   Mesquite Allelopathy - November 25, 1998 Orville Gilmore, Yavapai County Master Gardener Arizona Cooperative Extension, Yavapai County I want to start this column with a story: Once upon a time many years ago I lived and gardened in Minnesota. There the soil was smooth and black and the rain abundant. In my memory, we dropped seeds in the ground in the spring and stood back to wait for the delicious corn, potatoes, beans, melons, or whatever. At least, that is what I thought I did-until the year I broke sod in the back yard for a new garden. It looked like good soil. There was a concord grape arbor to the east and a row of trees to the north, and the sun flooded in from south and west. I set my tomato plants in a row along the north side. Instead of thriving, they sickened and died. It was some time later that I heard, quite unofficially, that roots of the black walnut, the trees that were my tomatoes' nearest neighbor, exude a chemical substance toxic to tomatoes and some other plants as well. I didn't know whether to believe it or not, but I moved my garden out of range and had tomatoes once more. Something similar happened in my garden this summer. To give the nematodes a rest, I set out five tomato plants in the west end of the garden where I hadn't had tomatoes before. Four Champions and an Early Girl. The two Champions closest to the west fence died fast. The Early Girl, farther away, produced a tomato and faded. The other two Champions, farthest from the fence, grew enormously and are still (at this writing) producing fruit. What my Cottonwood tomatoes had in common with my Minnesota tomatoes was trees. On the other side of the fence are two small mesquite trees. Is it possible that mesquite and black walnut have the same effect on tomatoes? I checked the official literature and found nothing. Jeff Schalau, Yavapai County Agriculture Agent, checked his sources and also the Internet. Same result. All I found was a name for the phenomenon. "Allelopathy" it is called: the ability of certain plants to produce toxic substances in the soil that inhibit the growth of other plants. I have talked with people on the Master Gardener Line who wondered about the influence of mesquite trees on their gardens. To my everlasting shame, I told them I didn't think there was anything in it: "an old wive's tale." Now I'm beginning to wonder if the Old Wives don't know something our New Bulletins don't. Since I don't know the answer, I'm asking for help from you gardeners who have had experience with mesquite or other plants that seem to have an allelopathic effect. Let's put together some information from experience that will settle the issue once and for all. Call the Master Gardener line at 646-9113, ext. 14, or e-mail us at mgardener@kachina.net. Or stop in and talk with us at the Cooperative Extension Office, 2657 Village Drive. Let us know what your experience has been with mesquite or whatever other plants seem to suppress plant growth. And consider this: If mesquite is indeed the villain, does it appear to be due to the roots crawling into your well-watered garden? or the leaves or beans dropping onto the surface? or chemicals washed by rains from the tree onto your soil? |