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#ProPlantTips - Walnut Toxicity & Juglone Resistant Plants!

#ProPlantTips - Walnut Toxicity & Juglone Resistant Plants! - Nature Hills Nursery

Charlotte Weidner |

Ever notice that patch of bare earth beneath your Walnut trees? All trees in the Black Walnut family (Juglans), plus cousins like the Butternut and some Hickory trees, all produce a toxic substance known as juglone through their roots, carried in their leaves and stems and even seeping into the rainwater that washes over the foliage and falls to the ground!

What is it about Walnut Trees?

trunk base

Juglone is highly toxic to many plants, acting as a natural herbicide, it kills almost anything beneath their canopies ‘drip-line’ and beyond! This is a self-preservation trick to reduce competition for water and nutrients, ensuring the Walnut tree gets it all!

For the gardener, that means it also prevents many plants from growing under or near them. Occurring in the highest concentrations in the new buds, shells and hulls, and in their far-reaching roots, it’s also present in the leaves, bark, stems and twigs. Anything that comes in contact with the ground begins to decay and releases into the soil, adding to the build-up of juglone, laying waste to anything even thinking about competing for water and nutrients in the soil!

A mature Black Walnut tree that’s been present in a location for a long time can have a ring of death 50 plus feet out past the drip line! Younger trees obviously have less of an effect on their environment, but eventually, they will win in the long run.

While the shade from your Walnut tree will be lovely, it doesn’t leave much room for a garden. Even gardeners that rigorously rake up fallen leaves, clean up the fallen nuts and keep the area neat and tidy, will see anything, including turfgrass, begin to wither.

Juglone Symptoms

Plants affected by Juglone become stunted, discolored and slowly die, all showing the same symptoms of herbicide drift or other chemicals sprayed onto them, or even appearing as if a pest or disease is affecting your plants. Before you reach for the sprayer to treat it, look around to see if you have, or had, a Walnut tree nearby!

The toxicity can remain in the ground for weeks to months, sometimes years, depending on how much of the tree still remains in the ground. Those underground roots will still be decomposing and releasing more juglone.

Once affected, plants cannot be transplanted in hopes of recovery, the juglone effects are permanent.

Solutions

mulch

Unfortunately, there is no spray or treatment; only time and the systematic removal of all remaining parts of an old tree. For currently living trees, luckily there are a few workarounds you can put in place to still enjoy gardening in the shade of your mightly Walnut tree!

Cover It Up

Sometimes the easiest way to deal with juglone is to create a mulched area beneath the tree, not only does this give your tree a finished look and a clean line and a polished look, it makes for easy clean up of leaves and debris. And no worry about plants dying if there aren’t any.

Rise Above

plants in pots

Putting a barrier down under the raised bed, or very high mounded planting berm, to prevent juglone from seeping upwards. Using soil that is juglone free you can plant mildly to fully resistant plants without too much worry. Just be rigorous in cleaning up falling debris from your tree that lands in and onto the area.

Create a container garden using varying heights of pots or large planters that will be kept separate from the effects.

You’ll still need to use plants that are resistant because of the eventual saturation due to rainfall that picks up juglone on the way through your tree and into the raised planting areas.

Surface Deep

Uncovered roots

Choose shallow-rooted and resistant plants that don’t grow too deeply into the soil, adding a layer of very well-draining fresh soil (without burying the trunk of your tree, also helps resistant plants cope with the effect.

These plants will of course need a good layer of mulch that will help add a barrier from fallen debris from decaying into the soil. Again, you’ll want to religiously remove fallen matter from the planting area.

Plant Resistant Varieties

Take a look around at neighbors and in parks where you see Black Walnuts and observe what does well and what doesn’t. Nature is the first to break her own rules and you’ll start seeing what plants do well despite the juglone!

chairs under a tree

Not only are you fighting the chemical compounds in the soil, but also shade! This can be a highly limiting factor on what can grow beneath the dense canopy of your tree. At least the squirrels looking for nuts won’t be much of a problem.

