Greenhouse

Summary

 * Greenhouse is unlocked after reaching Area 13, and costs 4 moonstones to build
 * Tree seeds can drop from breaking blocks (you only have to find 1)
 * Seeds can be bought inside the greenhouse shop; they are bought instantly and sell for the same price they're bought at, so this is the easiest way to give someone in your guild coins.
 * To grow the plant you need water from the Water Collector
 * The Greenhouse is a great way to get extra coins, or coal later in the game