Nematodes are tiny roundworms that are not harmful to humans or pets. According to Nematode Nick's Landscaping, nematodes are predators to more than 200 species of insect. One of those insects is the Japanese beetle grub, which is known for causing brown patches in lawns. If you find that you are having an insect problem in your soil, you can add nematodes and they will kill the insects for you.
Prepare to use your nematodes within two weeks of purchasing them. Make sure you store them in the refrigerator and keep the sponge they are in moist until you are ready to use them.
Use the nematodes when the soil temperature is between 55 and 85 degrees F. It is also best if the nematodes are sprayed into the soil later in the day, when the sun is not as hot, versus first thing in the morning.
Water the soil where you intend on spraying the nematodes. A light application of water is all you need.
Mix your nematodes with water in a backpack sprayer as specified on your product label. This will vary based on how many nematodes are in the package you bought.
Spray the nematodes on the soil where you were having the insect problem. There is no trick to this, just make sure you are spraying the soil around the plants, and not the tops of plants. The nematodes will live in the soil. Spraying the nematodes on the plants won't hurt the plants, but the nematodes will not be able to get into the ground where they can do their job.
Water the area where you sprayed the nematodes again, and continue to give the area a light application of water for the next three days.