I am posting this because I am very interested in finding this out!
I have noticed when I search that there are not many threads about growth rates and "adult" sizes of the different Garters. I thought, this would be a good way to start off here is to ask:

How fast does your snake grow, and what is the generally accepted "adult" size of that subspecies?

Mine is a Valley Garter (T.s. fitchi) and I am terribly curious of how fast she will grow and how big she can possibly get!
I am sure there are others that would love to know about the other sub-species!

Thanks ahead of time!
Pete