Pool's Closed

Strategy
An easy way to do this achievement is to start the first pool level (the icon should look have a Ducky Tube Zombie on it). When picking your plants, you should pick the following:


 * Sunflower
 * Threepeater
 * Cherry Bomb
 * Any other plants you think might help, such as Snow Pea, Potato Mine, and Squash.

As the achievement states, you cannot use water plants. This includes the Lily Pad, so the pool cannot be planted in. The best way to play this level, and have six Sunflowers, is to arrange them in an L shape: 2 sunflowers in the first row, 1 in the second, nothing in the third and fourth rows, 1 sunflower in the fifth row, and 2 sunflowers in the sixth row. This way, you will have a good amount of Sun energy. You should focus on planting the Threepeaters in the 2nd and 5th rows; This way, you can damage the Ducky Zombies that swim down the pool. If zombies are coming too close to the edge of the pool, wait for them to hit a Pool Cleaner, or plant a Cherry Bomb in the row next to them (its area of effect attack will damage zombies in the pool). If zombies on land are getting too close, focus on them by planting Pea Shooter-type plants, or defensive plants like mines.