So I'm pretty sure many people are unhappy with the plant fertilizers because they can only be used once, so what if we also added, for example, sprays? (or something else, I'm open for suggestions lol)

Sprays could be used on a full grown plant and they would pretty much do the same thing as fertilizers but would be slightly less effective to avoid abusing the feature.

Examples:
- faster product growth spray - next harvest comes a few hours/one day sooner
- +1 product spray - gives an additional plant product when we are able to harvest

I also suggest making them harder to find than fertilizers.