Advice about planting depth & juglone toxicity from walnuts

harlgr8dane(5b ON)April 17, 2010

Hello there. We are in the process of building raised beds for a square foot vegetable garden. I have read through my books and also many posts here and it seems 8-12 inches is the suggested depth.

My questions are:

- if I use landscape fabric to line the beds will that help with juglone toxicity from the HUGE walnut trees that are relatively close by

- if not what other suggestions do you have and what should I go for drainage?


Thank you for reporting this comment. Undo
digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Well the ideal solution would be to find a location further away from the walnut trees or remove the trees - stump, roots, and all. They are going to cause you life-long problems that could be quite discouraging.

But if that can't be done then at least get as far away from them as physically possible. At the very least you have to be well out from under the the foliage drip line.

Then the best way to minimize the juglone effects is to make your raised beds deeper - 18-24" or even more if possible. The deeper the better. It won't eliminate the problems completely, just as using landscape fabric wouldn't, but it will reduce the effects substantially.

IMO using the landscape fabric would be a waste of time and money (plus impossible to replace) as it creates a pond under the bed. That pond will gradually become an juglone reservoir. Put down several layers of cardboard instead. It will eventually decompose true but in the meantime you won't have drainage problems.

Good luck.


    Bookmark   April 17, 2010 at 2:56PM
Thank you for reporting this comment. Undo
susan2010(6 Massachusetts)

Maybe something like a really "raised bed" by raising it off the ground entirely> Something like this, either purchased or made (see link).

Here is a link that might be useful: Table gardens

    Bookmark   April 17, 2010 at 4:26PM
Thank you for reporting this comment. Undo

I have to agree with the raised bed, completely off the ground. You might try buying or building your own earth boxes.

We had two giant walnut trees that were planted way too close to the house by the previous owners. (One actually smashed into our gutter every time there was strong wind.) For obvious reasons the trees had to go. The previous owners were big on gardening. They installed ten raised garden beds done in a step format. The garden beds border the house. There was also a walnut tree right next to the set of raised garden beds. Despite raising up the beds by bringing in outside soil, they were able to grow absolutely nothing!

When my husband and I had the trees removed, and the stumps grounded down, I waited three years before I tried planting in the garden beds. My first year of gardening I planted lettuce right next to the grounded down stump and carrots and cucumbers as far from the stump as possible. If the plants were going to fail, I didn't want to waste too much of my time. To my excitement and relief, everything grew great.

It is now my third year of gardening and I have successfully grown many different types of vegetables - edamame, peas, beans, peppers, kohlrabi, spinach, etc.

Walnut trees and gardening just don't mix in my opinion. If I were you, I'd strongly consider a container garden or earth boxes.

    Bookmark   April 17, 2010 at 5:36PM
Thank you for reporting this comment. Undo
gardningscomplicated(southeast michigan - 5b or 6?)

I had a nice sized walnut tree where I used to live, and my neighbor was able to grow some tomatoes next to his garage. So I looked at google maps, and the best I can tell is the tree is about 100 feet from where I remember his tomatoes being. But there's a gravel driveway between the tree and the tomato plants, and I'm not sure if that would slow down any tree root growth. And I also don't know if he just got lucky that year. I agree about the landscape fabric. I think tomato roots would eventually find a way through it. But you could still get lucky some years, depending on how far from the tree you planted stuff. I would think cutting down the tree would be a lot of work, and you'd still have to wait a long time before you were safe. I have no idea what your situation is like. But if it were me, I'd put my effort into another solution. Like the suggestions for completely raised, or really really deep beds. You could build a deep base out of straw bales pretty cheap. And there's supposed to be a lot of advantages to raised beds, like soil warming earlier in the spring. Or you could plant in containers. I added a link to a video from Love Apple Farm, where they have lots of tomatoes planted in containers.

Here is a link that might be useful: tomatoes in containers at Love Apple Farm

    Bookmark   April 17, 2010 at 9:09PM
Thank you for reporting this comment. Undo


Only BLACK WALNUT tree has the substance, juglone, that some vegetations
cannot thrive under it.The troxin exist/released from roots, bark and leaves.
Persian/English walnut does not have that toxin.
But in general , gardening under the canopy of any tree is not the best option.

    Bookmark   April 17, 2010 at 9:16PM
Thank you for reporting this comment. Undo
rhizo_1 (North AL) zone 7

cyrus, you are incorrect about that, sorry to say. All of the plants within that family (Juglandaceae) contain the allelotoxin juglone, though in lesser amounts than the Black Walnut. I believe that the English Walnut is pretty high on the list, however, with the pecans being fairly low (but still problematic).

Planting under the canopy is a definite no-no for the reasons you've listed, but the roots can extend way beyond the canopy. Root exudates can cause serious problems for juglone sensitive plants.

    Bookmark   April 17, 2010 at 11:08PM
Thank you for reporting this comment. Undo

As Cyrus says. Now black walnut and english walnut are easily distinguishable. Google for images of their leaves. English has a leaf similar to hickory, smooth edge
with the peculiar shape that becomes slightly wider getting farther from the stem, whereas black has a leaf which is much smaller, serrated, and somewhat similar to very large hornbeam leaves.

Hickory and english walnut both produce minimal amounts of juglone. One can grow anything nearby. Black produces copious amounts of the stuff, but even with a BW around you can grow a successful, if limited, garden. Greens: beet and chard. Roots: onion, garlic, beets, carrots, and parsnips. Fruits: all cucurbitae. Beans: beans and favas. These, plus most herbs, make it near a BW. It is not a bad selection, if you ask me.

