Imagine with me, if you will, a scene in Idaho, a beautiful mountain valley, part of the Snake River channel.
It’s the dead of winter. The snow is almost 4′ deep on the ground. The river has been completely frozen over for more than a month because the daytime temperatures haven’t made it above -10 F for a couple of weeks and the nights have been hovering between -30 F & -40 F (yes, that’s 10 below zero Fahrenheit and 30-40 below zero Fahrenheit), unusually cold even for this area.
In the midst of this deep-freeze you stumble across a tropical oasis, a place that is delightfully warm and humid using only the heat of the sun. No furnace heats or dries the air here! The fragrance in the air coming from the beautiful flowers – some hanging down from overhead and others growing happily in their beds, all completely oblivious to the snow and the temperatures around them – is almost intoxicating. There are also lots of beautiful vegetables growing – broccoli, cabbage, carrots, peppers, tomatoes, and others.
“IMPOSSIBLE!!!!” you say.
But, no, it isn’t. You have just imagined yourself walking with me back through the mists of not-too-distant time when I actually had this experience myself.
In the midst of this bitter cold, I had been invited to visit the inside of a friend’s walipini. Walipini is an Aymaran Indian word from South America that basically means “warm place.”
You may have guessed by now, or gone to look it up, but just in case you’re still wondering, a walipini is essentially an earth-sheltered greenhouse. The concept has been around and utilized by various societies for centuries but fell into disuse in most areas with the advancement of technology. It was revived in the late 60’s by the Benson Institute as a way poor people in the Andes could provide more vegetables for their families to eat and to sell. Since then, the concept has been elaborated on with modern earth-sheltered greenhouses making use of some fairly extensive buried pipe systems, fans to circulate air through the pipes and greenhouses, and electricity to run the fans. A rather expensive elaboration, at least from my perspective.
A traditional walipini has earthen walls, sloped so the bottom is narrower than the top, no heat source other than the earth and sun, and the vegetables are grown directly on the earthen floor.
My husband doesn’t trust the earthen walls to hold safely in our sandy bouldery soil and my body no longer tolerates sitting or kneeling on the ground to garden so we’ve made some modifications. Here’s an account of our modified walipini build, and some of the results in both words and pictures.
The first step was dig out a hole 2 ½ -3 feet below the frost line, and sufficiently large to allow us to work around all sides of the structure as we were building it.
Then came framing the walls, with a little “help” from a 4-footed friend who had to keep a close eye on everything. Yes, we used framed walls. I told you my husband didn’t trust our “dirt” to hold.
3 of the 4 walls framed it was time to begin putting the puzzle pieces together. FWIW, you can’t calculate the size by counting the studs because my husband wanted them significantly closer together than normal to help withstand the pressure of the dirt once we back-filled the hole.
Once the walls and rafters were in place, we then used 2×6 lumber to side the whole thing, sealed the wood inside and out, painted it, covered the walls that would have dirt contact with 6 mil black plastic, and back-filled the hole. We also added a vestibule to help moderate the cold winter – which was fortunate since having solid wood walls insulated it from the stabilizing temperature of the earth so it gets colder than the one in Idaho with earth walls – quite a bit colder, in fact.
We used clear corrugated plastic roofing panels in the hope that they will prove more durable to the constant wind and frequent hail this area is subject too, as well as providing a slippery slope for the snow to slide off. This plastic also blocks much of the harmful UV while letting in the UV the plants need as well the warming infrared rays. The next steps were to build retaining walls on both sides of the entrance from boulders that were dug out of the hole and build the cement block raised beds inside for the actual garden area.
I used a modification of Hugelkulture to fill the beds, starting with a base of about 10-12″ of scrap lumber to help hold moisture and draw plant roots deep. This was then topped with 3-4″ of a mix of hay, steer, and chicken manure for plant nutrients and to provide some heat for the soil as the hay and manure decompose. Then came about 10-12″ of potting soil that I mixed up on site. Each layer was well watered before the next layer went on.
The final result? I grew all of the tomatoes and squash we could use last summer and had extra to share with neighbors – who all lost their gardens due to late frost the first week in July. I had to use shade cloth in addition to leaving the door and window open to keep from cooking my veggies where they grew! I’ve added 3 more windows high on the north side with automatic vent openers that are controlled solely by the heat in the hope that they will keep the walipini cooler this summer and allow me to grow more than tomatoes and squash.
This past winter, I found that with the insulation of the wooden walls, the walipini initially only gave me about 20 degrees of protection from the outside temperature. After adding a layer of ordinary bubble wrap to the underneath side of the rafters, I have about a 30 degree protection factor. That’s not enough to grow tomatoes through the winter like my friend in Idaho, but it’s enough to allow for growing cold tolerant/cold loving veggies (especially salad greens) through the winter. In fact, although we’re still getting nighttime temperatures in the single digits and low teens, I have tomatoes, squashes, peppers, broccoli, kale, beans, peas, and a couple of types of leaf lettuce growing in there right now, and all very happy.