Catch Your Snake or Purchase From Breeder

First you need the snake or snakes for me I caught mine as baby's but some breeders sell garters like: http://www.backwaterreptiles.com/garter-snakes-for-sale.html it sells a wide variety of snakes there garter snakes include: northern garters, black necked garters, albino checkered garters, and ribbon snakes. The easiest kind to find are northern garters which I suggest because they are more common in the area so the very well adapted to the climate

Step 1: Housing Your Garter

It is quite easy to house garters as long as the lid fits tightly on because they are escape artists. First you need to get your supply's I suggest getting them from Petco they have the best supply's for reptiles. What supply's you need: a large tank*,food and water bowls, decor (optional but recommended),and a hideaway. *Cage size: A baby garter snake’s cage should be no larger than five gallons (and could even be half that size); in general, a garter snake less than a year old can live comfortably in a five-gallon tank. An adult male about 60 cm (two feet) long will do well in a 15-gallon tank, and a full-grown female or a breeding pair should be all right in a 25-gallon tank. More room is certainly better within reason, and you’ll need more room if you’re using a planted terrarium instead of basic caging, but it’s very unlikely that a single garter snake will ever need anything more than a 35-gallon tank. Substrate and cleaning:
Substrate is what you put on the bottom of the cage. Many different kinds of substrate are possible: everything from a planted terrarium to paper towels or butcher’s paper. Other popular substrates include wood shavings (aspen is best, pine is probably all right, but never use cedar), cypress mulch, bark nuggets, or indoor/outdoor carpet.

Planted, naturalistic terrariums may be pretty, but a simpler cage is easier to clean. Garter snakes defecate frequently, and unless you change or clean a garter snake’s cage frequently, the cage will smell quite ripe in short order. It therefore makes sense to make the cage easy to clean! I recommend keeping them on paper towels, which can be replaced cheaply and quickly when soiled.

You shouldn’t have to change the cage more than once a week. More snakes in a cage will make it messier faster, of course, and a fish- and worm-based diet is messier and smellier than a mouse diet — either of these circumstances will necessitate more frequent changes.

If you use paper towels, it’s enough to replace them when soiled and rinse off the glass where the snakes have soiled it. If you use shavings, mulch or bark, pick out the urea and feces when you can, then change the cage completely every two to three months or so. Clean the cage thoroughly, using detergent or bleach, or both, every once in a while.
Heating and Lighting:
Snakes are cold-blooded. This means they need external heat to run their body metabolism. A snake that is too cold is not only sluggish, it’s also unable to digest its food properly: it may refuse to eat or even throw up its food. A pregnant snake also needs warmth for her babies to incubate.

In general, snakes need to be a little warmer than room temperature. This is especially true in an air-conditioned home, where room temperature is frankly pretty cold. But they don’t like it uniformly warm, either, and it’s actually more dangerous to the snake if it’s too hot than if it’s too cold.

The ideal temperature for most snakes is in the 25-30°C range (about 75-85°F), but it’s important that the snake have the option of warming up and cooling off when it chooses. You give that to your snake by heating one side of the cage, creating a temperature gradient.

You can use a heating pad underneath one side of the cage, or an incandescent or reflector bulb above it. You can use a commercial reptile heating pad, or you can use an ordinary electric blanket, which is less expensive, turned to the lowest setting. Fluorescent bulbs provide light generate little to no heat.

Keep an eye on the heat with a thermometer. Stick-on thermometers aren’t terribly accurate, but they give you a general idea. It’s not important to achieve precise temperatures — remember, these snakes encounter all kinds of temperatures in the wild. As long as it’s somewhere between 22°C (72°F) at the cold end and 30°C (86°F) at the warm end, you’re probably fine.

Temperatures above 33-34°C (91-93°F) are potentially dangerous. A snake that is too warm will usually escape the heat by soaking in its water dish. A snake suffering from overheating will race around its cage with its mouth open. To treat an overheating snake, Rossi and Rossi recommend immersing it in cool running water.

Always, always keep the cage out of direct sunlight. Garter snakes have been killed that way.

Never, ever use “hot rocks” — these plastic rock heaters that are placed inside a cage. They may be dangerous to the snake and are of limited utility: the air needs to be warm, and a cold snake wrapping around a warm rock heater may burn itself.

The jury is out as to whether garter snakes need full-spectrum lighting: some keepers think it isn’t needed, others believe it may help.

Housing more than one snake in a cage
You shouldn't house two or more adults because they might cannabalize each other
But it's fine with the baby's because they seem to do better collectively.

Step 2: Feeding

The types foods you can feed your garter can vary from fish to worms. Types of foods safe for snakes are: feeder guppy's, feeder platys, and worms* you can buy fish at Petco and other pet stores but worms you can catch for free in you backyard or purchase them at garden shops but you have to be carful with either food because fish can have disease and when you snake eats the fish it can get sick but with worms you have to be careful to because garden shops usually sell red wiggler's witch are poison to snakes to see what they look at this steps title picture.
You can feed them pinky mice dead or alive when there older.