[greyhawk]

Well, a similar idea would be to find a gravid female. Just look for a big fat garter in maybe june or july and theres a chance it might pop some babies out in idk, august, september, somewhere around there. I don't know much about breeding and brumation in captivity, but I do know I've seen garters mating in the fall, usually after a cool rainy period. So I think they can breed whenever they are up to it, but its probably a safer bet to try and cool them down first.