High tunnels are greenhouse type structures that do not use mechanical heat, instead they rely on the following to heat the house:
1. Direct solar gain
2. Thermal capacity of the earth
3. Optional thermal contributions from a biologically active soil or composting
They also differ from greenhouses in that they utilize natural ventilation instead of fans.
These structures offer several advantages to the market grower. High tunnels extend the season of cold sensitive crops and often allow the production of cold weather crops throughout the winter. High tunnels also protect crops from wind and moisture thus increasing yields, reducing diseases and increasing vegetable quality.
Quite diverse crops can be grown in high tunnels. This diversity can include small fruits (strawberries, raspberries...), cold hardy crops (kale, collards... ), warm weather crops (tomatoes, peppers, eggplant...), cut flowers and herbs.
Thermal performance can be increased by using low inner tunnels (or row covers), insulating pathways, perimeter insulation, different inner and outer film materials and an inflated double poly roof.
In addition, transplants can be grown without direct fossil fuel by using compost heated frames within the high tunnel. This type of system can also add significant amounts of CO2, three times ambient levels. This enhanced environment dramatically increases photosynthesis and coresponding plant growth. Poc choi planted in the mid-winter has matured in less than 4 weeks after transplanting.
For a brief article about our system please refer to the Rodale Institute's two part web article (please note that our contact information has changed since the article)
For more indepth information, check out a free 74 page High Tunnel Handbook, that I co-authored for Northeast SARE.
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Winter Harvest in the snow |
