Here is the full list of all 11 Gnome achievements.
You threw away the gnome.
This wasn't the right ending.
Opened the curtains when something wanted them closed.
You finished the first day taking care of your friends house.
Discovered a mushroom house at the end of the Trial Forest.
Met the garden gnome named Darry.
Was there something in the mirror?
Planted some strange seeds.
Watered some strange seeds with a strange liquid.
Finally planted the plant starts after watering and watching them grow.
Finished Gnome.