Answer: Black walnuts give off a substance from their roots that is very damaging to some plants including tomatoes and grapes. The leaves and husks have less concentrated amounts of the substance, but should be avoided as a soil amendment in the future. I would suggest you try to locate your tomatoes in a different area. Even though the leaves will break down fairly quickly and in a season the soil would be free of any substances they contained, the roots will continue to make the spot uninhabitable for tomatoes.
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