As we know more about plant growth and plant interactions we are learning how neighboring plants can affect plant growth. According to University of Florida Extension a chemical called ailanthone, isolated from Tree of Heaven, reportedly possesses herbicidal activity similar to glyphosate and paraquat. Glyphostae is the stuff found in Round Up™. A once common garden practice was to follow crops with rye or wheat. We now know both of these chemically suppress weeds when used as cover crops or when crop residues are used as mulch. Broccoli residue interferes with growth of related crops such as cabbage or cauliflower that follow. As we understand these natural herbicides we may be able to include them in our garden practices to reduce weeds.
Black walnut is the poster child for not being a good neighbor. Black walnut trees naturally contain a chemical called juglone which can inhibit the growth of some plants. The largest amount of juglone is found in the walnut's buds, nut hulls and roots. However, even walnut leaves and stems contain a small concentration of juglone.
The largest quantities of juglone are usually right under the tree's canopy. Some sensitive plants may live near a black walnut, but will not live directly under it.
The amount of juglone present also depends on soil type, drainage and soil microbes.

Who would have thought something as innocent as a black walnut tree could inhibit another tree or plant? It’s not really its fault. It was just made that way!

However, for any prepper that plans to create their own garden, to pull leafy lettuce and ripe tasty tomatoes out of the ground, you may first want to do some research into the flora and fauna about that bed of dirt. As it turns out, gophers are not the only pests you may have to worry about!

For more information go to the University of Illinois Extension.