I have a checkered garter, Zoomer. I've done a lot of research on their care, and with my experience, this is what I've found.
Environment:
The same set up as a corn except - they need a larger water area. Garters are actually semi-water snakes, and need a large water area for swimming, and hanging out. The really big snake bowls, or a dog dish, or even (for an adult) a "shoebox" in their viv, (or some such set up) would be good. Of course it doesn't have to be TOO big. I like to use a third of their tank, for example. The heat is about the same as a corns, to a little less than a corns. Aspen is good to use. They also like a little tree or branch to climb and hang out in.
Food:
Some food, which is even suggested by some idiots, is toxic to use. Never use red wiggler worms, or feeder goldfish. The worms will kill them, and the goldfish create a thiaminase (sp?) problem. They are not insectivores, so no crickets. You can feed them nightcrawlers cut to size (rinsed), guppies (they chase them in the water), a cut strip of raw ocean perch (rinsed!), and some garters (especially checkereds) will eat pinkies. Some won't, but you can try scenting with tuna juice to try and get them used to it. Zoomer eats almost exclusively pinkies now, which is a good food source. Do not use anything from the garden/yard where there are toxins, etc. Zoomer won't eat in a feeding tub, I think it is because of his nervous nature. His water side has no substrate (papertowels under the bowl and covering the area), so I use tongs and feed him on that side.
Handling:
Garters are flighty, fast, and don't really like to be held. They are not bitey by nature. They are diurnal, so they are fun to watch during the day. Their scales are different than corns, and even kings. The scales are much thicker, and probably feel like a rattlesnake, though I wouldn't know. :grin01:
If you need anymore advice, just ask.