Gardening Under Black Walnuts

Gardening under black walnut trees can present a unique set of challenges due to the release of juglone, a chemical compound found in the tree’s roots, leaves, and nuts. However, with some healthy garden habits and some careful plant selection, you can create a thriving garden beneath these majestic trees!

Effects of Juglone

Juglone sensitive plants within the root zone or drip zone are most at risk for symptoms of toxicity including wilting, yellow leaves, stunted growth or plant death. If you happen to catch it early, you can try digging up the plant, gently rinsing off the roots of all soil in a bowl or bucket, and potting into a new juglone free location (juglone can sometimes damage or kill a plant quickly, but this sometimes works!).

How to Reduce Juglone Side Effects

When it comes to the care of your garden, some studies have shown that healthier soil with lots of active microorganisms can help protect plants a little more by breaking down juglone faster. Our tips to reduce the impact of juglone in your gardens: 

• remember to remove leaves, sticks, branches and dropped walnuts as much as possible from your gardens
• add a healthy layer of compost (that doesn’t include black walnut leaves or husks) in the spring and fall 
• make sure soil has good drainage
• avoid chemical fertilizers when possible to encourage more biodiversity in your soils
• take advantage of raised beds and/or containers when possible

Juglone Tolerant Plants for your Ontario Gardens

There are never any guarantees as each garden is different and will have success with different plants, but the following plants are more commonly noted as juglone tolerant options! Keep in mind that there is no ‘finished’ list for juglone tolerant plants that will work in your garden, and there may be many options not listed here that will grow for you. Getting a thriving garden with black walnuts in the area is always a bit of a trial and error process!

Juglone Tolerant Perennials

Part Shade to Full Shade

• Astilbe (Astilbe spp.): Known for its feathery plumes of flowers in various colours, Astilbe thrives in moist, well-drained soil.
• Hosta (Hosta spp.): Renowned for their elegant foliage, Hostas are excellent shade-loving perennials available in a wide range of sizes and leaf colours.
• Bleeding Heart (Dicentra spp.): With heart-shaped flowers dangling from arching stems, Bleeding Hearts bring charm to shady spots.
• Coral Bells (Heuchera spp.): Offering a colourful array of foliage, Coral Bells add texture and interest to the garden.
• Foamflower* (Tiarella spp.): This delicate perennial produces clusters of tiny flowers above foliage resembling foam, ideal for shady locations.
• Japanese Forest Grass (Hakonechloa spp.): Graceful and low-growing, this grass-like perennial adds a touch of elegance to any shade garden.
• Lungwort (Pulmonaria spp.): Known for its attractive foliage and clusters of colourful flowers, Lungwort is a tough perennial for shade.
• Solomon’s Seal* (Polygonatum spp.): Featuring arching stems and dangling white flowers, Solomon’s Seal brings a graceful presence to woodland gardens.
• Virginia Bluebells* (Mertensia virginica): These bell-shaped, blue flowers emerge in early spring, creating a beautiful carpet of colour.
• Japanese Anemone (Anemone × hybrida): This elegant perennial produces beautiful, nodding flowers in shades of white and pink and can withstand juglone.
• Ostrich Fern* (Matteuccia struthiopteris): This elegant fern thrives in moist, shady conditions and can withstand juglone toxicity.
• Woodland Phlox (Phlox divaricata): Fragrant and charming, Woodland Phlox forms a carpet of lavender-blue flowers in spring.
• Siberian Iris (Iris sibirica): With its stunning flowers and slender foliage, Siberian Iris thrives in moist soil and can handle juglone exposure.
• Virginia Sweetspire (Itea virginica): A versatile shrub-like perennial, Virginia Sweetspire offers attractive foliage, fragrant flowers, and juglone tolerance.
• Creeping Phlox (Phlox subulata): This low-growing perennial forms a dense carpet of colourful flowers and is well-adapted to juglone-exposed areas.
• Cardinal Flower* (Lobelia cardinalis): With its vibrant red flowers and preference for moist soil, Cardinal Flower is a striking choice for juglone-tolerant perennials.
• Hellebore (Helleborus spp.): Hellebores offer early-season blooms in shades of white, pink, and purple, and they are known for their tolerance to juglone.

