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.
Defeat 50 Glomps.
Defeat 50 Snowcaps.
Defeat 50 Hayrots.
Vanquish the Grove's Clutch.
Upgrade a tool to Grade 4.
Defeat 50 Shelled Oozes.
Complete Goldie's Favor.
Obtain the Silversword
Arrive in Winter Glade.
Obtain the Flute.
Defeat 50 Acorns.
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.
Roll 100 times.
Reduce the Rot Dummy to rubble.
Wake up in Spring Hamlet.