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What is a "high tunnel" greenhouse?

In our previous post, we talked about a greenhouse we donated to the University of Vermont's College of Agriculture and Life Sciences. What we donated was a "high tunnel" greenhouse. We have a special section on our website dedicated to this type of greenhouse. From that page is this summary:

High tunnels are an increasingly popular trend for growers and a proven technology for crop production. The term "high tunnel" is a loosely defined phrase for growing fruits and vegetables in greenhouses, although some high tunnels are used for cut flower production. High tunnels may be used to extend the growing season by providing protection for early- or late-season production, or they may be used for year-round growing. High tunnels are becoming increasingly popular due to the low start-up cost and quick rate of return on investment.

High tunnels were originally greenhouses with high sidewalls to enable tractors and tillers to easily enter and exit greenhouses from either end. These greenhouses were simple in design, with usually just one layer of poly, roll-up curtains and no electricity. Some of these greenhouses only had poly on them for a few weeks before the warmer weather allowed the cover to be removed safely without any damage to the crops. High tunnel greenhouses enabled local growers to produce crops during all four seasons and helped combat the forces of unpredictable weather, particularly in the early spring.

Today’s high tunnels may be as simple as a greenhouse frame with one layer of poly and roll-up curtains, or a more sophisticated greenhouse that is "moveable" and has roof vents, year-round covering, an irrigation system and heat. These freestanding greenhouses are available in all different widths and lengths. The most common use of a high tunnel is for tomato production, and is usually a 30-foot by 96-foot greenhouse; however, many other crops are being grown in greenhouses, including cucumbers, lettuce, strawberries, raspberries and herbs. Recognizing this trend in growing, seed companies have began to specialize in offering greenhouse-grown seed varieties and other unique varieties for heirloom and organic growing. High tunnels are all customized to meet the individual grower's needs and are specific to the crop that is being produced.