Creepin' It Real
Polymer clay artists love to make plants, and there are numerous how-to books on the subject. Most of the time they're making 1:12 scale miniatures so the quantities of components would need to be massively upsized but the fundamental techniques should be the same. I have some old books kicking around that I'll need to consult. This one on Amazon looks particularly promising. I haven't been to Polymer Clay Central in years but I'm sure they are the same friendly, welcoming bunch they always were. They would definitely be your go-to source for where to purchase clay in one pound sizes, molding compounds, as well as general (and advanced) information about using the medium.