http://www.ces.ncsu.edu/fletch...
I made the mistake of cutting down a mature black walnut in my back yard when I first moved on my property. What I should have done is watch wait and see what this does exactly mean for that particular back yard shade tree. The tree was apparently much loved by former owners. It even had a well-used basket ball hoop attached to it. But I had it cut, thinking allellopathy meant that I couldnt grow other plants near the tree. Actually this is true only for certain plants, other plants, like blackberry for example, do fine in the shade of an old walnut tree. And the allellopathic effect is pretty specific to the area under the canopy of the tree.
Years later as a yearn for respite from the Southern heat, I realize that tree was planted on the south side of the house for that exact purpose--to shade the house from the hottest source of summer sun.