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| I have consistently found the presence of black walnut roots to be stunting to most common fruit trees and especially peaches. It is well known that juglones, a compound exuded by black walnut roots and fallen leaves, is toxic to many plants, but I had an interesting experience today when transplanting trees at two different sites that makes me wonder if that is the only way in which black walnuts are stunting.
At the first site there is a large black walnut near a small orchard I installed three years ago. I was adding a mulberry near it today. Although the orchard is a fair distance from this tree, its roots are incredibly thick where I planted the fruit trees before and where I planted the mulberry today- much thicker than the kinds of root systems that are sent out by other, similar sized forest trees- species like ash, maple, oak and tulip. The fruit trees have not established as quickly as usual- they are growing, and I am confident they will eventually thrive, but it is taking a while. At the second site there are no black walnuts, but there are two very large, cold- hardy pecan trees whose roots tightly weave through the soil in the same manner as the black walnuts at the first site. It is a fairly large home orchard with most fruit trees beyond the range of these roots, but in the area where they do dominate it has been a kind of Bermuda triangle for peach trees over the last several years. At first, after planting, the trees are fine, but by the third year they would quickly go into decline and out of productivity, barely surviving. In the process of planting I would create wide holes where competing roots were cut back a significant distance, which seemed to prevent the peach trees from being stunted at first.
Today I transplanted one peach tree from that site to see if I could get it to flourish where those black roots aren't present. This tree had barely grown since I put it there 3 or 4 growing seasons ago- or so I thought. At least the top hadn't grown much. When I began the process of bare root transplanting it I was extremely surprised at how massive the roots had become without coinciding vigorous top growth.
It took me four times as long to transplant as I expected and I have never seen such a great looking root system attached to such a pathetic tree. The annual shoots were not more than 3" long and there weren't enough of them.
At any rate, I find it quite amazing that a tree can be thoroughly stunted on top while growing a very substantial root system. Clearly that root system was not functioning well and I wonder if the stunting was the result of toxins or just an extraordinarily competitive species grabbing most available water and nutrients from the soil at the expense of less competitive trees. If it is the latter and pecans and black walnuts have similar root systems, maybe there is more at play than allelopathy when black walnuts stunt other plants. |
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| Rootstocks are usually selected for aggressiveness. Maybe it has something to do with differences in the rootstock variety and the scion as to their environmental tolerances (and juglone?). Sounds like the root system usurped all the carbohydrates produced by the scion and starved the top! hortster |
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- Posted by harvestman 6 (My Page) on Thu, Dec 1, 11 at 14:07
| Of something more is a typo. Should read or something more. |
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| Do you know which cultivars the scions and rootstocks are? Are there other trees on site (or elsewhere, that you are familiar with, for that matter) with the same scion/rootstock combo? Have the rootstocks been suckering significantly? You don't happen to have pictures do you? This does seem kinda weird. |
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- Posted by harvestman 6 (My Page) on Fri, Dec 2, 11 at 5:26
| I don't record peach rootstocks but they are probably all on Bailey which is the most commonly used by ACNursery and Hilltop- the two commercial suppliers I use for my nursery. For peaches scions don't make so much difference but there are about 10 different varieties I've tried in this area- the one I dug up was a Red Haven. If the client wants me to dig up more trees I'll take a picture. |
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- Posted by tsugajunkie z5 SE WI (My Page) on Fri, Dec 2, 11 at 6:12
| Just about all plants in the Rosaceae family (peaches) will have an adverse reaction to juglone. Walnuts also can have very fiberous roots (similar, though not as bad as maples) that suck the life out of the soil creating a double whammy for plants. Whether the large root systems were an attempt to find nutrients might be determined by a soil test but rootstock selection is also certainly a possible factor. tj |
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