Answer: Wood ashes from hardwoods supply potash and can be used at a rate of about 5 pounds per 100 square feet. However, they are alkaline and should never be used where maintaining a lower or more acidic pH is an issue. Although I have not seen documentation with regard to black walnut ashes in particular, I would avoid using them just as I would avoid using black walnut leaves or wood chips in the garden. This is due to the adverse allelopathic effect that juglone, a substance contained in the black walnut tree, may have on other plants.
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