The bright marigolds flanking my doorway and alternating with the vegetables in my garden provide much more than a cheerful bit of color. Indeed, marigold uses are so wide-ranging that their function as decor is almost surpassed by their other services!
Most gardeners are aware that marigolds’ pungent flowers and foliage discourage many insects from feasting on nearby crops. But even the odorless varieties are effective: Planted as a border around the garden or in rows next to the vegetables, they act as a trap crop for Japanese beetles. Since those noxious insects like to congregate on the flowers, the gardener simply can shake the collected pests into a can of kerosene, where they’ll expire.
Meanwhile, the marigolds are just as hard at work underground, controlling nematodes (those tiny, eel-like worms that attack the roots of plants). While scientists can’t explain how the plants affect the subterranean spoilers, they do admit that marigolds are effective! In comparing the soil of two plots, one with marigolds and one without, researchers at the Connecticut Agricultural Experiment Station (and at other agricultural labs as well) discovered 75% to 85% fewer nematodes in the flowered plot. Apparently, a substance is exuded from the little plants that deters these almost invisible crop-destroyers.