Board Thread:Plants vs. Zombies 2: It's About Time/@comment-24735666-20140724221412/@comment-24275721-20140728140529

Uselessguy wrote: @TheGolldMAN Using this strategy is also effective in most levels in Dark Ages, especially Night 16, 17, 18 and 19. That's why we don't need to buy Plant Foods or using ANY POWER UPS or boosts.

Except Night 19, you need to restart the level sometimes, just keep removing Grave Busters to have tiles for your plants to protect. I don't have Part 2 yet but I will try it once I get it.