Extending the Season

ACES Staff

October 29, 2014

Extending the Season

Pretty or Not, Hoop Houses Offer Beautiful Benefits

Article originally published in Edible Aspen’s Fall 2014 Issue.

Pitkin County Open Space and Trails recently acquired the Glassier Property—240 acres of prime agricultural land located off Hooks Spur Road in Basalt. This incredible property has been agriculturally productive for over 100 years, and the county—together with neighbors, recreationists and agricultural producers—recently developed a plan to keep agriculture going there for the next century while helping to incubate new farm businesses.

Surely, access to such prime farmland is a boon to local agriculture, but how will farmers adapt to the short, high alpine growing season of the Roaring Fork Valley and design commercially viable operations?

Most of the major food production regions in the U.S. have 240 or more frost-free days per year. By comparison, the Roaring Fork Valley averages about 110 frost-free days, translating into a much shorter growing season. That doesn’t mean that vegetable production here is impossible, it just requires smart on-farm decisions like electing to plant cold-tolerant crops rather than more sensitive varieties. Some farmers in the Valley are taking adaptation a step further, coping with the short season by installing hoop houses or greenhouses.

As these structures have grown increasingly popular in recent years among farmers growing everything from tomatoes to marijuana, they’ve sparked a local debate over whether greenhouses add to the beauty of our rural Rocky Mountain landscape or detract from it. With some Valley residents upset at the recent proliferation of greenhouses among the hayfields, cow pastures and barns that have characterized agriculture here for more than a century, it seems important to illustrate the critical role that greenhouses play in a viable high alpine food economy. If we understand their many benefits, perhaps we can begin to expand our definition of rural beauty to include these vital structures.

Hoop houses are really about climate modification, and when farmers install them they are adjusting more than just the air temperature inside. In fact, soil temperature is one of the most vital considerations in crop growth. Soil is a living thing and when the soil temperature drops, all of its bacterial and microbial life slows down, making it impossible for plants to receive the nutrients they need.

Maintaining optimal soil temperature is particularly important for organic crop production, which emphasizes feeding the soil so the soil can feed the plant.

Aside from altering air and soil temperature, hoop houses also reduce wind, help maintain soil moisture and, in certain cases, protect from precipitation, which can spread disease or—in the case of hail—damage a crop. They also alter the amount of light that reaches a crop and permit the addition of shade cloth to grow cool-season crops in the heat of summer.

In its simplest form a hoop house is a building frame, usually constructed with metal hoops and covered with polyethylene plastic. The structure collects solar radiation from the sun and stores it inside, boosting the soil and air temperature. According to four-season farming guru and author Eliot Coleman, a hoop house becomes a greenhouse when greater structural stability and supplemental heat are added. Sources of supplemental heat are traditionally a propane heater or woodstove, but adding thermal mass, insulation or a climate battery are other energy efficient ways of boosting the structure’s ability to store heat.

As it happens, the innovative climate battery concept has local roots: Jerome Osentowski, founder of Basalt’s Central Rocky Mountain Permaculture Institute (CRMPI), was one of the first to pioneer the idea, originally called the Subterranean Heating & Cooling System. In essence, a climate battery is a series of underground tubes connected to an air intake and air exhaust. The air intake is fitted with fans that can move warm, daytime air from the greenhouse into the underground tubes, which act like batteries and store the heat for later. In the evening, the fans can be activated again, moving the heat from underground back into the greenhouse to combat cold nighttime temperatures.

Finding the Right Balance
In the Roaring Fork Valley, season extension structures can add 15 weeks or more to the growing season. For a local market farmer, the costs of the structure can quickly pay off through a good harvest early or late in the season. Improving a hoop house with thermal mass, insulation or a climate battery adds labor, time and materials costs, but these investments generally pay off by providing several additional weeks of time to grow. Finally, employing supplemental heat can enable harvests year-round.

To be sure, hoop houses offer many advantages, but farming is a low-margin business and before investing in a large structure farmers should evaluate whether their season can be extended with a lower-tech solution. That could include choosing south-sloping fields, building raised beds, orienting beds east to west or covering the soil with plastic. All of these techniques allow the soil to warm faster earlier in the season, creating a more favorable growing medium for the plants to thrive. Other extension techniques include transplanting (starting plants indoors and moving them out, instead of direct seeding), creating windbreaks and using floating row covers for outdoor production. If, after examining these strategies, farmers desire a longer season, they can move toward hoop houses or greenhouses.

Although food production in the Roaring Fork Valley is challenged by the climate, the growing sophistication and popularity of season extension techniques is already fueling an expansion of local agriculture. Combined with increased access to open space lands, season extending structures could play a key role in helping a new generation of local farmers grow, create jobs and improve our food security, if we’d only let them.

Sidebar: The Moveable Harvest
Most stationary hoop houses are covered throughout the year, so the soil inside is deprived of exposure to rain, wind, snow, direct sunlight or freezing temperatures, which can lead to pest problems and decreased soil health. Exposing soil to the elements allows a natural cleansing and balancing process that helps to maintain healthy soil. Mobile hoop houses like the “Rolling Thunder” model found at Rock Bottom Ranch allow the entire house to move on rails, much like a railroad track. With just two people, the 26- by 48-foot house can be rolled to a new location, exposing the soil to the natural elements and allowing farmers to protect different sections of their field throughout the growing season, depending on the needs of each crop. One planting sequence that a farmer might pursue with a mobile hoop house is to plant cool-season crops like lettuce, greens and root vegetables in late winter (February 1 in the Roaring Fork Valley), then move the house around April 15 to accommodate warm-season crops like tomatoes, peppers and cucumbers in the spring, before moving it back in the late fall to keep cool-season crops alive into early winter. This would extend the harvest season until the end of October for warm-season crops and the end of December for cool-season crops.

~ Jason Smith, Rock Bottom Ranch Director

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