Despite the fact that I'm an accomplished gardener (10 skill and omniplant seeds), I still haven't figured how the hell fertilizing works. I've tried fertilizing individual plants with perfect fertilizers, but they still grow with the same speed and yield the same quality produce with the rest of the batch I planted. Help.
I have in no way tested this scientifically, but it seems to me that fertilizing with better items (fish, in my case) might make your plants live longer. I've noticed that plants that have been fertilized with perfect fish seem to live longer than those which are not fertilized, or fertilized with poorer quality fish. I'm openly admitting that it's not something I'm watching with a magnifying glass, so it could be observer error, but I do think this is what I'm seeing...possibly.
Edited to add that I've also seen the quality of plants increase over time, but I don't know if it's because they've been fertilized (most of my long-term plants are) and/or talked to. This has mostly happened with my money trees, but I believe I've also seen my apple trees improve quality.
Also, someone long ago in this thread mentioned that money trees don't drop seeds - I've found that they do - rarely, but they do drop seeds. You just need to keep your eyeballs peeled.