Love the silly vibes of this. Seeing the flowers holding a gun gave me a good giggle.
The base gameplay loop is definitely there. To bring it to the next level you'll probably have to add some game balancing (it's too easy at the moment), more enemies, more upgrades, less fertiliser, etc.
I think some silly music at the start would be fun too, to highlight the comedic vibe and then after some time the music becomes more serious and exciting as the player realises this is actually an intense battle between Flower and Fire.