How do you beat survial Day (Hard)?

Warning: you must have all the plants l asked first are you cheaters or not? Okay if you are not cheater you have to set your plants effectively, first
L tell you to pick sunflower of course, then peashooter,repeater,blover,squash then it's up to you for left slot. Start the game, place 1 sunflower in all lanes if you can, make 2 sunflower in every lanes then use peashooter first, as time go by try use repeater and other thing you have, then if you see a baloon zombie just use blover, l hope you have tall-nuts too plant them in front to make defenses. Hope this help you good luck!

It's simple. Your setup should be like this:
Twin sunflower,cactus,repeater,stumpfire,tall-nut

Start with sunflowers and peashooters; start to replace them with twins and repeaters. If you want put chompers behind tall-nuts and gattling peas on repeaters.

Hope you've unlocked all the plants I mentioned!