The Earth-Sheltered Solar Greenhouse Book: How to Build an Energy Free Year-Round Greenhouse (Anglais) Broché – 6 juin 2007
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Temperature varies from minus 35 to 35 above degrees celcius. A short growing season and expensive to try and heat and cool a traditional greenhouse in these extremes. The underground greenhouse so far has proven to be the perfect answer to these challenges.
Temperature stats: coldest temp: 3 days of -4 for the lows, enough to freeze my tomatoes in the middle of February when it averaged -30 degrees Celcius outside at night. Everything survived the earlier two cold snaps that didn't go below -25. Most other days of the year were between +7 and 23 in the greenhouse. It is very rare that temperature goes outside of this range. All it would take is a small space heater running a few of the very coldest days to go year round in this. I probably won't do that though. I think it is better to start over completely each season.
My greenhouse measures 16 feet long, six wide, 13 tall. The grow bed is 4 feet wide, with a two foot wide by 3 foot deep cold sink. Along the back north wall I have a 300 gallon water wall with 52 vertical hydroponic net pots. I grow peppers, tomatoes, snap peas, carotts, beets, legal herbs, spinach and all kinds of lettuce. I start all of my regular garden plants in it too. The glazing is 54 degrees - a little flat for this far north but still quite effective at getting the sun in durring winter and out when directly overhead in mid-summer. Wax pistons expand in the heat of the day to push open two vents and a small solar fan keeps the air moving.
I spent a few grand on this. Very nice double wall polycarbonate, decent 4x4 and 6x6 posts, 30r insulation on the roof, east and west walls and of course the hydroponics pump, resevoir, net pots and piping was a little over a third of the cost. I dropped a bit of coin on an Aquaponics controller to monitor PH and temperature 24/7 right on my iPhone with real time SMS alerts when temps go above or below certain thresholds. Stats galore! We have our pet rabbit, a flemish giant living in a burrow on the south side of the cold sink. He puts out a little bit of heat and a lot of CO2. His burrow temperature is usually steady at 12 degrees. Its a bit cruel for him only because he has to stare at delicious carrots and beets all the time.
I live right in the middle of the suberbs with stringent building codes and covenants. The thing had to look half decent. Having half of it underground helped in this regard as it doesn't look any more imposing than a small shed on the side of my house.
The first year has been a lot of trial and error but I am certain at this point that my 10 square metres of land this occupies will be more than enough to put a decent salad on our familly's table for three quarters of the year going forward.
Three weeks of after work and weekend digging and seven more of contruction were involved. Lessons learned - wait until the ground thaws before digging it out, have a place to put the dirt from the hole and building codes be damned, I should have made it bigger because it really works!
In Mike's latest book, "The Earth-Sheltered Solar Greenhouse: How to Build an Energy Free Year-round Greenhouse," he explains various experiments that he has made over many decades with digging into the ground to take advantage of the inherent heat retained by the earth. Mike has an inimitable, curmudgeonly and witty style of writing that makes this an enjoyable read.
Gardeners have often made simple "cold frames" to extend the gardening season by surrounding plants with low glazing. This works for awhile, but eventually the cold will get through and the plants will freeze. Mike tried digging a grow hole with glazing over it, and this worked to some extent, but ultimately cold and insufficient light got to his plants.
With Mike's experience living in an underground house he had learned a few things about the way heat and cold behave. He knew that hot air rises and cold air sinks down to the lowest spot available. With this in mind he realized that what the grow hole really needed was a place for that cold air to go so that it didn't freeze the plants. His next experiment was to make a little recessed greenhouse that had a space wide enough to walk in on the south side that was lower than the growing bed. This not only provided a place to stand while working in the greenhouse, but also provided that place for the cold air to reside.
This simple idea is really the basis of Mike's remarkable success in greenhouse gardening. He lives in Idaho, near the Canadian border, where winter gardening is a real challenge, and he claims that with this concept he can keep plants alive year round and extend the growing season many months each year...all without additional energy inputs other than the natural heat from the sun and the earth.
The book goes into much more detail about various ways to accomplish the requirements of his underground greenhouse concept. He discusses ways to provide a framework that can withstand the pressures of the earth on it. Different glazing materials are evaluated. Strategies for retaining more heat in the surrounding ground and for providing sufficient light and ventilation to keep the plants happy are explored.
A surprising area of inquiry is that of companion housing for small critters, such as rabbits, ducks, and chickens, within the greenhouse space. There can be a symbiotic relationship there, where the greenhouse provides a benign habitat, and the animals provide needed fertilizer and carbon dioxide for the plants. They can even eat garden refuse and some insects. Of course all of this has to be carefully managed so that both plants and animals are kept in their places. Mike prefers making a space for rabbits under a walkway in the cold sink, claiming that this is a perfectly natural place for rabbits to thrive; they just need a way to get into the sunlight periodically.
With the companion sheltering for animals and plants, there is the possibility of a system whereby a complete diet of veggies and protein from eggs and meat is possible. This is a survivalist's dream! And all can be arranged within a modest budget and without using fossil fuel inputs.
Mike's book is liberally illustrated with many delightful drawings of plants, insects, and animals, as well as diagrams and photos of his greenhouse concepts. I think anyone with a modicum of carpentry skill could take what is explained in the book and create a solar heated underground greenhouse that would enhance most any homestead.
Having said that, the author seems to be just about the only person around advocating earth-sheltered greenhouses. The concept is simple and I have to wonder why it's not more common. In fact, it's so simple that one only needs to read the article by the author on the Mother Earth News Website. I read that article and found the concept intriguing, so I bought the book, expecting some formal, in-depth research on the subject. All the evidence in the book supporting the concept is from the author's personal experience and vague "recollection". I would like to see some university or professional research on the subject. I am in the market for my first greenhouse, but I'm still undecided after reading this. Take away 1 more star for lack of formal test results.