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.
Vanquish the Grove's Clutch.
Upgrade a jar to Grade 4.
Defeat 50 Snowcaps.
Defeat 50 Glomps.
Defeat 50 Shelled Oozes.
Defeat 50 Hayrots.
Complete Goldie's Favor.
Upgrade a tool to Grade 4.
Obtain the Flute.
Roll 100 times.
Obtain the Silversword
Defeat 50 Acorns.
Arrive in Winter Glade.
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.