Today has been opened an option to unlock rows of clouds through a new 5-step-SkillTree Rune

The amount of clouds per row, and the "effects" will be added to the FAQ soon.
Here is the basic info for each row of clouds:

• Stage 1:
  cost: 20 stars
  3x small clouds, 2x medium clouds, 1x large cloud
  Effect: 5 pheromones
  Cooldown time: 30 hours
• Stage 2:
  cost: 35 stars
  3x small clouds, 2x medium clouds, 1x large cloud
  Effect: 10 salt
  Cooldown time: 30 hours
• Stage 3:
  cost: 50 stars
  3x small clouds, 2x medium clouds, 1x large cloud
  Effect: 10 sugar
  Cooldown time: 30 hours
• Stage 4:
  cost: 65 stars
  3x small clouds, 2x medium clouds, 1x large cloud
  Effect: 1 Albino Bat
  Cooldown time: 30 hours
• Stage 5:
  cost: 80 stars
  3x small clouds, 2x medium clouds, 1x large cloud
  Effect: 1 Brown Pig
  Cooldown time: 30 hours

Source: Official Farmerama Forums.