Here is the full list of all 21 Garden Story achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Vanquish the Grove's Clutch.
Upgrade a jar to Grade 4.
Defeat 50 Glomps.
Defeat 50 Snowcaps.
Obtain the Silversword
Arrive in Winter Glade.
Defeat 50 Hayrots.
Complete Goldie's Favor.
Defeat 50 Shelled Oozes.
Obtain the Flute.
Defeat the Rotberg once.
Roll 100 times.
Take the Lift to Autumn Town
Defeat 50 Acorns.
Upgrade a tool to Grade 4.
Defeat the Octopihi once.
Reach the Summer Bar
Defeat the Bookworm once.
Defeat 150 Enemies.
Reduce the Rot Dummy to rubble.
Wake up in Spring Hamlet.