Jerome Osentowski is the director and founder of the Central Rocky Mountain Institute of Permaculture. He showed how to design and build a successful greenhouse project in a forest garden greenhouse (Chelsea Green Press, 2015). Learn how to use passive and active solar heating strategies to create tropical or Mediterranean climates even at high altitudes or cold climates. The following excerpt is from Chapter 2, "Expanding Possibilities by Extending the Season".
In the next part, we will describe the bell-shaped house, the hoop house, the dome, the greenhouse connected to the drain, and the four-season greenhouse. By combining solar energy collection, thermal mass, and insulation to capture and store energy, we can effectively grow a wider variety of plants, even in snowy countries.
We are also learning how the underground soil balances temperature fluctuations in cold and hot climates and provides a supportive growth environment for the edible plants we want to eat. At the time of writing, we are designing a climate battery for a greenhouse in the hot southwest desert. The battery uses the same opposite principle. The greenhouse will draw in daytime ventilation air from the shady orchard area through colder underground pipes before entering the greenhouse, and add water mist evaporators on really hot days to help maintain moderate internal temperature and humidity levels. For a future that depends on renewable energy and limited supply, we need to save as much energy as possible. Growing a wide variety of food crops locally will save transportation energy, preserve resources in the communities where they are produced, and help create unique regional cuisine and artisan cultures.
The simplest form of crop protection is a bell-shaped cover or fabric-covered hoop erected on a plant bed. The simplest bell-shaped cover is just a floating row cover, a porous non-woven fabric, spread on a seedling area and fixed to the edge with rocks or tent stakes. Sunlight passes through the white fabric to nourish the plants, while heat builds up in the soil, keeping them warm at night. This can even provide 4 degrees of frost protection (when outdoors at 29 degrees, the plants in the bell-shaped cover will remain at about 33 degrees). When the seedlings are young, the fabric can be supported by sticks in the soil. Since the mulch is very light, the plants will lift them up as they mature and unfold. Using thick iron wire or thin plastic tubes, you can make a "hoop" bell-shaped cover to support the fabric above the seedlings and provide them with plenty of sunlight and space for growth.
When the danger of frost has passed and your plants are ready to receive direct sunlight, you can remove the fabric during the day and tuck it in at night. Eventually, you can also turn it off at night until the danger of frost in early autumn comes again. In the Rocky Mountains, we can usually use a bell to protect zucchini and even melons from freezing until October. This allows us to extend the normal growing season of three to four months to five to six months.
These structures are like bell jars, but you can walk under them. They are often used in bell ornaments for another layer of protection. In our Rocky Mountain climate, this will postpone the growing season to seven or eight months, or even twelve months in the case of climate batteries and winter planting of hardy vegetables. Using this combination, sunny areas in USDA 6 and warmer regions will be able to grow year-round. In warmer outdoor areas, hoop houses can support a wider variety of crops in winter.
There are many examples of hoop houses, also called "high tunnels", which you can buy as a kit and build your own. The "Rolling Thunder" greenhouse, manufactured by Rimol Greenhouse Systems in New Hampshire, is a high tunnel inspired and favored by Eliot Coleman of Four Seasons Farm in Maine because it rolls on the track, allowing him to start crops under the structure and move first When the batch of crops is ready to grow outdoors, circle the house to the next space, and then start again with another batch of crops under the mulch. The Rolling Thunder greenhouse does not need to propagate plants in the greenhouse and move the plants outdoors, but can easily move the structure.
Most hoop houses use natural ventilation by providing roll-up sidewall covers, but some of them have vents at the top where heat collects. If you use a structure without top vents, it will be cheaper to purchase the structure, but you may need to install a large-capacity fan to keep the hoop house cool during the hottest months of summer. You can also use shading cloths and other light-scattering coverings to reduce the increase in solar heat in summer.
The hoop house can be equipped with double inflatable polyethylene greenhouse film on the frame to provide additional insulation value in cold climates. This method involves stretching two layers of plastic film on the hoop frame, sealing all edges of the two layers to the frame with continuous clips, and installing a fan to inflate the air space between the film layers. The still air between the layers increases the insulation value of the cover. You can also cover the roof of the hoop house with rigid polycarbonate panels. These are more expensive, but they have a longer service life and can provide better insulation values than thin films. Even on hoop houses covered with double inflatable polyethylene, the end walls are often finished with polycarbonate panels, because these flat, rigid surfaces are easier to install swing or sliding doors than film. You can easily mix dual inflatable polyethylene membrane roof coverings and rigid polycarbonate panel end walls on the same structure.
A farmer who has succeeded in a longer growing season may want to buy another hoop house, but soon he will discover one of the shortcomings of simple hoop houses: they cannot be connected side by side to form a large greenhouse like a gutter connection. Can. In the snow country, the hoop house and the high tunnel must be separated far enough so that when snow falls from the roof, it can gather between them. The design of light greenhouse structures must be able to snow, otherwise they may collapse. And this snow must go somewhere by himself. Even if they can support weight, simple hoop houses have no gutter connection that can collect the melted snow.
