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