Here is the full list of all 21 Plants vs. Zombies GOTY Edition achievements. It takes around 40-50 hours to unlock all of the achievements on Windows.
Complete a nighttime level without planting any Mushrooms.
Grow the Tree of Wisdom to 100 feet
Defeat 2 Gargantuars with Corn Cob missiles in a single level.
Discover the top secret zombie
Get 8000 sun during a single level.
Defeat a normal roof level without using any catapult plants.
Complete a daytime pool level without using pea shooters of any kind.
Complete a daytime level by planting only Mushrooms and Coffee Beans.
Collect all 49 plants
Get to 20 flags in Survival Endless
Enable Mustache Mode
Get the golden sunflower trophy
Beat all 20 mini games.
Bowl over 5 zombies with a single Wall-Nut.
Get to a streak of 10 in I, Zombie Endless
Get to a streak of 15 in Vasebreaker Endless
Complete adventure mode
Hypnotize the lead dancer zombie
Pick up 30 coins in a row on a single level without letting any disappear.
Blow up a zombie using a potato mine
Blow up 10 zombies with a single cherry bomb