What is a High Tunnel
High tunnels are unheated, plastic-covered structures that provide an intermediate level of environmental protection and control compared to open field conditions and heated greenhouses. In high tunnels, seeds and transplants are planted directly into the soil rather than in pots or flats, or on benches or tables. Since there is no cement slab or heating system, construction costs are lower with a high tunnel.
In order to determine the effectiveness of a high tunnel in our area, temperatures were monitored at various locations both inside and outside of the high tunnel during the winter of 2003-2004. The chart shows that while outdoor temperatures dropped to -12°F on several occasions, soil temperatures inside the tunnel under the row cover remained at or above 28°F (early February). By early March, soil temperatures were above 40°F, the minimum soil temperature necessary for germination of some “cool season” vegetables. Air temperatures under the row covers remained above 20°F until early January. As a result, we harvested salad greens until that time and gained a very early start to our spring planting.