I'm working on a project and need information on plants (hardiness, soil reqs, etc) that can be listed (under license or commons), and I'm willing to pay for the info if I absolutely have to - but I was hoping for a way to source the information while citing the author. The problem is that it will be a large scale project, and for profit, so I may need to license it.

Is there any source someone can recommend to me in which I can accomplish this? The USDA site has very little info available on plants, so they're not an ideal source. Any info would be very helpful. Thanks GW.