Grow only life-fruit (by far the most valuable produce) and garlic to use as fertalizer.
For people who like playing gardeners...
This weekend I found a harvestable that came with UL that is more profitable than life fruit. One of the new coffee beans (think it is called "red berry bean" if I remember it right) that you can buy from the grocery store for $50 each. Perfect versions are worth $200 each, and through the consignment shops can bring much more.
The real kicker is.... these beans are "common" for rarity and grow as fast as tomatoes and apples so far in my playing/testing this weekend. So once you have perfect species going, there really isn't any need to fertilize as they still grow and produce just as fast.
So I think perhaps life fruit might be knocked off the most profitable gardening peg. These beans can be purchased at the grocery store with no need to find the special seeds and see what develops. They can also be planted much earlier on in a gardeners progression through the skill. As they grow faster, it is also easier/quicker to get them to "perfect" versions as well. Would be interested to see if anyone else can duplicate this in their game as I haven't read anyone else talking about it yet. I hope it isn't just some cool glitch that happened in my game.
I also hope it is okay reviving an older thread, but it seems like this thread is right on topic for what I found this weekend. And I wanted to make sure and share the find with others that like playing gardeners.