Very fun game! At the start I really struggled to survive more than 10 seconds but once I'd been playing for a while then it actually got pretty easy which I think is the sign of a fair but challenging game. I think you had a perfect balance of simplicity and interest, with the planting mechanic giving you a goal other than running away.
The only thing I found a bit odd was that the enemies move faster than you which makes it seem impossible to escape them at times. If the enemies moved at the same speed as the player I think it would feel a bit more fair.
Overall though, great job!