Ok, I really did open up a can of worms, didn't i?
There's a difference between repelling and allelopathy. Plants can possess allelopathic qualities, not animals. A monarch butterfly eats milkweed, which is highly toxic, thereby acquiring the toxicity of the plant so no animal want to eat the butterfly - that's not allelopathic behavior. Planting marigolds around a garden will repel, but not poison, certain insects that might want to do your garden harm. Black walnut trees exude a toxin from their roots, called jugulone
, that has allelopathic qualities and will kill many plants living within its dripline. Some plants have a tolerance for it
, however, and will grow just fine.
I am going to post this same post over in Cindi's thread under the Farming section, we should continue it there, I guess!