Most Earth Ships have areas for gardening and sustainability so that at least some of the food for the household comes directly from inside the house itself! One I saw even had a pool with sustainably reproducing fish in it, so the family could eat fish from their pool and as long as they didn't over-fish, they would repopulate themselves! That is so powerful to me, because it is true freedom and independence!
Earth-sheltered homes can be tailored to a wide range of climates and a variety of types of building sites – even flat ones. Combined with passive solar design, an earth-sheltered home can save tens of thousands of dollars in fuel bills over a lifetime.