What information can you give me on movable high tunnels?
D.S.North CarolinaAnswer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service. I am pleased to provide you with information on movable high tunnels.A moveable high tunnel offers all of the climatic benefits of a permanent high tunnel with the addition of managing soils for pests, diseases, and nutrients. Moving high tunnels has been practiced for over one hundred years, but modern designs, management practices, and research have made moving high tunnels a rather new component to season extension. Movable high tunnels require more management than permanent high tunnels but they offer a short payback in costs while providing long-term soil fertility and disease control.Maine organic farmer and author, Eliot Coleman, describes several of the advantages of a mobile greenhouse in his book, The New Organic Grower. One advantage Coleman describes is having more natural soil conditions that are not available with permanent structures. By moving high tunnels, many natural soil cleansing and balancing processes occur because the soil is exposed to such elements as rain, wind, snow, direct sunlight, and freezing temperatures (1). This advantage allows for a wider crop rotation that can include the use of cover crops and green manures. By incorporating the use of mobile greenhouses in to his crop plan, Coleman saves money and energy that would be needed for heating and cooling. For example, he can place a moveable high tunnel over an early planting of warm-season crops, such as tomatoes. Once the tomatoes are finished producing in the fall, the high tunnel is then moved over an August-planted cool-season crop to protect it through the late fall and early winter. As these crops are harvested, beds are replanted with late-winter and early spring cool-season crops. The high tunnel is again moved to receive summer-crop transplants once the late-winter/early spring cool-season crops mature. For these crops to be grown in a stationary greenhouse, a heating and cooling/ventilation system would be required.Several high tunnel companies now offer movable high tunnel kits. Likewise, many farmers have designed their own methods for moving high tunnels. This includes all of the possible ways to move the tunnel, such as by hand or by tractor. Although it is important for any high tunnel to be well-built to withstand heavy rains, winds, and snow loads, it is even more important that a movable tunnel be structurally sound. The structure needs to be strong enough to not twist during the moving process. This may require the addition of more braces than what is usually required in a stationary high tunnel. In fact, Colman’s has designed his mobile greenhouses to be moved along a wheel-and-rail system, now referred to as a V-Track. Another good example of a movable high tunnel rotation is from Heritage Prairie Farm, in Illinois. Following the guidelines set by Coleman, farmers Mike Bollinger and Katie Prochaska built their high tunnels on angle iron with five wheelbarrow wheels on each side. The 30×48 foot unheated houses can be moved to a new location by four people (3). Ideally, each tunnel is moved three or four times per year. For example: Carrots are seeded in the tunnel in February. By mid-April, they are mature enough to be outside under row cover, so the tunnel is pushed away to open ground. Tomatoes are then planted in the tunnel, where they bear much earlier than field tomatoes. In late summer, spinach is planted outside, where it grows until November, when the tunnel is pushed back over it, extending harvest into December. As the spinach finishes up, the tunnel can be moved again to another crop, such as leeks, which can be harvested until February, when it’s time to start carrots again.ResourceByczynski, Lynn. 2010. “Movable Hoophouses: The Next Generation.” Growing For Market. March 1. References1. Coleman, Eliot. 1995. The New Organic Grower. White River Junction, VT: Chelsea Green Publishing. 2. Four Season Tools. 2009. “Our Method: Spacing Between Mobile Greenhouse Lots.” Kansas City, MO: Four Season Tools, Retrieved March 28, 2011. (http://movablehightunnels.com/index.html).3. Growing for Market. 2009. “A Movable High Tunnel.” Growing For Market, Jan.1. Further ResourcesFour-season growing in movable tunnels is explained fully in Eliot Coleman’s Winter Harvest Manual, available for $15 at www.growingformarket.com or 800-307-8949.Four Season Tools 602 Westport RdKansas City, MO 64111Phone: 816.444.7330Fax: 816.561.5052E-mail: firstname.lastname@example.org