Repel Tiny Garden Worms With A Simple But Overlooked Solution

An estimated 59% of all species on the planet live in the soil, and you can count the microscopic worm-like creatures called nematodes among them. Some nematodes are harmless to plants, and you can even use certain nematodes as a secret weapon to get rid of pests. Others, however, such as the root-knot nematode, are plant parasitic, and just may be the reason why your vegetable and fruit plants are in decline. One common strategy to reducing nematode numbers is to plant marigolds (Tagetes spp.) as a companion plant, especially with tomatoes. While this technique is time-tested, there's another related, yet overlooked, solution you might also try: growing marigolds as a cover crop.

Parasitic root-knot nematodes feed on a plant's roots, which in time will reduce a plant's ability to take in the nutrients and water it needs to grow. Marigolds, meanwhile, produce alpha-terthienyl, a substance that's damaging to the root-knot nematode. Because of this, marigolds are used as a trap crop, where the hope is that the nematodes will feed on the marigolds instead, but it doesn't quite work like this. Per the LSU Ag Center, nematodes will eventually find their way to the target plants.

Instead, you can try growing marigolds as a cover crop before your next growing season. In this way, the nematodes will have no other roots to choose from but the marigolds and their alpha-terthienyl. To try this method, grow the marigolds cover crop two to four months before you plan on growing your tomatoes or other plants. In that time, the root-knot nematode numbers, theoretically, should go down. After the few months of growing, cut the marigolds down to the ground before turning the entire crop over.

Before you put the cart before the horse, though, you might want to confirm if you actually have a root-knot nematode problem. While you might be able to observe some symptoms above ground (such as yellowing or a plant in general decline), you won't be able to confirm it's due to nematodes unless you test the plant's soil and roots for the presence of the microscopic organisms. To do this, you can send a sample to a local nematode-diagnostic lab. If it turns out you do have nematodes, growing the marigolds cover crops could help.

Crop rotation is something that farmers do all the time, and when growing a backyard garden, you have plenty of opportunities to use crop rotations and succession planting methods to increase your yields. So, for example, if you remove a bed of strawberries or onions midsummer (June or July) after the harvest, this is the perfect time to plant your marigolds cover crop. Remember, you want them to grow for two to four months before you till them back into the soil.

As for the planting, grow marigolds about 7 inches apart, with no surrounding grass. Remove any weeds that grow, too, as you don't want the nematodes to have a choice as to what roots they feed on. You want them only to choose the marigolds and their alpha-terthienyl. Note that French marigold cultivars are frequently selected for nematode control, including 'Tangerine' and 'Single Gold'.