Nematodes are microscopic worms that live in the soil. While there are many kinds that are beneficial, feeding on fungi, bacteria, and other organisms, some harmful nematodes feed on plants. These plant-parasitic nematodes damage root systems and reduce a plant's ability to get water and nutrients from the soil.
When nematode populations are large, you may see signs of their damage on your plants like yellowing and wilting. If planted into beds that already have high numbers of nematodes, plants may become stunted and slowly die. Transplants may not grow at all after planting. Nematodes also can damage below-ground edible plant parts we intend to eat, like carrots or potatoes.
To battle harmful nematodes, purchase plants and seed that are labeled nematode-resistant, and consider solarizing your soil during the summer prior to planting.