The Walipini: A Coldproof Underground Greenhouse

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The Walipini: A Coldproof Underground Greenhouse

Love growing cannabis outdoors but held back by a cold climate? Consider building an underground greenhouse!

Growing cannabis outdoors in the colder regions of the world can be tough. Gardeners are always trying to think of new ways and techniques that will allow them to get the most from their plants, and even grow all year around.

Well, one effective solution, albeit quite extreme, is to build your very own sunken underground greenhouse. Known as a walipini, these sunken greenhouse “pits” were first developed over 20 years ago in the colder mountainous regions of South America in order to allow locals to grow crops all year-round. Unlike traditional greenhouses, which normally consist of expensive metal frames and glass, a walipini utilises the protective and insulating properties of earth, combined with the passive solar energy of the sun to create an environment that would otherwise be impossible.

If you think about a normal greenhouse, although it technically shelters the cannabis within, it is still exposed on all sides to the elements, making it hard to maintain its heat during the winter months. As an underground greenhouse is sunken into the earth, exposure is not an issue, and being surround by think layers of earth on all sides actually allows for the tapping of thermal mass, keeping the pit warm!

Building Your Own

Although a massive sunken pit in your garden may not be discreet, a small, carefully planned one can be. As the core principles behind their construction remain the same no matter the size, a sunken greenhouse can be adapted for any situation; and the great news is they are pretty inexpensive to build, all you need is time and a lot of effort.

You will need:

- Energy, will power and the ability to work hard with your hands

- Clear plastic roof sheeting

- Earth to build with

The basic principle is to dig a rectangle at least 2.5 meters deep (deeper if you want to grow some mammoth strains). The width and length of the rectangle can be anything, and should be large enough to comfortably accommodate however many plants you want to grow (as well as maybe some supplies).

The length of the rectangle (its longest area), should be dug to face the winter sun - facing south in the northern hemisphere, and north if you are in the Sothern hemisphere.

You then need to make a taller packed earth wall at the back length of the rectangle, followed by a smaller packed earth wall at the front. This will create a nice slope for you to put some plastic sheeting on. To get optimal sun penetration, the plastic sheet roofing should be angled at 39 degrees from the taller back wall.

Once this is done, you need to build up the sides of the rectangle into walls, to create a fully enclosed, encapsulated pit.

For more detailed instructions, have a look at the publication of the Benson Agriculture and Food Institute.

Your Very Own Micro-environment

Once you have completed the build, you will have made your very own little pocket of warmth that should be able to support cannabis plants even in the coldest of winters. Thanks to the shelter, sun’s rays, and the thermal mass of the earth, it should take very little energy to actually heat the sunken pit up!

Of course, you will need to take into account such things as ventilation, access, and drainage, but with the core principles in hand, you should be able to plan and build a pit to suit your needs, it just takes a bit of ingenuity and elbow grease! Good luck!