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Gardening around Black walnut trees

March 3, 2013 By Jim 11 Comments

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An old black walnut in a hardwood forest can be a site to behold with its towering trunk.   Their wood can also make wonderful furniture.  Black walnut trees can also be majestic shade trees that bring relief in the summer heat.  If you have them in your yard and you are trying to grow a garden or landscape, they can also be a pain in the @#$!

Front yard design for Black walnut tree
Black walnut tree
photo credit: nautical2k via photopin cc

Chemical warfare

You see black walnuts (Juglans nigra) produce the chemical juglone, which is exuded from all parts of the plant. The production of juglone by the tree is used to assure its survival, by killing of other plants that try to invade its turf (bad pun alert!).

Evil face on tree
The EVIL tree that kills other trees!
photo credit: Scabeater via photopin cc

You see juglone in the soil causes problems in plants that are sensitive to it. The most common symptoms of juglone sensitivity is yellowing and wilting of leaves. This usually occurs during the hot dry periods during the growing season.  It eventually results in the death of the sensitive plant.

Is this all doom and gloom if you have a big walnut in your yard?

Well if you just want grass and your big walnut trees, it’s not a problem as turf seems unaffected.  The juglone may actually help to keep some weeds from growing.  If you want to grow other plants, then it starts to become tricky.  Especially, if any of those plants are on the following list:

Plants MOST sensitive to juglone:

ANNUALS AND VEGETABLES

Cabbage, Peppers (some), Tomatoes, Petunia’s, Eggplant, and Potato.

PERENNIALS

Colorado Columbine, Wild Columbine, Asparagus, Chrysanthemum (some), Baptisia, Hydrangea, Lilies, Daffodils, Narcissus ‘John Evelyn,’ ‘Unsurpassable’ ‘King Alfred’ and ‘Ice Follies’, Peonies, Rhubarb;

TREES

Silver Maple, European Alder, White Birches, Northern Hackberry, Apples and Crabapples, Norway spruce, Pines, Basswood;

SHRUBS

Red Chokeberry, Hydrangea, Mountain Laurels, Privet, Amur Honeysuckle, Brush Cinquefoil (Potentilla), Rhododendrons and Azaleas, Blackberry, Lilacs, Yew, Blueberry, Doublefile Viburnum;

It’s not just black walnuts (although mostly)

The greatest concentration of juglone is found in the buds, leaves, stems, nut hulls, and roots of the walnut.  The black walnut and the butternut (Juglans cinerea) are the landscape plants most recognized by gardeners as being problems.  However, English or Persian walnut (Juglans regia) and hickories (Carya) also produce juglone but to a lesser degree.

Plants okay with Walnuts

Luckily, not all plants are sensitive to juglone.  There is a lot of debate as to what plants are not bothered by it.  For instance, yew is listed as being very sensitive to it, but I know of a spot where yews have been growing very nicely for that last 12 years right next to a black walnut.  Some lists also say crabapples are fine, and some say they are sensitive to it.  My advice is to look at several lists and try to find plants that appear on several of them as being tolerant.  I have included some links to lists below.

Landscaping and Gardening around Walnuts and Other Juglone Producing Plants

Black Walnut Toxicity to Plants, Humans and Horses

How to grow Juglone sensitive plants

If you can’t live without your tomatoes or some other plant that is sensitive to walnuts.  What you need to do is keep their roots away from the walnut roots and leaves.

Option #1 – Grow your plants in pots with potting soil

Option #2 – Grow your plants in a raised bed.  This will require lining the bed to reduce root contact using weed fabric and filling the raised bed with new topsoil.  This won’t really work for trees and shrubs whose roots will want to grow deeper, but is fine for shallow rooted perennials and vegetables.

Option #3 – Cut the tree down.  It will probably take two to three years before you can start growing juglone sensitive plants though.

Landscape Design tolerant of Black Walnuts

If you are keeping the walnut and want to landscape, you will have to pick plants that are walnut tolerant.  Next post, I will help a reader who wants a front yard design, but has mature black walnuts in her parkway.  Here is a picture of her house:

Front yard design house in summer.
House in summer

Her house is in planting zone 5 in dappled shade.  Beside the walnuts, she has a large sycamore tree in her front yard.  She likes Asian influenced designs but wants to keep it low maintenance.  I will show a basic front yard design that hopefully meets her needs.

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Filed Under: Gardening Tagged With: Black walnuts, front yard design, juglone, landscaping

Comments

  1. Maureen says

    December 20, 2017 at 10:19 am

    Is there a soil additive that counteracts juglans?

    Reply
    • Jim says

      December 30, 2017 at 1:04 pm

      Not that I am aware of.

      Reply
  2. Beverly says

    October 10, 2016 at 1:56 pm

    Very nicely written and informative article. I have found the info very encouraging and helpful, as I am sure others have! Will look for this site again! Thank you and “happy gardening”! Ms Bee

    Reply
  3. Lindsay says

    September 12, 2016 at 10:55 am

    Thank you for your wonderful posts. I found them really helpful and inspiring!

    Reply
  4. Diane Schildgen says

    September 10, 2015 at 12:19 pm

    I don’t have a problem with a walnut tree, but with the squirrels that bury the nuts in my planters and beds. Is there any way to stop these critters?

    Reply
    • Jim says

      September 12, 2015 at 12:07 pm

      I have no simple answers for you other then a high powered pellet gun. Just kidding my daughters favorite animal is the squirrel, she would be horrified at that. Perhaps I’ll do a post on this, but I’ll need to research that a bit.

      Reply
  5. Ceil Carey says

    March 5, 2013 at 7:13 am

    We have black walnut trees in our yard so this is great. Thanks, Jim.

    Reply
    • Jim says

      March 6, 2013 at 6:37 pm

      Glad you found it helpful.

      Reply
  6. Jim says

    March 3, 2013 at 9:23 pm

    I had research it a bit, but chemicals in creosote bush roots and leaves do inhibit the growth of other plants (Mabry et al. 1977).

    It exhibits allelopathic activity just like juglone and inhibits the growth of other plants around it, even it’s own seedlings.

    So the answer is not Juglone, but other chemicals that do the same thing.

    Reply
    • Jeanf says

      March 4, 2013 at 2:44 pm

      Thanks Jim.

      Reply
  7. Jeanf says

    March 3, 2013 at 11:37 am

    Jim, we notice that nothing will grow under or near native (Sonoran desert) creosote bushes. Everything dies. Do creosotes secrete juglone also?

    Reply

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