Here are a few plants that are excellent choices for a juglone saturated environment and will do well despite your Walnut tree's best attempts at hogging the area for themselves!

Plants That are Resistant to Juglone

Trees

In nature, you’ll see Crabapples, Dogwoods, Silver and other types of Maples, Elm trees and Locust growing side by side with Walnuts. Hemlock and Eastern Red Cedar seem unaffected as well. Choose native forms of these plants since their cultivars aren’t as hardy and tolerant.

Understory Trees

  • White Flowering Dogwood Tree
  • Pagoda Dogwood
  • Pawpaw Trees
  • Birch Trees
  • Goldenrain Tree
  • Tulip Tree
understory trees

Shrubs

shrus

Perennials

  • Hummelo Betony (Lambs Ear)
  • Hemerocallis Daylily
  • Ironweed
  • Fireworks Evening Primrose
  • Siberian Iris and Purple Flame Iris
  • Younique Pink False Spirea (Astilbe)
  • Lenten Roses (Helleborus)
  • Most Wildflowers & Native Plants
perennials

Groundcover

  • Bulbs like Muscari
  • Lungworts
  • Ajuga
  • Lady Ferns
  • Coral Bells
  • Most Hosta Plants
  • Liriope (Lilyturf) is a great lawn replacement & perennial groundcover!
Groundcovers

Fruit

Fruit shrubs and plants that you see growing in the wild are usually the best rated for growing near Walnut trees, however for fruit to do well, they need sun, and they won’t get much under the tree's canopy.

Some native Grapevines do well, Quince and native black raspberries. Remember though, fruit needs sun to really give you the best harvest.

Can’t Beat Them? Join Them!

trees in a field

If you have the room, go ahead and plant your own nut tree grove and include Butternuts, other Black Walnut varieties and Hickory Nut Trees! Throw in a few Hazelnuts and Chestnuts for a squirrel and bird-friendly forest of snacks!

Plus more good news - after raking up after your Black Walnut, those leaves can be compost just fine and won’t leach further juglone into your garden. The composting process and air oxidize the chemical very quickly so it breaks down safely for use in your vegetable beds and beyond.

If worst comes to worst, just lay down a patch of Arborist’s bark chips and a hammock for you and a swing for the kids, and relax in the shade! You’ll have a yummy harvest of Walnuts for roasting and snacking on while you do!


Head over to NatureHills.com for everything you need to enjoy your backyard spaces!

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Frequently Asked Questions

Do all walnut trees produce juglone, or just black walnuts?
All trees in the Juglans family produce juglone, not just Black Walnuts. This includes Butternuts and certain Hickory trees as well. The concentration varies by species, with Black Walnuts being the most potent offenders, but any walnut relative in your landscape should be treated as a potential source of soil toxicity. If you have any of these trees on your property, plan your garden beds accordingly and consult our list of juglone-resistant plants before planting within 50 feet or more of the canopy drip line.

Can hydrangeas grow near black walnut trees without being harmed?
Hydrangeas are unfortunately sensitive to juglone and will struggle or fail to thrive when planted near black walnut trees. The toxic zone can extend 50 feet or more beyond the tree's drip line, so simply planting at the edge of the canopy is not enough to protect them. If you want to grow hydrangeas on a property with black walnuts, choose a planting location well outside that 50-foot radius and test the soil first, as juglone can persist for years even after a tree is removed.

Are hostas juglone tolerant enough to plant near walnut trees?
Hostas are actually one of the better choices for planting near walnut trees, as they have demonstrated a reasonable tolerance to juglone. That said, tolerance does not mean immunity, so you should plant hostas outside the immediate drip line when possible and avoid areas where heavy root concentration or nut and leaf debris accumulates. Keep the area clean of fallen walnut material, and monitor your hostas closely in the first season or two to ensure they are establishing well rather than showing signs of stress like yellowing or stunted growth.

