For centuries a wide variety of techniques have been used to extend the
growing season of horticultural crops. Glass jars, glass cloches, hotcaps,
cold frames, hotbeds, and greenhouses of various types have all contributed
to season extension. More recently, row covers and high tunnels have become
popular with growers because of their simplicity and effectiveness in
protecting crops from low temperatures in both spring and fall.
Row covers and high tunnels do not offer the precision of conventional greenhouses for environmental control, but they do sufficiently modify the environment to enhance crop growth, yield, and quality. Although they provide some frost protection, their primary function is to elevate temperatures a few degrees each day over a period of several weeks.
In addition to temperature control, there are also the benefits of wind and rain protection, soil warming, and in some instances control of insects, diseases, and predators such as varmints and birds. Overall, these growing systems should be considered protected growing systems that enhance earliness and higher yields, improve quality, and reduce the use of pesticides in some cases.
Row covers and high tunnels have sufficient versatility to make them useful on a wide diversity of crops and in various cropping systems. Vegetables, small fruits, and flowers are all suited to these growing systems; but the specific crops which might be grown will to a large extent depend on marketing opportunities for individual crops by individual growers.
High tunnels encompass a crop growing system that fits somewhere between row covers and greenhouses. They are relatively inexpensive (about $1.30/sq. ft, excluding labor), permitting entry into high tunnel crop production with limited capital. This system is particularly appealing to new-entry growers who utilize retail-marketing channels.
High tunnels are not conventional greenhouses. But like plastic-covered greenhouses, they are generally quonset-shaped, constructed of metal bows that are attached to metal posts which have been driven into the ground about two feet deep. They are covered with one layer of 6-mil greenhouse-grade polyethylene, and are ventilated by manually rolling up the sides each morning and rolling them down in early evening. There is no permanent heating system although it is advisable to have a standby portable propane unit to protect against unexpected below-freezing temperatures. There are no electrical connections. The only external connection is a water supply for trickle irrigation. Dr. Otho Wells was a pioneer in promoting the use of high tunnels in the northeastern United States and developed the New Hampshire design and system of production that involved covering the entire soil surface inside the tunnel with a solid sheet of 6-mil thick plastic. At Penn State we re-designed the endwalls so that they can be raised up to facilitate easy access into the tunnel of a small tractor and tiller and a system of production that uses 18- inch wide raised plastic mulch covered beds with drip irrigation tape buried 2-3 inches beneath the bed. The raised mulch beds are 44 inches apart, which allows 4 rows in a 17 foot wide high tunnel.
At Penn State a tremendous amount of research and extension programming is oriented toward high tunnel production of vegetables, small fruits, tree fruits and flowers.
A High Tunnel Production Manual is available for purchase. Follow this link for more information.
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High Tunnel Production of Cucumber on Raised Beds
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High Tunnel Tomato Variety Trial
Penn State High Tunnel Extension Program (pdf)
Design and Construction of the Penn State High Tunnel (pdf)
Production System for Horticultural Crops Grown in the Penn State High Tunnel (pdf)