Here is the full list of all 11 Cloud Gardens achievements.
Grow 10000 plants in total
Grow 120 plants in a single Overworld scene
Place 30 gnomes in one scene
Complete the credits scene
Complete every scene on the Overworld
Plant one of each seed in a single scene
Finish the Rooftops Chapter
Use all of the toys in one level
Go to the the Overworld after completing the first chapter
Build a very tall contraption
Unlock a new type of seed