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Black Walnut question as a mulch

Posted by juliany 5/6 (My Page) on
Wed, Sep 16, 09 at 14:21

After posting on another forum and learning of the potential issues that Black Walnut can pose to plants, I'm trying to determine just how long I should wait before applying mulch from a Black Walnut tree to my flower garden? We have a TroyBilt chipper/mulcher machine which finely chips/mulches branches.
The branches have been in a brush pile for well over a year.

Thanks for any advice/feedback you can provide.


Follow-Up Postings:

RE: Black Walnut question as a mulch

What are you putting them on? Juglone breaks down pretty well in a year. I wouldn't put it on tomatoes or other highly sensative plants, but many things would be fine.


RE: Black Walnut question as a mulch

I am using the chips/mulch on my perennial beds.

Juglone is not toxic after a year?


RE: Black Walnut question as a mulch

i would use it..

how can a 2 or 3 inch layer of chipped wood have enough juglone.. to have any impact???

go thinner if you are worried ....

many.. many things grow under walnuts .... IF THERE IS ENOUGH LIGHT .... as noted.. some things MIGHT not be tolerant.. but i bet you might be surprised how few things ....

the effect of a thin layer.. is NOT going to be the same as trying to grow something under a 50 year old mature tree ....

in the alternative.. pile it up.. and leave it until next fall.. then spread it ...

i will leave the research to you... i have no actual experience with what i am suggesting.. other than former neighbors who grew a whole shade perennial garden under black walnuts ...

good luck


RE: Black Walnut question as a mulch

Thanks for the advice. Since I grow alot of daylilies and iris I'd was hoping to first be sure it wouldn't be toxic to the plants before applying it.

I'll keep searching to see if I can find out anything more.


RE: Black Walnut question as a mulch

To add to your comfort level, juglone is in the least quantities in the woody parts of the plant.

I'd agree that after a bit of time, the allelopathy issue is moot.

RE: Black Walnut question as a mulch

  • Posted by artdeco 5 - Chicago burbs (My Page) on
    Fri, Sep 18, 09 at 0:29

Iris & Daylily is tolerent of juglone anyways, so you shouldn't have a problem.
But if you do have any special or favorite plants you hope to include, I'd research those before taking a chance. Especially if you've invested any money in this bed - it's not worth the money you save on cheap mulch.
The juglone issue varies from property to property, depending on the type of dirt you have & drainage, etc. I read that juglone breaks down much slower in shade than in sun... and it's a worm repellent...
I'm just really cursing Walnut trees this week. I just dug-out Yew #4 from a row of 5, planted a good distance from all my neighbors walnut trees. Noticed it turning yellow 3 weeks ago for no apparent reason, & it declined very quickly. Found 1 walnut buried deeply at the base by a squirrel.

RE: Black Walnut question as a mulch

juliany- I didn't say it wasn't toxic after a year, I said it breaks down pretty well after a year. It will still retain a low level of the juglone, hence my caveat in regard to tomatoes (they are arguably the most sensative plant of which I am aware). Your perennial beds should be fine.

artdeco- That walnut may be circumstantial, especially a single walnut. I have a Taxus baccata growing under the canopy of a neighbor's Black Walnut with no ill effects. My neighbor had a Taxus xmedia growing under the same Black Walnut- for over forty years. I know yews show up on some lists as sensative but I have not seen that as the case.


RE: Black Walnut question as a mulch

  • Posted by artdeco 5 - Chicago NWburbs (My Page) on
    Sat, Sep 19, 09 at 0:43

Yes, I agree it could be circumstantial; but they grew great for 3 years, the drainage was perfect, made lots of berries this summer, & it's sisters look very healthy. It's got to be the walnut.
Our neighborhd was a native walnut grove & and is very wet. Plants here are much more sensitive than at our old house. My neighbors have suggested if maybe these trees contain higher levels of juglone because the dirt is basically walnut compost & clay, so the toxin doesn't drain away. The roots emit it, then re-absorb it...?
At our old house, yews also grew at the base of BW trees, but that part of town has a sandbar below it.
Each propety is different - juglone breaks down very slowly in some places.
And I'm not really cursing walnut trees - I was just frustrated. These trees were here long before I was & contribute alot more to the environment than I do...

RE: Black Walnut question as a mulch

I learned the hard way to show a lot of respect, or perhaps to use a lot of caution, with black walnut. I composted the leaves and nut husks one time many years ago, mixed with a great deal of other leaves (ash, oak, maple, and black cherry mostly), grass clippings, and other plant matter. After a couple years of decomposition, the black, fluffy, crumbly compost looked terrific. And, it severely stunted a lot of things in my 110 x 100 foot vegetable garden for a couple of years.

Now, the walnut leaves and husks are used as mulch UNDER THE WALNUT TREES.

Now, what I can grow near or under them successfully includes pretty much anything in the compositae family -- Rudbeckia, Echinacea, Aster, Helianthus, Heliopsis, and so forth - Daylilies are OK, Iris is OK, Lilies, Lily-of-the-Valley. Astilbe and Hosta seem OK (not sure about Hosta, deer at it too fast to really tell). Sedum is OK near them. Acorus is very happy under there. Lamium, Lamiastrum, Ajuga, and English Ivy are fine, too. Yucca does OK, but its a tad shady so it doesn't bloom well. Most spring bulbs have done fine, too -- daffs, hyacinths, hyacinthoides, cammas, and tulips all do fine.

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