I have cleared a 5000 sq ft space (100 x 50 ft) with the rows being 100 ft long. I am planning on planting one row of hazelnut trees, one row of blackberries, and one row of asparagus next spring. The soil is red clay so I am amending it with horse manure and lime. I saw a tree company offering free wood chips so I just got a trailer load of chips as well to amend the soil.
I did a plant ID on some leaves that I found in the chips and it identified it as pecan. I have read that pecan trees contain juglone. Does the mulch? How long would it take for the juglone to break down and be safe to plant?
Black walnut trees have the highest concentration of juglone in their buds, nut hulls, and roots but other trees related to the walnut (Juglandaceae family) produce some juglone as well. These include butternut, English walnut, shagbark, bitternut hickory, and the aforementioned pecan. In these trees, and specifically with regards to juglone in pecan leaves, the toxin is generally minimal and does not affect most other plant species.
So, the answer to, “Are pecan trees toxic?” is no, not really. There is no evidence that the minimal amount of juglone affects surrounding plants. It also has no impact when composting and makes excellent mulch due to its easily crushed leaves that are slow to decompose.
I don’t believe that the phytotoxicity of juglone has been adequately studied and the above linked article certainly provides no clarity to my mind- it is mostly about toxicity to animals and provides no links to research.
I’ve never had a problem with any mulch used on young trees, but starts in the vegie garden are another thing- anecdote suggests there can be a problem, at least to me.
How long before the mulch is safe for any garden use? I don’t know. Would soil incorporation increase any phytotoxicity to young trees and bushes. I don’t know.
I suspect that you could safely put large quantities below maybe 18 inches of soil to create a gradually decomposing base layer for mounds to vastly improve the drainage of a clay soil, or more practically use it liberally as a mulch, but incorporation should probably be tested unless someone on this forum has real experience using it this way. Shredding the mulch is going to speed the release of whatever juglone is in the wood. You could test it by stirring some into potting soil and trying to grow a young plant in it.
I have had extreme difficulty establishing peach trees near a couple of large old Carpathian walnut trees at one orchard I managed. but I eventually decided the problem was likely the huge competition of their extensive root systems more than toxicity, simply because the literature seemed to suggest that they didn’t produce all that much juglone. However, I can’t be certain.
Horticulture tends to be under researched if any given issue does not affect commercial production. Phytotoxicity is one such issue, IMO.
Personally, I’d not lose sleep over it. But I guess if one has special tree and there’s a 10% chance of it getting killed…
some folk might
lose sleep.