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