So, I know the basics of the agriculture system, but I have a few questions:
-Do you just have to wait around for mutations to get the different plants (red wheat, ferru, etc)? Is there nothing you can do to influence it at all?
-What's the whole seed drop system about? Most of the time, when I right-click a plant, I don't get any seed drops. How do you maximize your seed drops?
Try Left clicking for seeds 
When I started out i was anxious for mutations as well. It does take a while for them to show up. It may have been coincidence, but it seemed like crossbreeds happened faster for me when I left the two plants I was breeding at the highest level of maturity.
Don't forget to water and fertilize!
that is not coincidence. you can crossbreed only fully grown plants.
That is false you can breed at any maturity its just easier when they're older. I've had a new plant pop up while in the middle of me changing out two seeds the moment I planted one and went to the other.
