Worms serve two purposes in the garden: they burrow in and loosen the soil, aerating it and making it easier for plants to extend their root systems; and they consume organic matter in the soil and convert it into nutrient rich worm castings that nourish plants. Worms can also be used for composting, called vermiculture, which produces worm castings that can be used as fertilizer for house plants and garden beds. Two kinds of worms may be found in your garden or yard: earthworms, which burrow deep into the soil and are usually found close to the surface after a good rain; and red wigglers, which consume organic matter at a faster rate than earthworms and live closer to the surface.
Place a piece of wet cardboard on top of the lawn or soil in the evening. Red wigglers love to feast on wet cardboard, so you have just served up a gourmet meal for your garden worms. Red wigglers consume organic waste even more quickly than earthworms.
Pick up the cardboard in the morning and look beneath it. As the name implies, red wigglers are reddish brown in color, and smaller than earthworms. They are 3- to 6-inches long and very thin. They live in the top 3 inches of organic matter, and do not burrow as deep as earthworms, so they are better for composting than they are as soil conditioners.
Gather earthworms from your garden in the early morning, after a night of rain. The moisture brings them to the surface, so a careful inspection of the ground should be productive. Earthworms are long and plump, and grayish in color, with a darker, brown patch toward one end. An earthworm can eat up to half its own weight in organic matter a day.
Select worms that will fit your purpose. Add earthworms to your garden for aeration, or gather red wigglers to add to your worm composting bin.