Start out by placing two columns of Sunflowers in the back, but do not plant Sunflowers on the second column in the second and fourth rows. Plant Umbrella Leaves there instead.
Then, plant Melon-pults in the third columns before the first wave comes. Use Squashes and Potato Mines for rows without Melon-pults. Do not use Melon-pults when you only have one column of Sunflowers, you will run out of sun extremely quickly, and strong zombies may appear.
In the fourth column, plant Umbrella Leaves in the second and fourth rows, and plant Snow Peas in the fifth column.
Then, plant Melon-pults in the first, third, and fifth lanes in the fourth column.
Finally, remove the Sunflowers in the second and fourth rows in the first column, and replace them with Melon-pults.
Note: You should have purchased Roof Cleaner before playing this level.