image courtesy of Darwin Perennials. |
For larger varieties, I reached out to Natalie Carmolli of Spring Meadow Nursery, Inc., Proven Winners® ColorChoice® Shrubs, for recommended shrub and small tree cultivars that will tolerate the black walnut.
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| Sunny Boulevard® St. John’s-Wort; image courtesy of Proven Winners ColorChoice Shrubs. |
Carmolli recommended five assorted options to consider:
- Show Off® Sugar Baby Forsythia — this dwarf forsythia sports yellow flowers in the spring and is deer resistant.
- Golden Shadows® Cornus alternifolia — this dogwood will reach between 10-12 feet (3-3.6 meters), and sports large heart-shaped leaves that are bright yellow, with an irregular green "thumbprint".
- Sunny Boulevard® St. Johns-Wort — this native plant is deer resistant and its yellow flowers are attractive to pollinators.
- Illuminati Arch® Mock Orange or Illuminati Tower™ Mock Orange — offers fragrant white flowers in early summer.
- Montana Moss® Juniper — this blue-green evergreen groundcover spreads 3 to 5 feet (0.9-1.5 meters).
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| Digitalis "Arctic Fox Rose" grows close to my black walnut trees. |
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| Coleus adds pops of color in shady areas near black walnut trees. This is "Alabama Sunset." |
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| Feverfew grows well near black walnut trees. |
Here's what has survived in my garden to date
Here are plants that I have had success growing in my garden (in no particular order):
- Elderberry (get the fruit before the birds do)
- Spice bush (host plant to spicebush swallowtail butterflies)
- 'Green Giant' Thuja (Thuja standishii x plicata)
- Daylilies (info on how to grow, here)
- Daffodils
- Tulips
- Hellebores (poisonous)
- Solomon's Seal
- Wild Ginger
- Bleeding Heart
- Dogtooth violet (yellow trout lily)
- Phlox Paniculata (tall phlox)
- Coleus
- Foxglove (such as Digitalis "Arctic Fox Rose", a trial plant I received from Darwin Perennials in 2020; poisonous)
- Snowdrops
- Crocus
- Winter aconite
- Rose-of-Sharon (Hibiscus syriacus)
- Clematis
- Ferns
- Native celandine
- Asters
- Hostas
- White forsythia
- Bearded iris
- Bee balm (attracts hummingbirds)
- Goldenrod
- Feverfew
- Holly (such as Ilex x meserveae 'Blue Prince')
- Epimedium (barrenwort)
- Monarda (bee balm)
- Ramps
- Eastern redbud (new to me this year)
- New Jersey tea (new to me this year)
- Asters
- Dutchman's pipe (host plant for the pipevine swallowtail butterfly)
- Virginia creeper (this is prolific in my garden)
- Trillium
- Wild violets (host plant for fritillary butterflies)
- Virginia bluebells
- Monkshood (poisonous)
Avoid planting these near black walnuts
- Tomatoes
- Eggplant
- Potatoes
- Peppers
- Petunias
- Nicotiana
- Zinnias
- Hydrangea macrophylla
- Hydrangea paniculata
- Lilac
- Winterberry
- Rhododendron
- Peony (all)
- Rose campion
- Dahlias
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