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.
Defeat 50 Snowcaps.
Vanquish the Grove's Clutch.
Defeat 50 Glomps.
Upgrade a jar to Grade 4.
Defeat 50 Hayrots.
Obtain the Silversword
Arrive in Winter Glade.
Defeat 50 Shelled Oozes.
Obtain the Flute.
Roll 100 times.
Defeat the Rotberg once.
Take the Lift to Autumn Town
Upgrade a tool to Grade 4.
Defeat 50 Acorns.
Complete Goldie's Favor.
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.