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