rec.gardens isn't a listserv, and it isn't a mailinglist. It's just a
newsgroup, and you get it by typing "rn rec.gardens" if you're on a
UNIX machine that's on the Internet, which I think you are. (Your
login ends in ".edu" rather than ".BITNET".)
Unfortunately, I think you will find that newsgroups have a much lower
signal:noise ratio than mailinglists. I almost never even try to read
news any more; gave it up about 5 years ago.
Cheers!
jon