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