Build a $300 Underground Greenhouse for Year-Round Gardening

Growers in cold climates often utilize various approaches to extend the growing season or boost their crops, including cold frames, hoop houses, and greenhouses. Greenhouses—typically glazed structures— are often expensive to construct and heat throughout the winter. But, they have their benefits, which is why underground greenhouses can be viable alternatives.

The walipini (an Aymara Indian word for a "place of warmth"), also known as an underground or pit greenhouse, is a much more affordable and effective year-round option than the traditional glass greenhouse. First developed for the cold mountainous regions of South America, the in-ground greenhouse allows growers to maintain a productive garden 365 days a year, even in the coldest climates.

How an Underground Greenhouse Works and How to Build One

An underground greenhouse (walipini) is an intriguing set-up combining the principles of passive solar heating with an earth-sheltered building. But how do you make one? American sustainable agriculture non-profit Benson Institute provides the enlightening manual below on how an underground greenhouse works and how to build one:

The Walipini utilizes nature’s resources to provide a warm, stable, well-lit environment for year-round vegetable production. Locating the growing area 6’ to 8’ underground and capturing and storing daytime solar radiation are the most important principles in building a successful Walipini.

The Walipini, in simplest terms, is a rectangular hole in the ground 6‛ to 8’ deep covered by plastic sheeting. The longest area of the rectangle faces the winter sun – to the north in the Southern Hemisphere and to the south in the Northern Hemisphere. A thick wall of rammed earth at the back of the building and a much lower wall at the front provide the needed angle for the plastic sheet roof. This roof seals the hole, provides an insulating airspace between the two layers of plastic (a sheet on the top and another on the bottom of the roof/poles) and allows the sun's rays to penetrate creating a warm, stable environment for plant growth.

Benson Institute's earth-sheltered greenhouse taps into the earth's thermal mass so much less energy is needed to heat the walipini's interior than an aboveground greenhouse. Of course, there are precautions to take in waterproofing, drainage, and ventilation, while aligning the greenhouse properly to the sun—which the manual covers in detail.

Best of all, according to Benson Institute, its 20'x74' walipini field model in La Paz cost just around $250 to $300 to build, thanks to help from the owners and their neighbors, and the use of cheaper materials like plastic ultraviolet (UV) protective sheeting and PVC piping.

Cheap and effective, an underground greenhouse is a great way for growers to produce food year-round in colder climates.