In warmer southern areas, the snake is active year-round; otherwise, it hibernates in common dens, sometimes in great numbers. On warm winter afternoons, some snakes have been observed emerging from their hibernacula to bask in the sun.
Garter snakes generally mate in March or April, after hibernation. The species is oviparous; females give birth to a litter of 12-40 live young anytime from July through October.
If you own a common garter snake as a pet, a 15-25 gallon tank should be enough for one adult snake, baby snakes can live in a 5 gallon tank, and young ones (1-1.5 years) can live in a 10 gallon tank. As the snake ages and becomes more active a 10 gallon tank will be insufficient as they need more room to roam around than a 10 gallon tank provides. Garter snakes will become weak and depressed if they don't have enough room to roam. Always be sure the lid is very secure and has a small enough mesh so the snake cannot escape.
Bedding should be one of the following things: newspaper, paper towels, pine or aspen shavings, "AstroTurf", reptile carpet or other commercially available reptile bedding. Do not use only sand, as these snakes are not a desert species and do not do well on sand; getting sand in its eyes and mouth can kill them. Adding a shallow bowl of clean, dechlorinated water to this tank allows the snake to drink and swim. This water should be changed every day because a garter snake will defecate and urinate in the water and then will drink from it, which causes many illnesses.
Decorations should include many things for the snake to hide in or under, plus a few rocks or ledges for basking in the light. Live plants are not necessary and often their care is inconsistent with a snake's needs (humidity, fertilizing, light and heat needs, etc.), but fake ones will make the snake feel more natural.
Heating can and should be done two ways: a heat mat, sold for reptiles, and a heat lamp or ceramic heat emitter. The mat it is placed under the tank on one end (never the middle) and the heat lamp is placed above the tank. The emitter is sometimes better than a light because Garter snakes are sometimes shy and dislike bright lights, but a lot of garters will learn to love the lights, so experiment until you find what your snake likes best. Place the heat lamp directly over the tank; you will have to adjust the height until there is a temperature range of about 70 F on the cool end (away from the heat mat) and maybe 75 to 80 F on the hot end (with the heat mat).
Use two thermometers, one on each end, to monitor the temperature. During the night time, it would be best to turn off the emitter or light, unless you do not have a mat, because Garters like a little fluctuation in temperatures, but be sure that the hot end never gets below 70 F at night, because this may put your snake in danger of death or at the very least cause him to start hibernating, which is dangerous in itself because he will not eat when he is hibernating, even if he does "wake up". Be sure to put some shade on the cool end so your snake can get cool off if it wants, but allow room on the warm and cool ends for your snake to get comfortable. Remember, its his world you are setting up, so make it a nice place to live. Feeding is something that is widely debated, but the generally accepted foods include pinkie mice, known outside the reptile hobby as newborn baby mice, alive will entice feeding, but prekilled is just fine if the snake will eat them, also good are earthworms which are best to be obtained from a bait store, you must be very careful with these as they are sometimes raised in unclean conditions and may transmit bacteria to your snake. Also feedable are guppy fish, however, feeder goldfish are often raised in extremely dirty conditions, as they are hardier and "easier to abuse" than guppies, so you should not feed goldfish unless you can arrange to check the animals over a period of time for illness. There is also a debate over thiaminase, with goldfish contain, and wither it will make a garter snake ill and die if the snake is fed solely goldfish, as thiaminase depletes vitamin B. Any fish should be fed in a shallow bowl with water, but not the swimming water that you have permanently in the tank, take the food bowl out after the snake has eaten. Foods generally not acceptable are crickets, dusted or otherwise, as Garter snakes in the wild would never eat them and the sharp exoskeletons are hard on Garter snakes, if they even accept them in the first place, so feed these with caution. Young garter snakes often benefit from eating wax worms and mealworms for extra fat boosts, but in general they should only be given as a treat to adult snakes, as it causes obesity. Feeding is generally done twice a week, but if you have a younger snake, feeding should happen more often, up to every other day. Handling is possible, but should be done carefully, because Garter snakes are very delicate and skittish at first, especially a wild caught one. They will sometimes secrete a foul smelling musk from their cloaca (the breeding/defecating/urinating area near the tail end of the snake) This is to make you let him go because he is scared you will eat him. Do not let him go unless you are absolutely too repulsed by the musk, as this will send a message to the snake that it worked and he will keep doing it. In general continue to gently restrain the snake until it is calm and then re place it into the tank and leave it alone for a couple of days. After a while it will stop musking you and calm down because he will learn that you will not let him go unless he is calm. Some will even enjoy the warmth or your hands and will enjoy being handled. Garter snakes should never be let roam around the house because they can find any number of small spaces to crawl into and escape or be suffocated/crushed/starved to death when you can't find it again. Children should not be allowed to handle a garter snake unless you supervise, as children can squeeze a snake to death or break its back, or any number of horrible things, plus salmonella is an issue if the child kisses the snake. Always use hand sanitizer after handling the snake.
Current scientific classification recognizes thirteen subspecies: