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