Are roses juglone tolerant and safe to plant near walnut trees?
Roses are generally not considered juglone tolerant and are at significant risk when planted near Black Walnut trees. The toxic zone can extend 50 or more feet beyond the drip line of a mature walnut, meaning roses planted even at a considerable distance may experience stunting, discoloration, and eventual death. Because juglone damage is permanent and affected plants cannot be successfully transplanted to recover, it is best to choose a planting site for your roses that is well outside this danger zone, or select one of the known juglone-resistant plants for areas close to your walnut trees.

Are raspberries juglone tolerant or will they struggle near walnut trees?
Raspberries are notably sensitive to juglone and will struggle and likely die when planted near black walnut trees. The toxic zone can extend 50 or more feet beyond the drip line of a mature walnut, so distance alone is rarely enough to protect them. To grow raspberries successfully, site them well outside this range and avoid any areas where walnut roots, leaves, or hulls have historically decomposed in the soil, as juglone can persist for years even after a tree is removed.

Is spirea juglone tolerant and a good choice for planting near walnut trees?
Spirea is generally considered juglone tolerant, making it a solid choice for planting near Black Walnut trees. However, keep in mind that even tolerant plants can struggle if placed too close, as mature Black Walnuts can have a toxic zone extending 50 or more feet beyond their drip line. For the best results, plant spirea at the outer edges of this zone and monitor closely during the first growing season for any signs of stunting or discoloration. If you see healthy new growth after the first full year, your spirea has successfully established in the juglone-affected area.

What plants grow well under or near a black walnut tree?
Many plants have developed resistance to juglone and can thrive near black walnut trees, including Kentucky bluegrass, tall fescue, ajuga, astilbe, hostas, daylilies, and certain native wildflowers like Virginia bluebells. Vegetables such as squash, melons, beets, and corn are also generally tolerant, while tomatoes, peppers, and potatoes are highly sensitive and should be kept well beyond the drip line and its 50-plus-foot zone of influence. When planting near a black walnut, choose proven juglone-resistant varieties and avoid amending the soil with walnut leaves or hulls, which release additional toxins as they decompose. Start with a small planting trial before committing to a large garden bed in the area.

How far from a black walnut tree does juglone toxicity affect surrounding plants?
Juglone toxicity from a mature Black Walnut tree can extend 50 or more feet beyond the tree's drip line, meaning the affected zone can be surprisingly vast. Younger trees have a smaller radius of influence, but their impact grows steadily over time as roots spread and organic matter accumulates in the soil. When planning your garden, measure outward from the canopy edge and add at least 50 feet to that distance to establish a safe planting zone, and keep in mind that toxicity can persist in the soil for weeks, months, or even years after a tree is removed.

How do you prepare a garden bed near a walnut tree to protect sensitive plants?
Preparing a garden bed near a walnut tree for sensitive plants is extremely difficult because juglone permeates the soil through roots, decomposing leaves, and rainwater runoff, and can extend 50 or more feet beyond the tree's drip line. There is no spray, treatment, or soil amendment that neutralizes juglone, so the most reliable approach is to choose plants that are naturally resistant to juglone toxicity rather than attempting to protect sensitive ones. Remove fallen leaves, nuts, and debris promptly to reduce the ongoing addition of juglone to the soil, and consider raised beds with a physical barrier, though root intrusion can still be a long-term concern. Your best course of action is to research and plant juglone-tolerant species suited to your growing zone, as these are your strongest guarantee of gardening success near walnut trees.

Should you remove black walnut leaves and debris to reduce juglone buildup in the soil?
Yes, you should absolutely remove black walnut leaves, fallen nuts, hulls, and twigs as promptly as possible, since any organic material from the tree that contacts the soil will decompose and release additional juglone. However, understand that cleanup alone will not solve the problem, because the roots extending 50 or more feet beyond the drip line are the primary source of juglone and cannot be managed through raking. Do not compost any walnut debris, as the juglone will persist in the compost and contaminate wherever you spread it. Focus your cleanup efforts on consistent removal of all surface debris throughout the growing season, and dispose of it in the trash or through municipal yard waste programs.
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