What Flowers Keep the Garden Free of Voracious Nematodes?

Nematodes

• Nematodes are organisms that live in the soil. Most of them eat bacteria, fungi and other harmful organisms. However, some nematodes — root knot and plant-parasitic — damage plants. The harmful nematodes attack plant roots, reducing the plant's ability to absorb water and nutrients. Symptoms of harmful nematodes include yellow foliage, wilted leaves, stunted growth and premature death. However, other conditions, including disease, environmental factors and other pests, can cause similar symptoms.

Marigolds

• French marigolds (Tagates patula) and the ordinary marigold (Calendula officinalis) get rid of root knot nematodes. The French variety keeps them out of the area for several years after planting. Closely plant an entire area with French or ordinary marigolds for a season, and take the spent flowers and dry them out. Remove the seeds from the dried flowers, and store them in a plastic bag for the next growing season.

Dahlias

• Dahlias are a lesser-known flower to control nematode populations. The rhizomes in the root system repel nematodes. Companion planting of these flowers with plants more susceptible to nematodes can reduce or eliminate nematode damage. Dahlias have a wide variety of shapes and colors, making them compatible with almost any landscape. Dig up the dahlia’s tubers at the end of the season, and store them in plastic bags with moist peat moss. Moisten the peat moss periodically, and replant the dahlias the following spring.

Soil Solarization

• Soil solarization works by using the heat from the sun to kill nematode — and other pest — populations. Before solarizing, break up and moisten the soil. Cover the area with a clear plastic tarp, and bury the edges. The plastic will hold in the heat and kill nematodes, weeds, fungi and other pests. Let the area sit for at least six weeks, and do not uncover it until you're ready to plant. Soil solarization works best in the hot months, and is effective from 6 to 8 inches beneath the surface.