I have lost ostrich ferns and thyme planted near a BW, as well as a couple of ornamental shrubs (firebush, I think, and rhododendron). I have never dared try any of the sensitive vegetables (the most sensitive are reputed to be the solanaceae), although I had a volunteer tomato from compost last year, growing 30 ft from a 70 ft BW, and it grew fine, without the minimal sign of stress.

Composted BW leaves, mixed in small amounts with other nontoxic leaves (oak and hickory), do not appear to cause harm. BW nuts are the best nut there is, but they are a real nuisance to crack and eat. Finally, IMHO plants die only when really on top of a BW root. one foot away and the plant may live.

    Bookmark   April 17, 2010 at 11:24PM
Thank you for reporting this comment. Undo
gardningscomplicated(southeast michigan - 5b or 6?)

glib - That's nice to know about being able to mix a few black walnut leaves with other leaves. I have a lot of leaves I could use as mulch, but I'm always paranoid there'll be black walnut mixed in. Do you know this from personal experience? Or did you read it somewhere? If you read it, can you post a reference to it? Everything I've read says what to avoid, but I don't remember anything that told me how much juglone is dangerous, and how much is probably not going to cause trouble. I have a hickory tree right next to one of my gardens, and haven't had any trouble with that. I didn't expect to, but I wasn't aware it produced juglone.

    Bookmark   April 18, 2010 at 2:03AM
Thank you for reporting this comment. Undo

Well of course trees in juglanoceas(?) family have similar characteristics.
But the amount of the toxin in BW is intensive.
Even despite of that there are lots of vegetations that will thrive in the presence of juglone.
Strangly, BW's own seedlings will not make it.
My experiece relates to tomatoes under BW tree, that will not survive and die by wilting.
All the literature I have read about the subject, have mentioned BW.
One study that I remember has been done by the university of Illinois.
They have actually catagorized things that will and those that won't thrive under BW.

    Bookmark   April 18, 2010 at 4:15AM
Thank you for reporting this comment. Undo
harlgr8dane(5b ON)

Thanks for the replies.

They are definitely black walnuts, not english. We would not take the trees down. There are three HUGE ones on the front of the property. I read previously that even if taken down that the remaining roots are still toxic regardless...

The completely raised beds would have been a good idea, but construction is already started on the beds, I will try to post a picture.

The garden is in the sunniest spot which is also close to water access.

Any thoughts about going 4inches down and then laying a bit of rock for drainage and i guess kind of a barrier layer and then adding soil?

Maybe I should just give in, plant only jugulone tolerant veggies, and maybe put in a few experiments :) Some things which were supposedly sensitive, I have grown under the drip line, and last year even right at the base of the tree.

    Bookmark   April 18, 2010 at 7:48AM
Thank you for reporting this comment. Undo

If the BW prove to be a damper on growth, you could container garden the veggies most sensitive to juglone, like tomatoes.

    Bookmark   April 18, 2010 at 9:08AM
Thank you for reporting this comment. Undo

harlgr8: with that question I looked up your page. I have grown gardens around BW for a lot of my life I have two going right now one Is getting quite large ay 30+ foot tall. Don't over think it, just find out what will grow in the sunny spots and trade or buy the stuff that don't. IMHO tomatoes may not grow at all However in high summer tomatoes are the easiest to find


    Bookmark   April 18, 2010 at 11:17AM
Thank you for reporting this comment. Undo

personal experience. I mix leaves with kitchen scraps for composting, no attempt to separate them, I have seen no effects.

    Bookmark   April 18, 2010 at 3:51PM
Thank you for reporting this comment. Undo
gardningscomplicated(southeast michigan - 5b or 6?)

glib - Thanks. I somehow missed the part about the leaves being composted first, when I read your earlier post. But I'm thinking a few black walnut leaves won't be too dangerous if they get mixed in with mulch. There must be some amount of juglone that can be tolerated. Otherwise not much would grow near my hickory tree.

    Bookmark   April 18, 2010 at 8:57PM
Thank you for reporting this comment. Undo

yes, in fact most everything grows around my hickories. Case in point: rhododendron is one of the most sensitive plants. One got zapped about 35 ft from a BW ( but with a main root going straight at it). The other manages in the shade of four hickories. So a little juglone is not so bad, and the leaves have a lot less than the roots anyway.

    Bookmark   April 18, 2010 at 9:34PM
Thank you for reporting this comment. Undo

I live in PA and have 12 large mature Black Walnuts on my 1.7 acres. I garden in 10-14" raised beds-veggies. I bought mushroom soil blended 50-50 with topsoil to fill them. No barrier underneath. The nearest tree is a young one about 15 ft tall and is about 20 feet away. Uphill is two large ones about 60 feet away. A small barn is between them and the garden. I have not had any problems with wilt as i had when they were in the ground. I think you are going to be fine.
have fun.

    Bookmark   April 21, 2010 at 8:45AM
Sign Up to comment
More Discussions
Giant Noble Spinach
I started this variety in my grow closet (which is...
Cucumber leaves turning white
Hi, I am totally new to having any sort of garden and...
Worth time and supplies to plant old seeds?
I have seeds ranging from one year to probably about...
Best kind of mulch for vegetable garden
What kind of mulch is recommended for a veggie garden?...
Can I use grape leaves as mulch?
I have alot of chopped and dried grape vine leaves....
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™