Theres a trick to do this without the stupid space bar glitch.
What you do is use the green tower, and place is directly and the end of an aisle, and the seeds that are fired will instantly hit the enemies without going thru the air, this works with alll towers, but the green tower has best damage-cost ratio.
Only problem ive come across in this game is the 2 middle trees, as a guardian if u spec down them, and u go against the rockstar u cant actually beat him because of his iron skin/supression combo, actually enabling him to regenerate health without healing, because the Iron skin increases his healht by about 150, then decreases it by 40-50, which is pretty stupid.
 "Epic War 3"){kind=icon}
 "Multitask"){kind=icon}
 "Death vs. Monstars"){kind=icon}
 "Hedgehog Launch 2"){kind=icon}
 "Music Catch 2"){kind=icon}
 "Demolition City"){kind=icon}
 "Epic War 2"){kind=icon}
 "Drop Dead: Final Cut"){kind=icon}
 "Kingdom of The Wind"){kind=icon}
 "Tower Defence"){kind=icon}
 "Sonny"){kind=icon}