Mobility of juglone in soil/water

Hi all,

i am breaking my head about where to put the persian walnut on my plot.

As they become rather high, it makes sense to put it in the northern part of the food forrest,
however as the terrain slopes to the south i am a bit afraid that the juglone might be washed all the
way to the southernmost point of the FF, killing the not so juglone tolerant trees there.

As the landscape ist karst i suspect there are also underground streams that might
contribute to the issue even more.

Is there any data of the mobility of juglone in soil/water?

Hi R. - I can't answer your specific question, but I researched juglone for a friend, so I knew that there were at least options for growing things under the drip line of a Black Walnut.

https://findingseaturtles.com/juglone-tolerant-shade-plants/ - most of these are flowers, but some hostas are edible, and flowers do support our pollinators and helpful insects

https://www.mortonarb.org/trees-plants/tree-and-plant-advice/horticulture-care/plants-tolerant-black-walnut-toxicity  - this article has lists covering trees, shrubs, vines and forbes that are Juglone-tolerant

What neither of these articles seemed to say is whether those plants just tolerate the Juglone, or actually decompose it. I've seen one passing reference suggesting that Juglone does not persist over winter, but other places suggest that dead roots will excrete it, which suggests to me it is persistent.

You may just have to experiment and report back! I would suggest you do a "barrier" down hill of the tree of the great variety of tolerant plants in the second link I've provided.

Good luck!

i think if you’ve got a tree annually shedding leaves and exuding from the living roots, it’s automatically pretty persistent. or continuous, anyway.

that said, there are more and less sensitive plants. while roots extend beyond the dripline, i’ve got doubts that juglone travels all that much, loose in the soil...but then i think juglone sensitivity gets overstated a lot. i suspect if the plantings nearer to the walnut are relatively resistant, you won’t notice much ill effect if any.

It's where the leaves fall and roots are.  Nightshade family (potatoes, tomatoes, peppers) is most? affected by juglone.  about 1.5 the size of canopy.  Effects can last up to 5 years.

you can plant corn, sunflower, legumes, etc right into juglone areas.  Pecan plants are in same family as black walnut, and one should be concerned about where pecan leaves land.

I have read about apple trees being killed up to 60 feet away by a walnut tree.
So even if it does not kill it, juglone might weaken it so that pests attack.

Anyway my site is specific (karst) so that if juglone is water soluable there is
a high propbability it will be present downslope if i plant a walnut upslope.

This is why i ask whether it is water soluable.

I believe that the Persian walnut (juglans regia) has less issues with juglone than the black walnut. I can't find a reference for that just now though I'm sure I read it somewhere. They do have juglone still and according to Ken Fern:

Plants produce chemicals which can inhibit the growth of other plants. These chemicals are dissolved out of the leaves when it rains and are washed down to the ground below, reducing the growth of plants under the tree

So it sounds like the juglone could potentially be quite mobile in the soil. I thought about it a bit before I planted mine, since I have pretty shallow soil, then I thought I'd just go for it anyway! I have tried to plant them a little away from my vegetable growing areas and will let you know in 20 years time whether they seem to have affected my other trees
I now have 5 walnuts, although one is looking a little sickly, but others are already trying to flower!

I'm not an expert, and have no scientific knowledge. I do have practical experience. We have lived in our house for about 30 years. For about 23/24 years of it we were literally surrounded by walnut orchards. They were English walnut, but all were grafted to a black walnut rootstock. Since that time the west orchard was removed for a house 😞. The north orchard is now almond.  We had 4 walnuts in our yard. One is huge.  One the English walnut died and the black walnut grew, and one my son cut down only to have the black walnut regrow 3 times now.  I have always had a garden, always grown fruit trees. Peach, apricot, plum, apple, cherry (only managed to grow the last couple of years). I also grow grapes, blackberries, and raspberry.
The black walnut that keeps growing back is about 15 feet away from my main veggies garden. The raised beds are all hugel beet style, so odds are there may be black walnut roots in or near them.  I'm very proud of my garden and always amazed how much I can grow. Not only might there be roots, but lots of leaves in the fall. Not to mention the squirrels constantly planting walnuts in all loose soil.  I'm forever removing little walnut trees from my garden.
I have had lots of failures over the years, but I don't think any of them were because of the walnut.  I hope this helps. Good luck