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