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