I was searching the boards and quite shocked to see people saying plants have the advantage. My biggest issue is surviving a zombie rush. For 25 sun(brain?) the vanilla zombie seems too cost efficient, with the only equal cost counter being a potato mine which has a much longer cooldown time. It's so easy to spam these zombies while planting graves. What is a good opening strategy to counter the steady stream of cheap zombies while still being able to plant sunflowers and get some sort of offense going ?
Sounds like you need some squash. Very fast cooldown, pretty cheap, and they don't have to arm themselves like potato mines. Don't be afraid to let the zombies close a little distance either, that means more time to harvest sun. Wait until they're just about to reach your first plant or lawnmower, then drop a squash on 'em. Meanwhile, you've been harvesting sun.
It's all about time, the longer you keep your opponent busy with squash and wallnuts in the early game, the quicker you'll be able to get your real defenses up. I don't even put up any attacking plants until I have at least 3-4 sunflowers out, sometimes even a full row, and I remain undefeated. Granted, I remain unvictorious with the zombie horde, but what can I say, I don't have a taste for brains.
Remember squashes stop anything that walks in one hit, except gargantuars, they take two. So if you see an opportunity in the early game to plant a peashooter for 100 sun, plant a sunflower and a squash or wallnut instead.
I believe squash is also on a fairly slow cooldown, and it's cost is 50 more sun then the zombie it kills. The pepper is 100 more and the cherry is 125 more sun then a vanilla zombie. Plants are forced to spend all their sun to fight off these super cheap zombies while zombies mass produce graves and constantly attack.
I use squash and mines as much as I can, but I cant stop a well planned attack from getting through somewhere. Once you start having sunflowers get eaten it's almost impossible to recover.