Does putting marigolds and nasturtiums in or near a vegetable garden deter pests from entering the garden area? Or is this an old wives’ tale; can it actually be harmful because those plants attract insects that will feed on the vegetables?

Native to Mexico, the sun-loving nasturtium (Tropaeolum) and French marigold (Tagetes patula) both attract and repel garden pests. While slugs devour both types of plants, especially immature French marigold plantings, many gardeners nonetheless use these species as companion plants to protect some of their vegetables. Not all marigold species, though, do the job. Only mature French marigold plants, likely grown in Mexican gardens long before Cortez arrived, emit insecticidal compounds that help control many garden pests. French marigolds are reputed to chase away white flies as well as keep tomato plants free from root nematodes and bean plants free from Mexican bean beetles. French marigolds are also unpalatable to meadow nematodes (eelworms).

Nasturtiums, once grown for the edible seeds that replaced capers when pickled, are considered by many gardeners, but not all, to be good companion plants to tomatoes, radishes, cabbage, and cucumbers. However, some gardeners think nasturtiums attract whiteflies, aphids, and viruses and should not be grown near plants that appeal to these pests. Other gardeners plant nasturtiums to attract these very pests so they will ignore nearby garden plants. Still other gardeners contend that the high sulfur content in nasturtium leaves repels pests such as aphids, squash bugs, striped pumpkin beetles, and woolly aphids.

The vibrant reds, oranges, and yellows of French marigolds and nasturtiums are a colorful addition to any garden. Moreover, both plants flourish in poor soil and full sun. However, while nasturtiums thrive on neglect, French marigolds need frequent deadheading for continuous bloom. Nasturtiums offer an added bonus: both their flowers and peppery-tasting leaves are edible.