Like most others here so far, my experience is essentially Black walnut (and Butternut). Those are precocious enough that when squirrels plant them inside almost anything else, they’ll shoot right up. If your other trees are already there, they would not interfere with the walnut finding its place. I presume other walnuts would be as happy to find place. My two English walnuts were grafted onto J nigra and I’m fairly certain the second will be following the first into the grave by the end of summer.
I have several pawpaws in range of the black with no concern so far (three years and growing) and the wildlings the squirrels are attempting to cultivate have assorted wildling cherries, oaks, and maples (probably Norway) all within a couple feet with no issues. One lonely little dogwood as well. I just gave it an increase in sun last month, so maybe I’ll know what type that is this year, but hte nearest known are Kousa.
Trev, muscadine and pawpaw are both highly tolerant of juglone. If you ever want to see something interesting, try spraying muscadines with roundup. Hint, they slow down for a few weeks, then grow twice as fast to make up for lost time.
There may be a lot out there for juglan nigra, but it is much harder to find good detailed information for juglans Regia. When I search it always turns into results for juglans nigra. I am interested in the juglans regia. I liked the under canopy list, but it didn’t cover juglans regia and I can’t find anything that actually says what level of juglone they produce. I can find information for juglans nigra like is said, but I still feel unconfident in my selection process. I would like a little more freedom to choose varieties than the high juglone levels that juglans nigra would limit me to. If I could find a document that said how much juglone each variety produces then I could use your document for under canopy plants to determine which would be good options in my case, but when I search for something like that I don’t find anything. Maybe, it hasn’t been researched enough yet, or they see it as to relative to plant size. Maybe, the answer is already out there and I am just missing the research in my searches.
It has been almost 30 years since I read this, but Regia on Regia rootstock produces between 1/4 and 1/2 as much juglone as Juglans Nigra. This was published in one of the NNGA annual reports back in the 1960’s. Caution that Regia on Nigra rootstock produces as much juglone from the roots as pure Nigra. Paradox rootstock also produces similar amounts to the J. Hindsii parent which is very similar to J. Nigra.
Do you know how much a pecan tree produces? The Persian walnut didn’t show up on the list of compatible plants, but the pecan tree did. Thank you for the helpful info though. Do you happen to have a link for the juglone levels?
I don’t know how much a pecan produces, but it does produce some juglone. Pecan trees are generally tolerant to juglone. Pawpaw also is extremely tolerant of juglone. I saw large pawpaw trees happily growing under Gerald Gardner’s 30 to 40 year old walnut trees when I visited him in 2003.
I don’t have a link for the amount produced. As I stated, this was published in an NNGA annual report from the 1960’s. I bought a set of annual reports going back to the 1950’s and then read all of them. You can get a set of annual reports on a thumb drive from the NNGA librarian for about $150 the best I recall.
This entire process is only partially understood, and a significant amount of it depends on how aerated the soil is able to be and proximity of roots to the substances that coincide with juglone, which itself has precursors that may be part of the problem for part of the affected plants. i.e. juglone has seen a lot of study, but it is not the only allelopathic substance at play and results focusing on it alone have not been consistent. I don’t think they’ve really tried to differentiate “safe” based on various species.
If you can ensure segregation of roots and good aeration, you’re significantly better off. Water does not flush juglone away or contribute significantly to the spread. Oxygen appears to be required both to turn precursors into juglone and to break it down. Thus, greater concentration requires better oxygenation. Assorted bacterium/mushroom also break it down, and we all know what some of our landscape trends do to obstruct healthy populations of those.