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How long does black walnut toxin persist in the soil?

Posted by Paula_sfbay 9-sunset 17 (My Page) on
Fri, Mar 21, 03 at 19:39

Any one have any idea how long the black walnut toxin lasts? I have three walnut trees in my back yard, grafted onto what I think
are black walnut bases. The trees on the top have died. The bases are sending up suckers. I'm thinking of trimming off the suckers.
In a couple of years, the trees should die off completely. Then I'll have three beautiful structures to support gorgeous, huge, rambling roses, ones I'm afraid to grow on the fence for fear they'll be too heavy. This will only work if the toxin fades away when the tree
finally dies. So, back to my original question. Does the toxin persist in the soil after it is no longer being produced, or does it break
down over time? And if so, how long does it take?


Follow-Up Postings:

RE: How long does black walnut toxin persist in the soil?

Paula, I have read one year and five years. I would trust the five year to completely get rid of the toxin. The roots take a long time to die and will contain the poisen until they are completely dead.
Good luck!

RE: How long does black walnut toxin persist in the soil?

On the other hand, you will be adding soil to plant your roses in... and the roots won't be in that soil, will it?

I'd say go for it, but don't put your most precious rose there the first year.

I say this, having many things growing under a black walnut and English walnut. There are even roses just outside the canopy of each of them.

RE: How long does black walnut toxin persist in the soil?

Okanagan, What else have you had good luck with growing near a BW?

RE: How long does black walnut toxin persist in the soil?

You may wish to check the link below. Walnut roots extend well beyond the drip line and may affect plants at a distance equal to the height of the tree

This season we will be relocating many of our plants due to a Black Walnut on the neighbors property that is hindering our plants growth.

Here is a link that might be useful: Black Walnuts (Junglans nigra) Causing Wilt

RE: How long does black walnut toxin persist in the soil?

  • Posted by Susy Zone 5/6 MO. (My Page) on
    Sun, May 4, 03 at 20:13

Here is what grows successfully for me under and around a walnut tree---have lots of them in my yard. Some of these plants listed are under and around an old apple tree that is near and under the walnut tree. (Make sense? :>)

Hemerocallis (Daylily)
Pulmonaria (Lungwort)
Heuchera (Coral Bell)
Oakleaf Hydrangea
Polemonium (Jacob's Ladder)
Imperata (Japanese Blood Grass)
Tiarella (Foam Flower)
Dicentra (Bleeding Heart)
Ajuga (Bugleweed)
Lamium (Dead Nettle)
Aegopodium (Bishop's Weed)
Tricyrtis (Toad-Lily)
Tovara (Painter's Palette)
Mertensia (Virginia Bluebells)


RE: How long does black walnut toxin persist in the soil?

Thanks so much for posting your list! Its so helpful to see what others have had successes with... I'm particularly excited to see that oakleaf hydrangea do ok near a BW...


RE: How long does black walnut toxin persist in the soil?

I bought my house 11 years ago because I loved the walnut trees in the back. I also love gardening.
Walnut trees produce a type of toxin that is not compatible with most garden vegetables.
This is what I did and I have had great results.
1. Tilled up the soil
2. Put down a (organic) barrier such as newspaper, could use black gardeners cloth.
3. Put down a layer of charcoal. My thinking was that if it can absorb toxins in the body it could also absorb them from the soil. (DO NOT USE CHARCOAL THAT HAS CHEMICAL ADDITIVES such as "self ignite")
4. Add landscaping timbers or anything else to make a raised bed. Mine has 3 levels that look like long horizontal steps. The low bed the medium bed and the high bed.
5. I got lots of aged sheep manure (few weed seeds)and put that down.
6. Added peat moss and good black dirt.
7. More aged sheep manure (few weed seeds)and put that down.
8. More peat moss and good black dirt.
9. More aged sheep manure.
10 Tilled the soil
11. Added sand to areas that I would rotate crops needing more sand.
12. Put a rubber maid trash can that I drilled a hole into the bottom. Then inserted a water control device that can be turned on and off at the bottom. Just drill a hole using the correct size drill bit and put a good silicon caulk around the water control device. Cut a hole in the top of the trash can lid for the rain spout to drain into the trash bucket.(Need a tight seal to prevent insects from breeding) Now you have your modern day rain barrel
Using a 3 way adapter I was able to attach 3 soaker hoses and use the water run off from the roof when there is no rain.
In the fall I cover the garden with old tarps, table cloths etc. to prevent any toxic droppings from the trees to enter my garden. (walnuts, leafs etc)Dark colored plastic or tarps also help warm the soil in the spring.
I do not know if there is any correlation but I also use organic, crop rotation, companion planting and plant by the moon signs or Farmers Almanac.

Add a little TLC and LOVE and you will have a great garden!

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