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