Dude, there's so many places. We
do have a few avid horticulturists around here, but they tend to keep their grow-discussion on the downlow on BL and I think they keep that kind of talk to other forums. Personally, I don't know jack shit about most of the grow process. I can germinate, get shit in the ground and let nature take it's course but that's about it (I've got a greenthumb for other plants, though, and I really want to get my own place and learn how to produce some really decent product myself too.) Site-wise, though? Fucking plenty:
http://forum.grasscity.com/medical-marijuana-cultivation/
http://www.rollitup.org/
http://www.greenmanspage.com/guides.html
Those first two are active forums with a wealth of information already present. They're pretty friendly, though-- moreso than we can be around here, that's for sure.
The last one, greensmanpage, is mainly a bunch of guides (and I mean a fucking
BUNCH.) I don't think they have a forum but it's possible.
There's literally hundreds of others but these three seem to be pretty well-encompassing and the most active with, to my knowledge, the most experienced growers participating in the discussions. Like I said, though, we've got people that really know their shit on this website and they might just come out of hiding to really help ya out.
You've also got shroomery.org but I feel like they were shut down a few years ago... might be confusing them with overgrow, though... eh, idk, like I said, dude, there's so many places to learn this stuff. If you check the Directory thread at the top of this forum (Cannabis Discussion) you'll probably even find a link to a pretty decent set of grow threads we've got archived around here
