That was awesome -- I really wish it was a full game! I would love to play it longer, find new plants from "exploring the world" etc. Maybe different regions would be friendly to different plants, and certain plants could be hardier than others -- so there would be more strategy in the crossbreeding, as you tried to get a profitable plant that also grew well in many garden plots.
I agree with the suggestion that hovering over cards should show the plant's stats, and I found the card-merging a bit finicky at times: sometimes I merged cards by accident, other times I tried to merge cards and they missed each other. Maybe that's just because I'm using a touchpad.
Another suggestion: our "research" panel could include a family tree of different crossbreeds. I made my own in Paint.net, which was doable because there were only three parent species -- but it would get a bit overwhelming with more than that. Also, I wished quite a few times that I could rearrange the cards in my hand (to sort them by type and level).
I'll definitely be playing again as-is, though; it was very relaxing.