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