Dispelling Marigold Myths

1999 All-America Selections Winner: Marigold "Bonanza Bolero"
Photo credit: All-American Selections

In today's world of increasing eco-consciousness, many home gardeners are trying the age-old method of planting marigolds in the vegetable garden to repel pests.

Although the sunny annuals have been used in this capacity for many generations, little documentation exists showing marigolds actually repel insects. In fact, they may attract harmful pests damaging not only the marigolds but also your vegetables.

While marigolds are rumored to deter certain beetles, they are more widely known for their effects on nematode populations in the soil. Nematodes are microscopic worm-like organisms that destroy the root systems of plants.

Certain species of marigolds release compounds from their roots that are toxic to some species of nematodes. Unfortunately, the great variety of nematode species in Alabama soils significantly reduces the potential for adequate control.

When the right combination of marigold and nematodes species does exist, visible results can take up to four months to appear. During this time, if the marigolds are planted around or intermingled with your vegetable or ornamental plants, they can act as weeds, competing for water and essential nutrients and causing additional stress for the plants. Also, the marigolds don't draw nematodes away from the other plants, so the plants still run the risk of nematode infestation and damage. The greatest disadvantage to using marigolds is they attract large populations of spider mites to many gardens and landscapes.

If you enjoy growing marigolds, French dwarf varieties have shown the most consistent control (of nematodes, not insects!). Plant these marigolds in an infested garden and maintain a solid stand for three to four months to reduce nematodes. After the appropriate amount of time, plow the plants under as green manure. The nematode population should be decreased and the garden ready for planting. Be sure to keep the garden weed-free until planting time.

Rather than relying too heavily upon marigolds, a better approach to insect control is to use a combination of techniques. Most importantly, know the pests in your area and their plant preferences.

Also, remember that not all insects are bad! Identify beneficial insects and encourage these populations rather than destroying them. When buying plants for your garden, select varieties resistant to pests. Certain plants actually do repel insects; these plants should be intermingled with their more susceptible companions.

On the other hand, some insects choose to feed on one plant as opposed to another. Mix these plants with their less susceptible companions (your desirable crop)! Keep the garden weed- and debris-free. This will remove potential shelter for pests and ensure a healthier environment for plant growth.

When using insecticides, follow certain guidelines:

  • Do not use preventatively (only use when the need arises)
  • Target the specific pest
  • Get good coverage
  • Read the label!

    While marigolds provide some control, they are by no means a cure-all for insect problems in the garden. Employing combined techniques will provide more reliable and consistent control, and as a result, provide you with more tomatoes, peppers, squash and okra.

    SOURCE: Robyn Howe, horticulture student assistant, and Mary Beth Musgrove, Extension associate-horticulture, Alabama Cooperative Extension System (334) 844-5481.