Insert the thermometer 8 inches into the soil in your garden to test the temperature. If the thermometer reads at least 54 degrees Fahrenheit, you may safely apply the nematodes to the soil.
Rake the soil to remove debris, and clear a path to apply the nematodes.
Purchase nematodes from a garden supply shop, and keep them in the refrigerator until you intend to apply them to your garden. Place the nematodes in a watering can filled with water. Be sure the watering can has spout holes large enough for the nematodes to pass through. Stir continuously to prevent the nematodes from sinking to the bottom.
Pour the nematodes over the garden area that needs pest control. Cover the path that you treated with a rake. Repeat every month until snails and slugs cease to pester your garden.