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Black Walnut question as a mulch

14 years ago

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.

Julia

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Comments (9)

tsugajunkie z5 SE WI ♱
14 years ago
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.

tj
Julia WV (6b)
Original Author
14 years ago
I am using the chips/mulch on my perennial beds.

Juglone is not toxic after a year?

Julia
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jon-you frame your comments in quotations, but don't specify who or what you are quoting. From what Steve and I have pointed out bw compost certainly is not benign to all plants, and can be rendered benign through appropriate composting practices. What is the point you are making? Sandy-many lists I have found show daffodils as tolerant, and I have also grown them successfully under bw. I plead ignorance in knowing the difference between daffodils and narcissus. I have also found lists that show that melons and squash can be grown under bw and that the fruits are not toxic to humans or animals. It seems the toxic juglone is not stored in the fruit or plant matter other than the bw debris itself. I will say that even the slightest trace of juglone spells death to tomatoes and peppers. I have grown Canna under bw. Most of the toxicisity of juglone, in the reports I have found comes from the roots and extend outward 1-1/2 times the height of the tree. So a 60 foot high bw intoxifies the soil in a 90 foot diamater circle from the trunk - roughly. This results in an area where many shade intolerant plants can exist.. That is why I made the comment that 'fringe' areas of a hosta bed under a bw can be useful for companion plants. My daylillies have done wonderful under bw, and the trees, in my humble opinion, are almost perfect 'dappled-shade' because of the lacy texture of the leafy fronds. The area under a bw is definitely NOT deep shade. Even the gentlest breeze allows direct sun to penetrate but not dominate. I have only gardened under bw, not intentionally used bw waste for mulch or compost. As Ken has pointed out, and the sources I have found support, leaching of juglone from surface debris doesn't penetrate far into the soil, but far enough to be toxic to seedlings of shallow rooted weeds and the plants themselves with shallow root systems such as tomatoes and peppers. The deep toxicity in soil comes from the bw root system. So to me, I don't have a fear of the thought of using surface applied bw debris as mulch or in composted applications for juglone tolerant plants. Theresa
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ken_adrian Adrian MI cold Z5
14 years ago
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

ken
Julia WV (6b)
Original Author
14 years ago
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.

Julia
rhizo_1 (North AL) zone 7
14 years ago
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.
artdeco
14 years ago
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.
tsugajunkie z5 SE WI ♱
14 years ago
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.

tj
artdeco
14 years ago
Tsugajunkie,
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...
denninmi
14 years ago
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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