I'm playing Plants vs. Zombies on the iPhone and one of the achievements is "Flower Power: Keep 10 Twin Sunflowers Alive in a Single Level". I've tried on many different levels - standard, water, fog, rooftop - but the level doesn't seem to last long enough for me to even plant 10, let alone keep them alive. The cooldown for twin sunflowers is just too long! So what am I missing? What's a good way to get this achievement?
The key is that speed of zombie spawning is somewhat controlled by how fast you kill them, so try to make it as slow as possible. Potato mines are great early on. Snow peas are also good at doing slow damage. And of course you can just throw up walls for them to slowly eat through. Buy yourself enough time and you should have no problem getting enough sunflowers going.