Growers in colder climates with shorter growing seasons are always trying to cheat the system a bit and extend the growing system. Traditional greenhouses help with this, as does starting seeds off in trays and pots indoors, but both of these methods only allow you to extend the season by a month or two.
An underground greenhouse or ‘walipini’ (an Aymara Indian word for a “place of warmth”) can allow you to grow all year round in most locations. The reason for this is two-fold – firstly, when you dig down four feet into the ground, in most places the temperature stays between 50 and 60 degrees F. On top of this you are capturing and storing the daytime heat, due to the greenhouse being insulated by the warm soil.
Due to the constant temperature below four feet underground, the walipini needs much less energy from the sun to maintain the temperature needed to grow crops, which allows you to grow lots of things all year round.
If you are interested to know more, or you would like to have a go at building your own walipini, the Benson Institute has created and provided a free PDF document, which contains all the information and plans needed to build your own underground greenhouse.