Use the following plant formation with the following items to create a fort:

0: Sunflowers or upgraded flowers
1: A shooter plant
2: Repeater/upgraded
3: Three shooter plant (three lanes)
4: Fire Plant (fire tree that turns bullets to fire balls that pass through it)
5: Cattail
6: Squash (or Wallnut/Tallnut)
7: Small mushrooms
8: Chomper
9: Scardey Shroom
X: Free space

In the morning:

0 1 2 3 4 6 8
0 1 2 3 4 6 8
0 1 2 3 4 6 8
0 1 2 3 4 6 8
0 1 2 3 4 6 8

At night:

0 2 3 4 9 X 7 7 7 6
0 2 3 4 9 X 7 7 7 6
0 2 3 4 9 X 7 7 7 6
0 2 3 4 9 X 7 7 7 6
0 2 3 4 9 X 7 7 7 6