Unwanted snakes, especially common garter snakes, may appear in the spring basking on your patio or front steps. Where did they come from?
Often, they've been hiding (or overwintering) in spaces behind or under concrete steps or patios. They gain entry through cracks or holes in the house foundation. These spaces provide warm (above freezing) places near or in the foundation wall for a snake to spend the winter. When spring returns, the snakes reappear outside.
Seal the cracks
Deter snakes from overwintering by sealing the cracks between the house and stoop or patio and filling holes or cracks in the foundation. If the cracks are not readily located, an energy audit company might be a source of help. These companies have specialized equipment to check for air leaks, which may indicate entrances for snakes. Most snakes can fit through a 1/2-inch-wide crack.
Fill cracks during the summer when snakes are not around, using tuck-pointing, expandable caulking, or other standard repair techniques. If cracks are filled while snakes are in the foundation, they may be forced to enter the house or die in the foundation and cause odor problems.
Eliminate their food source - Mice
Snakes may also appear in basements or garages. They may be looking for a place to overwinter, or may be searching for food -- specifically mice. By eradicating rodents from your home or garage, you will discourage hungry snakes from entering.
Mice can be controlled by removing their food sources, nesting sites, or by trapping them. Store dog food, birdseed, etc., in metal garbage cans with tight fitting lids, remove woodpiles stacked adjacent to or in the house or garage, and seal up cracks to prevent entry.
If using bird feeders around your home, try moving them further away to deter rodents that are attracted to fallen seed.
Certain types of landscaping may be appealing to snakes. Avoid using damp mulch or large stones; try smaller pebble or river-rock instead. Excessive watering of your lawn or garden may also attract prey items (worms, slugs, or frogs) that some species of snake feed on. Keep grass short throughout the yard. The larger the mowed area, the lower the chance of having snakes near the house. Short grass also makes it easier to see a snake in your yard.
Remove hiding spots
Snakes seek out yards that provide cover for both them and their prey. The easiest way to discourage snakes is to remove these hiding spots. Move any debris in which rodents might reside away from human-use areas. Trim shrubs and trees to create a space of at least 6 inches between the ground and the first branches.
The only way to absolutely keep snakes out is with fencing. Snake-proof fencing can be made by modifying a normal chain-link, picket, or split-rail fence. Attach 24-inch-high hardware cloth (1/4-inch weave) or aluminum flashing to the outside bottom of the fence. Bury the bottom of the hardware cloth or flashing 2 to 4 inches into the soil. Gates should have the same snake-proofing and be kept closed to be effective.
The fence has to go all the way around the yard. Snakes tend to travel along a fence rather than go over it. If the fence ends or has an opening, the snakes will enter the yard at this point. Fill any mammal burrows that appear near the fence.
If there is no existing fence, aluminum flashing could be used to encircle the yard. The flashing should be 24-inches high and buried 2 to 4 inches into the soil.