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