Flower Pot

Flower Pots let you plant on the roof, like a Lily-Pad fir roof. But the Lily-Pad can only be planted in water.

Strategy
A flower pot, by itself, can get hit by peas from Zombotany Zombies (it also makes any and all plants on it, even the unarmed Potato Mine, Puff-Shroom and Sun-shroom get hit by the peas as well)

Trivia

 * You can plant a flower pot on a lilypad, but not the other way around.

On roof levels, there are always at least 3 columns of these to start.