This is one of those things that many people are not aware of, as you would have to be trying to grow tomatoes near Black Walnut trees to encounter such a gardening debacle.
Black Walnut trees emit a substance known as “juglone” that can damage and/or kill tomatoes along with several other plants, but most commonly the tomato plant. This harmful substance comes from the leaves, branches, walnut hulls, roots, and pretty much the entire tree. English Walnuts, Pecans, Hickories, and Butternut trees also produce juglone, but not near as much as Black Walnut trees.
The purpose or shall I say the advantage gained by secreting juglone, is the effect is has on inhibiting the surrounding plant growth near the tree itself – albeit there are still several varieties of plants & weeds out there that can grow near this tree. This process of releasing juglone into the ground, allows for these pesky trees to compete and combat any potential nutrient-robber around.
Walnut trees are nice to have, provide decent wood, and are worth a good dollar value and so on, but if you plan on having a garden, especially if you’re growing tomatoes, you need to take precautionary measures.
I’ve recently relocated, and last year I had to chop down roughly 8 to 10 of these lovely garden pests since I wanted to have a decent size crop this year.
The person who lived there before, could not understand why they never could grow anything or have good yield in the field that was surrounded by these trees. Upon moving into the area, I quickly realized what the problem was and, since I also built a fire ring, I got to chopping. I also cut down a few other trees as well. I used the Black Walnut wood to repair an old bridge, and I used the other trees for the fire ring. I saved some of the ashes from the wood I burned, but only from the trees that didn’t contain juglone, and used it for a soil amendment this spring, as I explained in my post titled “Organic Fertilizer – Natural ways to fertilize your garden.”
Anyway, back to the subject… If possible, simply grow your tomato plants and/or plant your garden far away from any Walnut, Pecans, Hickories, and Butternut trees. If you do decide to cut down the trees, remove the debris from the area. It often takes many years for these types of trees that emit this toxic substance, to effect your garden plants due to the slowly developing underground root system. Adding organic matter into your growing area, like a rich compost, will help enhance the microbes in the soil which, in turn, helps break down juglone and promote plant survival. One final note, as a gardener, you should always be on the lookout for any type of garden pests, potential problems or possible poisons near your garden and, as always, good luck with your crop……