Marigolds are one of the best plant allies for garden vegetables and fruits due to their ability to repel or kill insects and larvae that may feed on or damage crops. Marigolds are mostly pest free and are considered easy to grow, low-maintenance annuals. They bloom throughout the heat of summer, preferring a site with full sun and good drainage.
Types of Marigolds
African marigolds (Tagetes erecta), also known as American marigolds, are taller plants that produce large-sized double flowers. French marigolds (Tagetes patula) are a bushy type with smaller flowers. They are suited to rainy conditions. Pot marigolds (Calendula officinalis) are not considered true marigolds, but offer some of the same protection as true marigolds. Pot marigolds may not stand up to intense summer heat, but they do have the additional benefit of producing edible flowers.
Marigolds not only repel cabbage moths, chemical exudates from the flowers and foliage of marigolds have proven lethal to Mexican bean weevils, and marigold root compounds kill cabbage maggot larvae. The odor of marigold plants is unappealing to pests, and the roots emit a substance that repels many types of nematodes. Marigolds “can suppress 14 genera of plant-parasitic nematodes,” according to the University of Florida IFAS Extension.
Marigolds attract beneficial insects to the garden. These insects feed on or parasitize insect pests that may trouble your crops. Marigolds attract lacewings, lady beetles and parasitic wasps.
Root-knot nematodes attack a variety of crops, and no chemical controls exist for use in home gardens, so marigolds are a valuable tool for gardeners. Growers can plant African or French marigolds as a cover crop. Planted before other garden crops, marigolds release alpha-terthienyl, which has an allelopathic effect. These marigolds can control populations of root-knot nematodes and provide the additional benefit of reducing some fungi, bacteria, viruses and insects that may lead to plant diseases.
Marigolds are plant allies that you can pair with eggplants, potatoes, pumpkins, tomatoes and squash plants to provide the benefits of protection or improved growth. Marigolds deter Mexican bean beetles from damaging beans, discourage Japanese beetles from harming corn and deter beetles from causing harm to cucumbers, melons, pumpkins, squashes and potatoes. Marigolds help prevent nematodes from affecting eggplants and tomatoes. Pot marigolds deter beetles from visiting asparagus plants and tomato worms and general pests from bothering tomatoes.
- Clemson Cooperative Extension; Marigold; Karen Russ; March 1999
- University of Florida IFAS Extension; Marigolds (Tagetes spp.) for Nematode Management; R. Krueger, et al.; 2009
- Utah State University Cooperative Extension; Utah Pests News -- Companion Planting: Myth or Reality?; Marion Murray; 2010
- North Dakota State University Cass County Extension; Companion Planting; Todd Weinmann
- Seeds of Change; The Cutting Edge Newsletter -- Companion Planting: So Happy Together!; Kelle Carter; April 2006
- Arizona Cooperative Extension; Backyard Gardener -- Marigolds and Nematode Management; Jeff Schalau; June 2004