What to Plant Under or Near Black Walnut Trees (Without Losing Your Mind)

If you’ve got a black walnut tree in your yard here in Georgina’s Zone 5, congratulations—you’re dealing with one of the most beautiful and most complicated trees in the gardening world. Black walnuts (Juglans nigra) are native, majestic, and valuable for wildlife and wood… but they can also be a real pain in the garden. So, what’s the big deal? Let’s dig in—literally and figuratively.

 

What Are Black Walnut Trees?

Black walnut trees are large, deciduous hardwoods that can grow up to 30 metres tall with a wide canopy and thick trunk. Native to eastern North America, these trees are prized for their rich, dark wood and edible nuts (if you can beat the squirrels to them).

They’re tough, drought-resistant, and long-lived—perfect if you're into legacy trees. But if you're a gardener, you’ve probably noticed one key detail: not everything wants to grow near them.

Why Are Black Walnut Trees So Tricky?

The problem? A little chemical called juglone.

Black walnut trees produce juglone, a natural compound that’s toxic to many other plants. It’s found in the roots, leaves, bark, and even the nut hulls. Juglone inhibits growth and can outright kill sensitive plants that are too close.

Even after a black walnut tree is cut down, juglone can remain in the soil for several years, especially if roots and debris are left behind. It’s nature’s version of “don’t plant here.”

 

Symptoms of Juglone Toxicity in Plants

If you’ve planted something under or near a black walnut and it mysteriously wilts, yellows, or just up and dies for no apparent reason—it’s probably juglone toxicity.

Some common signs include:

• Yellowing or wilting leaves
• Stunted growth
• Poor production of fruit or flowers
• Sudden collapse in midsummer

 

What Can You Plant Near or Under Black Walnut Trees?

Good news: not all plants are drama queens. Some can happily live with black walnut trees and ignore juglone like it’s yesterday’s news.

Juglone-Tolerant Trees

• Serviceberry (Amelanchier spp.)
• Eastern red cedar (Juniperus virginiana)
• Hawthorn (Crataegus spp.)
• Hackberry (Celtis occidentalis)
• Honeylocust (Gleditsia triacanthos)
• Ironwood (Ostrya virginiana) 

Juglone-Tolerant Shrubs

• Forsythia
• Spirea
• Viburnum dentatum (Arrowwood)
• Potentilla
• Sumac (like Low Grow or Staghorn)
• Rugosa Roses
• Elderberry (Sambucus canadensis) 

Juglone-Tolerant Perennials

• Hostas
• Lungwort (Pulmonaria)
• Bee Balm (Monarda)
• Ferns (like Ostrich or Christmas fern)
• Astilbe
• Daylilies (Hemerocallis)
• Virginia bluebells (Mertensia virginica)
• Lily of the Valley (Convallaria majalis)
• Black-eyed Susan (Rudbeckia)
• Yarrow (Achillea)
• Solomon’s Seal (Polygonatum) 

Juglone-Tolerant Annuals

• Impatiens (some varieties)
• Zinnias
• Marigolds (Tagetes)
• Cleome
• Snapdragons
• Sweet alyssum 

Pro Tip:

While annuals aren’t as long-term an investment, they’re a great way to test a space to see how tolerant it is—especially if you're not sure how far the root system of your black walnut spreads.

Tips and Tricks for Gardening Near Black Walnut Trees

Know the Root Zone

The majority of the juglone is concentrated in the root zone, which can extend as far as the tree is tall. Keep sensitive plants outside that radius if possible. 

Raise It Up

Create raised beds with landscape fabric underneath to help reduce root intrusion. This can give you a juglone-free planting zone right near the tree. 

Clean Up Debris

Rake up fallen leaves, twigs, and nuts regularly—juglone can leach into the soil from decaying plant matter. 

Improve Drainage

Well-drained soils reduce the effects of juglone because the chemical leaches away more easily in moist, well-aerated conditions. 

Add Organic Matter

Compost, mulch, and other organic matter can dilute the concentration of juglone and improve your soil’s ability to support life. 

Don’t Compost Walnut Debris

If you're making your own compost, avoid adding black walnut leaves, nuts, or twigs—it will contaminate the whole pile with juglone. 

Try Containers

If you want to grow juglone-sensitive plants (like tomatoes or hydrangeas), try large decorative pots or grow bags out of root range.

 

Sensitive Plants to Avoid Near Black Walnuts

Skip planting these near or under black walnuts—they’re juglone crybabies:

• Tomatoes, potatoes, peppers, eggplant (a.k.a. the entire nightshade family)
• Blueberries
• Asparagus
• Peonies
• Hydrangeas
• Lilacs
• Rhododendrons and azaleas
• Birch trees
• Apple trees

 

Final Thoughts: Don’t Let Black Walnut Trees Intimidate You

So there you have it, yes, black walnut trees can be finicky neighbours—but they’re not impossible. With the right plant choices and a few tricks up your sleeve, you can absolutely have a thriving garden beneath their canopy. Embrace the challenge! After all, gardening is part science, part art, and a whole lot of experimenting. And when you get it right? It’s pure magic. Come visit us at Georgina Garden Centre. Our staff knows the quirks of Zone 5 gardens—and we’re not afraid of a little juglone.

Bonus Tip: Wildlife Love 'Em

Don’t forget—black walnut trees provide food and shelter for squirrels, birds, and other wildlife. Even if it makes planting trickier, they’re ecological powerhouses worth working with, not against.

Happy gardening!