Slugs and snails (the former have no shells) hide under stones, leaves, and debris during the day to keep the sun from drying them. At night they emerge to feed, leaving telltale trails of silvery slime. Get rid of their hiding places by keeping your garden cultivated and clean.
To trap slugs or snails, put out grapefruit or potato halves, cabbage leaves, or even wide boards for them to crawl under. In the morning collect the pests and drop them in soapy water. Or set out dishes about 1 inch deep of beer or grape juice level with the soil; the creatures will crawl into them and drown. Don ‘t kill garter snakes; slugs are among their favorite foods.
Protect seedlings and leafy plants by surrounding them with sand or by spreading rings of wood ashes or lime well away from the stems; the pests won’t cross them, although these materials will have to be replaced when they get wet. To shield a vulnerable plant, remove both ends of a tin can, tape a sleeve of window screening to it, and sink it into the soil.
Poison baits are often effective; but they are hazardous to children, pets, and wildlife and can be spread by rain or by watering. Only use baits labeled safe for fruits and vegetables, and protect the bait from water.