Part Sun or Full Sun

• Coneflower* (Echinacea spp.): Coneflowers are popular perennials known for their showy, daisy-like flowers in shades of pink, purple, and white. They are resilient, drought-tolerant, and can thrive in part sun to full sun conditions.
• Black-Eyed Susan* (Rudbeckia spp.): Black-Eyed Susans are cheerful, yellow flowers with dark centers that bloom from summer to fall. They are tolerant of juglone and prefer full sun to part sun.
• Bee Balm* (Monarda spp.): Bee Balm produces vibrant, nectar-rich flowers that attract pollinators to the garden. They come in various colours and can tolerate juglone in part sun to full sun conditions.
• Daylily (Hemerocallis spp.): Daylilies are reliable perennials that come in a wide range of colours and sizes. They have a high tolerance for juglone and can thrive in part sun to full sun areas.
• Sedum (Sedum spp.): Sedums are succulent perennials that offer fleshy foliage and clusters of flowers in shades of pink, red, and white. They are drought-tolerant and can handle juglone in part sun to full sun locations.
• Russian Sage (Perovskia atriplicifolia): Russian Sage is a woody perennial with aromatic silvery-gray foliage and tall spikes of lavender-blue flowers. It prefers full sun to part sun and can tolerate juglone.
• Catmint (Nepeta spp.): Catmint is a low-maintenance perennial that produces spikes of lavender-blue flowers. It is drought-tolerant, attracts pollinators, and can handle juglone in part sun to full sun conditions.
• Lamb’s Ear (Stachys byzantina): Lamb’s Ear is a unique perennial with fuzzy, silver-gray leaves that resemble lamb’s ears. It prefers full sun to part sun and can tolerate juglone exposure.
• Coreopsis* (Coreopsis spp.): Coreopsis are daisy-like flowers with bright yellow or pink petals that bloom throughout the summer. They are hardy, drought-tolerant, and can handle juglone in part sun to full sun areas.
• Feather Reed Grass (Calamagrostis x acutiflora): Feather Reed Grass is an upright grass with narrow, feathery flower spikes that emerge in early summer and persist into winter.
• Little Bluestem* (Schizachyrium scoparium): Little Bluestem is a native prairie grass with blue-green foliage that turns reddish-bronze in the fall. It is adaptable to various soil conditions, including juglone-affected areas, and prefers full sun.
• Switchgrass (Panicum virgatum): Switchgrass is a versatile grass known for its upright form and attractive seed heads.
• *Ontario native varieties included

Juglone Tolerant Ontario Native Plants

Part Shade or Full Shade

• Wild Columbine (Aquilegia canadensis): A native wildflower with unique red and yellow flowers that attract hummingbirds.
• Wild Geranium (Geranium maculatum): Featuring attractive foliage and delicate pink or purple flowers, Wild Geranium is a native woodland plant.
• Joe-Pye Weed (Eutrochium spp.): Tolerant of shade and wet conditions, Joe-Pye Weed produces clusters of pink or purple flowers that attract pollinators.
• Wild Ginger (Asarum canadense): This low-growing woodland plant has heart-shaped leaves and unique, bell-shaped flowers, adding a touch of charm to shady areas.
• Canada Anemone (Anemone canadensis): This delicate, white-flowered perennial thrives in moist, shady conditions and brings elegance to woodland gardens.

