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