Sunflower- Needed as an essential sun producing plant.
Twin Sunflower- A double upgrade to Sunflower.
Pumpkin- To protect the plants and Tall-Nuts.
Tall-Nut- Used to protect Gatling Peas(or Repeaters or Peashooters) and Twin Sunflowers(or Sunflowers).
Gatling Pea- HUGE help for a row of Repeaters with a Torchwood.
Repeater- If enough sun, replace Peashooters with these.
Peashooter- Put as a basic line of defense in early rounds.
Torchwood- To ignite peas passing through to become fireballs.
1. Place 2 columns of Sunflowers and fill the 3rd and 4th columns with Peashooters.
2. Once received enough sun, upgrade the Sunflowers into Twin Sunflowers.
3. Add Peashooters on the 5th column and fill the 6th column with Torchwoods.
4. On the 7th column put some Tall-Nuts.
5. Protect the Tall-Nuts with Pumpkins.
6. Switch all the Peashooters to Repeaters.
7. Upgrade all the Repeaters to Gatling Peas.
8. Watch as those zombies BURN IN ASH!!
If you want to apply extra protection, fill the 8th and 9th column with Spikeweeds than upgrade them to Spikerocks.
There are many strategies out there that are very effective when it comes to Survival Mode like filling the 1st and 4th columns with Gloom-Shrooms and cover all the tiles with Spikerocks, but these are just examples.