Treasure boxes are received by giving care. You do not have to place treasure boxes in your crops to give them to friends, they are automatically and randomly dropped by the game.

Treasure boxes

Treasure box tab in inventory menu showing standard, rare, and premium treasure boxes.

Standard treasure boxes cost one gold key to open.

Rare treasure boxes cost two gold keys to open.

Premium treasure boxes cost ten gold keys to open.

By pressing the middle bottom button with a clipboard and treasure box, you can see a listing of what's available in each type of treasure chest.

Gold keys and premium treasure boxes can be bought from the stars tab of the Shop menu.