Part Sun or Full Sun

• Butterfly Weed (Asclepias tuberosa): This vibrant orange-flowered perennial is a host plant for monarch butterflies.
• Purple Coneflower (Echinacea purpurea): A classic native plant with showy pink-purple flowers that provide nectar for bees and butterflies.
• Wild Lupine (Lupinus perennis): With its tall spikes of blue flowers, Wild Lupine is not only a beautiful addition but also an important plant for supporting native wildlife.
• Wild Bergamot (Monarda fistulosa): Also known as Bee Balm, Wild Bergamot features aromatic foliage and clusters of pink to lavender flowers, attracting pollinators to your garden.
• New England Aster (Symphyotrichum novae-angliae): This vibrant native aster produces clusters of purple, pink, or white flowers, attracting butterflies and bees to your garden.

Juglone Tolerant Annuals

Part Shade or Full Shade

• Impatiens (Impatiens spp.): Offering a variety of colourful blooms, Impatiens are popular annuals that thrive in shady areas.
• Begonia (Begonia spp.): With their attractive foliage and vibrant flowers, Begonias are well-suited for part shade gardens.
• Torenia (Torenia spp.): Also known as “Wishbone Flower,” Torenia blooms in shades of blue, pink, and purple, adding charm to shaded spots.
• Lobelia (Lobelia spp.): These delicate annuals produce profusions of blue, white, or pink flowers, bringing a pop of colour to shade gardens.
• Caladium (Caladium spp.): Known for their beautiful and colourful leaves, Caladiums thrive in shady, moist conditions.

Part Sun or Full Sun

• Marigold (Tagetes spp.): Marigolds are vibrant annuals that come in a variety of colours. They are known for their tolerance to juglone and their ability to attract beneficial insects to the garden.
• Zinnia (Zinnia spp.): Zinnias are popular annual flowers that produce bright and colourful blooms. They thrive in sunny locations and can tolerate juglone exposure.
• Portulaca (Portulaca grandiflora): Portulacas, also known as moss roses, are low-growing annuals with succulent-like foliage and vibrant, showy flowers. They are drought-tolerant and can tolerate juglone.
• Cosmos (Cosmos spp.): Cosmos are airy, daisy-like flowers that add a delicate touch to the garden. They are easy to grow, prefer full sun, and have some tolerance to juglone.
• Salvia (Salvia spp.): Salvias are versatile annuals that come in a wide range of colours and sizes. They attract pollinators and can thrive in part sun to full sun, making them suitable for juglone-affected areas.

Juglone Tolerant Understory Trees:

• Serviceberry (Amelanchier spp.): A small tree with beautiful white flowers and edible berries, Serviceberry thrives in part shade.
• Redbud (Cercis spp.): This flowering tree produces vibrant pink or purple blooms before its leaves appear, adding early-season interest.
• Flowering Dogwood (Cornus spp.): With its eye-catching flowers and colourful berries, Dogwood trees are an excellent choice for shade gardens.

Juglone Tolerant Vegetables:

• Lettuce (Lactuca sativa): Leafy greens like lettuce are well-suited for part shade and can be harvested for fresh salads.
• Swiss Chard (Beta vulgaris var. cicla): This nutritious leafy green tolerates part shade and can add colour to your vegetable garden.
• Radishes (Raphanus sativus): Quick-growing and hardy, radishes can tolerate partial shade and are a great addition to salads.
• Spinach (Spinacia oleracea): Spinach is a cool-season vegetable that thrives in part shade to full sun. It is known for its nutrient-rich leaves.
• Snap Beans (Phaseolus vulgaris): Snap beans, both bush and pole varieties, are resilient vegetables that thrive in full sun and produce delicious, tender pods.
• Beets (Beta vulgaris): Beets are hardy and versatile vegetables that come in a range of vibrant colours and offer both tasty roots and nutritious greens.
• Onions (Allium cepa): Onions are reliable and resilient vegetables that come in various shapes and sizes, from pearl onions to green onions to large cooking onions.
• Garlic (Allium sativum): Forms distinctive bulbs composed of individual cloves and adds a wonderful taste to various cuisines.

Overall the scientific information on juglone and specific plants is pretty limited, and most lists can be anecdotal in nature, so roll up those sleeves and get those hands dirty (and good luck!).