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