Man has planted the fragrant marigold amid garden vegetables to deter everything from beetles to animals in search of dinner. According to Robin Howe and Beth Musgrove, of the Alabama Cooperative Extension System, although much of the effectiveness of marigolds in the garden relies on anecdotal evidence, marigolds do provide a method of controlling garden pests.
Marigold plants contain toxins that help eliminate root knot and other nematodes. Nematodes, tiny microscopic worms, damage the roots of vegetables, particularly tomatoes. According to Jeff Schalau, county director at the Arizona Cooperative Extension, planting marigolds reduces the number of nematodes in the soil the following year.
Although there is little evidence that marigolds repel insects, according to the Arizona Cooperative Extension, marigolds do attract beneficial insects, such as ladybugs, lacewings and parasitic wasps. These insects prey on harmful garden insects, providing natural insect control. What many gardeners perceive as the marigold's ability to repel insect pests may actually be a result of the beneficial insects they attract.
F. Robert Henderson, extension specialist from Kansas State University, reports that although it has not been scientifically verified, planting marigold borders around gardens may deter moles. According to WildLife & Natural History Q-line, marigolds may successfully deter deer.
Marigolds brighten the garden with their bright yellow and orange blooms atop bright green foliage. These highly scented plants release a pungent fragrance when brushed. Marigolds attract butterflies and other flying insects, adding both movement and beauty to the garden.