How to Control Nematodes With Marigolds

Overview

Marigolds not only add bright splashes of color and drama to the late summer garden, they can also protect other plants from soil-borne root nematodes. Using marigolds to repel insects has long been a part of folk wisdom, and now modern science is confirming what our grandmothers knew. According to the University of Hawaii, marigolds secrete chemicals into the soil around them that repels and controls microscopic insect pests in a process called allelopathy. Plant a barrier of marigolds around your vegetables or ornamental plants to control nematodes without synthetic chemical pesticides.

Step 1

Select marigold species with strong nematocidal qualities such as Tagetes patula, T. erecta and T. minuta. Determine which cultivars are best for your area based on day length and average temperature. For example, use short day varieties like "Cracker Jack" in lower latitudes with shorter summer day length to assure they will build up enough biomass before blooming.

Step 2

Plant marigold starts in rows spaced 6 inches apart around the entire perimeter of your bed or garden. Push loosened soil aside with the tip of a garden trowel and tuck the start into the soil. If you start seeds directly in the garden bed, take care not to disturb the young plants with strong irrigation spray, which can prevent them from rooting.

Step 3

Irrigate regularly to keep the soil around the marigolds evenly moist.

Step 4

Feed the marigolds with a balanced high-nitrogen fertilizer once a month.

Step 5

Turn the marigold plants into the soil at the end of the season and allow them to compost as nematocidal green manure.

Tips and Warnings

  • Avoid planting marigolds with plants which are particularly susceptible to thrips, gray mold and bacterial leaf spot, because these pests attack marigolds as well. In hot, dry weather, spider mites can attack marigolds. Varieties such as "Single Orange Scarleteade" are especially susceptible and should be avoided where mites are a problem.

Things You'll Need

  • Marigold starts
  • Garden trowel
  • Water
  • High-nitrogen fertilizer

References

  • University of Hawaii Cooperative Extension: Protecting Crops from Nematode Pests
Keywords: marigolds, nematocide, marigold insecticide, nematode control

About this Author

Malia Marin is a landscape designer and freelance writer, specializing in sustainable design, native landscapes and environmental education. She holds a Masters in landscape architecture, and her professional experience includes designing parks, trails and residential landscapes. Marin has written numerous articles, over the past ten years, about landscape design for local newspapers.