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.
Obtain the Silversword
Arrive in Winter Glade.
Obtain the Flute.
Defeat the Rotberg once.
Take the Lift to Autumn Town
Defeat the Octopihi once.
Reach the Summer Bar
Defeat 150 Enemies.
Defeat the Bookworm once.
Roll 100 times.
Reduce the Rot Dummy to rubble.
Wake up in Spring Hamlet.
Defeat 50 Acorns.
Defeat 50 Shelled Oozes.
Defeat 50 Hayrots.
Defeat 50 Snowcaps.
Defeat 50 Glomps.
Upgrade a tool to Grade 4.
Upgrade a jar to Grade 4.
Complete Goldie's Favor.