Three years ago we purchased property with lots of black walnut trees. Besides making a mess of our yard, we have to be careful what we can plant. We have taken most of them out; there may be just a few left (we have a very wooded lot). My question is how long will the ground continue to hold the toxicity from the trees we have taken out?

Greetings, Walnuts produce the juglone as a defensive strategy as they grow so slow. Walnuts will continue to produce this as long as they live. The material begins to break down after the tree is dead or removed. Lots of speculation exists on how long, some suggest just months, others years. Some suggest Juglone will persist until the the roots are completely decayed. One indicator that the juglone is gone or at least reduced in strength is the kinds of weeds that are beginning to grow in that areatht were not there before. For example tomato plants are very sensitive, so it they grow, the juglone is likely gone. Othe sensitive plants are petunia and peony. Grass seems very tolerant. Soil seems to also play a role in how fact juglone breaks down. Soils with good aeration and microbial activity, juglone breaks down quicker.

I hope you find this information helpful