Fun game. The balance between percent and flat upgrades makes for some interesting strategy options. The power spike around opponent 10-12 seems to be too much to handle though. Opponents go from doing ~5 damage a hit to 10+ with no defense.
Once you get the sprinkler, go to the top of the screen and click repeatedly, not holding down. It will draw all the creatures to you and allow your grass to heal while draining your torque a lot more slowly.