Once you unlock pumpkin bombs

Once you unlock pumpkin bombs use these to clear large quantities of high quality zombies. They will 1 shot ghouls, and take out the others in 2-3 hits. Do not use to kill low call zombies. Remember you can fill every square of the lane. This includes the farthest on to right where the zombies spawn. You can drop a rocknut there to slow the initial spawn down, place strangler vines, etc.
po wow
The warden fight is pretty much the same thing. Build up defences, beat back zombie pushes, then when warden shows up and is hp pool becomes vulnerable go drop pumpkin bombs next to him until he dies.

Which part of the fight are you having trouble with btw?