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