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