So an extra funny idea (IMO) for new version of FG.:)
How about having some garden-limited plants? For example, only certain gardens(like gardens with odd/even numbers) can raise one of the specific variant of plant. To complete the collection, the only way is to trade with/gift between other users.
And to be more detailed...let's say there's a plant having 3 variants A,B and C. Some can raise only A, some can raise B and the rest raise C. Players need to change theirs with each other to get all 3 variants.
I was chatting with Myon and she brought up this thought to me.( We were talking about variants of wild strawberry...)
P.S. Maybe there's another name for this kind of things? Garden-bounded?