Good garden soil supports many living organisms besides earthworms, but worms play the most obvious role in soil fertility. Worms aerate soil with tunnels, provide nutrient-rich pathways for new roots to follow, and transform rotting organic material into fine pellets of natural fertilizer. Worm castings contain grit and clay as well as digested organic matter, bringing up minerals from deep below the surface to add to the topsoil. Adding worms to barren dirt accomplishes little unless preparations create a hospitable environment for them.
Turn over several spadefuls of soil down to at least a 6-inch depth. Break up the clods and look for worms. In healthy soil with normal moisture levels and nutrients, worms should already be active. Lifeless soil indicates other problems.
Take soil samples and order a soil test. Local agricultural extension offices provide this service; agents will recommend amendments based on test results. Worms avoid highly acid conditions created by regular use of ammonia-based fertilizers. Add lime to bring the soil PH back to between 6 and 7.
Provide worm food in the form of rotted vegetable matter. Till old leaves or lawn clippings as well as household garbage into the topsoil. Even cardboard or shredded newspaper works, though more natural materials provide more than bulk cellulose.
Prepare a safe zone for worms. Build a 6-inch-thick layer of damp rotting mulch in a corner of the garden. Worms need shelter from sunlight and predators and even established worm populations prefer to feed on the lower layers of deep mulch.
Release worms into the safe zone late in the evening. Scoop a hole in the center of the mulch, drop in the worms, and place the mulch back on top.
Cover the safe zone with hardware cloth or wire fencing and lay bricks or stones on the corners to hold the wire barrier down. The wire protects the worms from skunks and other night prowlers until they become established in the soil.