Generally speaking I prefer to not create any forum unless it's going to be highly trafficked and used by a lot of people.
We have forums dedicated to roses, irises, lilies, and daylilies (and others) because there are thousands of cultivars of each, and there's a lot to talk about.
Milkweed is kind of a different kind of plant. There aren't thousands of cultivars and as far as I know there is no breeding work being done or other things to discuss. My concern with creating the forum is that there's not enough to talk about with them, and therefore the forum could become inactive, which looks really bad. There's nothing worse than going into a forum and seeing the most recent post was months ago.
I think it might make more sense to have a forum dedicated to specific plants for butterflies? And milkweed would then be the main topic of that forum?
