Plant two columns of Sunflowers while planting Potato Mines to kill the zombies at the start of the level. Then, start planting at least two columns of Cabbage-pults.
After, plant extra Flower Pots and create a column of Wall-nuts.
Plant Snow Peas on the fifth column so they can shoot over the roof.
If necessary, plant an extra Flower Pot and an instant-kill on it to kill extra zombies.
Plant Sunflowers in the first column, then add any Cabbage-pults to where ever the first zombie is. Do the same until you have the second column only Cabbage-pults.
Place Chompers on the third and Tall-nuts on the fourth (any order will do, such as placing one Tall-nut, then one Chomper, etc.).
If necessary, use place Flower Pots to place the instant kill plant to kill any zombies that happen to get dangerously close.
Place two Sunflowers in the first column, then put a Cabbage-pult in the lane that the first zombie is coming and the third column. Keep repeating this process until the first row is full with Sunflowers and the third row is full with Cabbage-pults.
Now start placing Sunflowers in the second row and Cabbage-pults in the fourth.