Here's a couple of thoughts-
I would rather not recreate something here that can be done much better.
We can do far more, it's just a matter of dreaming it up!
Take the who's growing this plant in the database idea.
In theory, it sounds pretty good. However, practice makes it a bit (ok- a lot) clunky and really, almost useless.
For example- if a member posts that they are growing SuchNSuch zinnia in their location. Really, they can grow ALL zinnias in their location, but they system only allows for one click at a time. Not very helpful if I'm searching in a generalized way for a yellow annual that grows about a foot tall for my area.
Also, popular plants have lists pages long of people who says that it grows for them. Looking for my area in a list so long that I have to scroll isn't very efficient.
There has to be better ways to give people the information that they really want.