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