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.
Reach the Summer Bar
Take the Lift to Autumn Town
Arrive in Winter Glade.
Defeat the Bookworm once.
Defeat the Octopihi once.
Defeat the Rotberg once.
Vanquish the Grove's Clutch.
Defeat 150 Enemies.
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.
Obtain the Flute.
Obtain the Silversword
Complete Goldie's Favor.
Reduce the Rot Dummy to rubble.
Roll 100 times.