Enlightened

Strategy
This achievement is hard and very luck-based, as you need to collect all 39 plants in the Zen Garden (excluding the Flower Pot, Imitater, and Upgrade Plants), and Zen Garden plants dropped by zombies are rare. Try to repeat Adventure Mode as much as you can. Another way to get the achievement is to buy Marigolds from Crazy Dave's shop and use the Zen Garden Editor until you have all the plants.

Tips

 * Play levels with a high zombie density so that more presents can be dropped.
 * Keep 10 chocolate, so that zombies can't drop chocolate.
 * Playing Survival: Endless, I, Zombie Endless and Dr. Zomboss's Revenge will drop every kind of present you need for this achievement.
 * Every 10 levels of Vasebreaker Endless and every 3 levels of I, Zombie Endless will drop a money bag, chocolate, or present. Having 10x chocolate will also lessen the chance of chocolate dropping from these.
 * Another easy way to get all the plants is by manually setting the time on your device forward by one day at a time. Each time you set it forward you will be able to purchase another present for $7,500 at the shop.

Trivia

 * The fact that the achievement is called "Enlightened" implies that once one has collected all of the plants for the Zen Garden, they will have achieved a form of Zen enlightenment (considered the ultimate goal in Zen teachings).