Thank you, I'm glad you liked our game :)
The breeding is unfortunately broken due to a bug in this version of the game. The buttons for plants that haven't been unlocked yet are disabled, but the difference in button style is so subtle it's barely noticeable, we unfortunately didn't have time to change that before we submitted our game. The breeding system is definitely something we are working on improving.
The snail really is unbeatable in this version of the game, we didn't have enough time to really balance things well.
It also spawns earlier than intended because I mindlessly rounded the number of enemies that spawn per type, instad of using floor, causing the snail to spawn when your garden is worth half as much as it should be.