toxic

In the backyard, in our communal vegetable garden, neighbors have already started stacking piles of leaves and cut grass. A neighbor and I are planning a trip to a local horse stables to get piles of manure, mixed in sawdust. We'll mix that with the leaves, somewhat shredded, the cut grass, and strips of newspaper. This should make a nice compost for our garden. We've puts lots of bags into the soil, but it is still extremely hard.

The important thing to remember about using leaves for compost is to avoid black walnut tree leaves. Black walnuts put a toxic substance in the soil through their roots and through their decomposing leaves. Once the toxic stuff is in the dirt, it won't just wash away, but will remain.

One effect of the substance is that it retards seed germination and plant growth of several different plants, particularly vegetable plants. It's very hard to grow tomatoes around black walnut trees. Your local agricultural extension service should have a list of plants affected by black walnuts. But here's a nifty two page article from Purdue (PDF) that outlines all you need to know about black walnut toxicity.