Plants vs Zombies - Zen Garden

I’m playing on my iPhone and am starting to get aggravated that after months of trying, I can’t seem to complete my zen garden. I think I’m missing about 8 plants. I buy one from Crazy Dave every day, I keep my chocolate at 10 as I know some people think that increases dropped plants, but I still just keep getting the same plants over and over. I’ve heard you can mess with date and time to get new plants from Dave faster, but I don’t think I can do that on my iPhone. Any tips for getting my missing plants?