Really helpful feedback! I appreciate it.
I agree, the current build does little to distinguish the flowers apart from each other. My current thinking is that I'll add an upgrade that grants a chance to get a special version of the seed which will add a buff when it's collected. E.g. a special version of the Vine will shoot out to random seeds on the board and instantly collect them. Or a special Sunflower will create additional sunflowers surrounding it.
I will look into adding more meta progression systems as well.
Thank you for the feedback regarding the fertilizer aesthetic.