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