The result is that the grower can only enter each hoop house from one end. Multiple structures can be connected end to end, but this will result in a very long working path. Even if it is separated horizontally, the construction of the hoop house makes it more like a tunnel than a large sunny warehouse. We dream of establishing a hybrid system between the economy of the hoop house and the flexibility and water collection capacity of the greenhouse system connected by the drainage ditch.
Despite these restrictions, there are serious four-season farmers, such as Eliot Coleman and Barbara Damrosch in Maine, who grow beautiful agricultural products and flowers throughout the year, movable high tunnels, and supplemented by row covers.
Buckminster Fuller invented the geodesic dome, which is a very effective form from the point of view of energy saving and structural performance. The dome relies on triangular and spherical geometry to create a shell that can support heavy snow loads with much less material than traditional linear structures. The spherical shape also has the advantage of enclosing the largest space volume with the smallest surface area, making the dome the most natural and energy-saving shape. This combination of structure and energy-saving efficiency makes the geodesic dome an ideal greenhouse.
In the 1980s, at a research institute named Windstar Land Conservancy in western Colorado, Buckminster Fuller designed a greenhouse dome, which he called a biological dome structure. The Windstar biological dome is 50 feet in diameter. In addition to the ground area, there are two attics for growing food and two large water tanks for fish farming, fertilizer storage and heat storage. That greenhouse experiment lasted for most of a decade, until the grant funds were used up. The people who operate it then apply what they have learned to develop better indoor planting systems in other environments. One of them is Udgar Parsons, who is Windstar's production manager. He started building the greenhouse dome under the company name Growing Spaces, LLC in Roaring Fork Valley in 1989. In 1995, he and his wife Puja moved their factory to a factory in Pagosa Springs, Colorado, where they continued to build Growing Dome in six sizes. They range in diameter from 15 feet to 42 feet, meeting the growing needs of families, schools, and community groups throughout the year.
The dome has a significant advantage in the real energy-saving world. I like to think about material savings like this: a 42-foot diameter dome covers 1,400 square feet of growing space, and uses less wood than the bottom two layers of logs in a 1,400 square foot log house! And it uses smaller material size, so it is more economical to build.
Due to its aerodynamic shape, the dome is extremely wind-resistant. The consistent strong wind is evenly distributed on the triangular frame, keeping the structure down instead of blowing it away. Rectangular frame greenhouses require heavy trusses and important cross supports to maintain their structural integrity under high wind loads; this structure makes rectangular greenhouses inherently more expensive.
Finally, the dome geometry provides a lid with the smallest surface area and the largest volume, making it the most energy-efficient enclosure we can create. Any other shape will have a higher surface area to volume ratio, which will result in more heat being lost to the outdoors. One disadvantage is that due to the large number of seams between the triangular glass panels, the possibility of failure and maintenance may increase.
Despite their many advantages, dome structures also have cultural disadvantages that we call "hippie shame" because they were widely used by young countercultural practitioners in the 1960s. If Buckminster Fuller invented the geodesic dome after the emergence of hippie culture in the 1960s and 70s, the geodesic form might be more widely accepted as an effective structural solution to many space creation challenges, including greenhouse. Fortunately, school-age children in the early 21st century did not have any such cultural baggage, which makes the growing dome an ideal greenhouse solution for edible campus projects.
We helped organize our own community to raise resources to build growing domes and outdoor gardens at two local high schools. These domes function very well as science laboratories and are also a local source of fresh produce from the school cafeteria. In the Rocky Mountains, we like to say that there are two ways to teach agricultural biology in our school: either change the school year from February to November, or build a greenhouse. Most schools in temperate regions face the same choice, and the only option compatible with our cultural calendar is to build a greenhouse.
In order to grow various plants, including tropical perennials, in our AgBio greenhouse, we first build climate batteries underground, and then lay the foundation and erect a dome on them. Last winter, when we experienced the first deep cold wave, it dropped below -10 degrees Fahrenheit for several consecutive nights. The solar heat we stored underground helped to keep the climate inside the dome at more than 30 degrees, close to 50 degrees. Fahrenheit is different from the outside world, and it is almost warm enough to prevent bananas, papaya and everything else from being damaged. When the outdoor temperature is below 10 degrees Fahrenheit, we do use some spare heat, but climate batteries can handle extreme weather to this point, saving more than 75% of energy, traditionally provided by fossil fuels. Like all greenhouses, these efficiencies depend on the actual conditions of the site and the elements contained, which are specific to each greenhouse and can be endlessly improved.
Reprinted with permission from The Forest Garden Greenhouse by Jerome Osentowski and published by Chelsea Green Publishing, 2015.
Image courtesy of Chelsea Green Press
In "Forest Garden Greenhouse", the successful permaculture designer Jerome Osentowski showed how to use efficient technology to bring forest gardens indoors, even in difficult terrain and cold climates.
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