Overview: High Tunnels

Virginia Vegetable, Small Fruit and Specialty Crops
May-June 2003; Volume 2, Issue 3

Chris Mullins Virginia State University

What is a High Tunnel?
A High Tunnel is a simplified growing system that enhances crop growth, yield and quality. Similar to heated greenhouses, high tunnels are used to extend the growing season in the spring and fall and are useful with a variety of crops; however, they lack all of the electrical components and automation of a conventional greenhouse. Basic components of a high tunnel are a metal Quonset shaped frame, single layer of polyethylene cover and an irrigation system. Crops are grown in the ground, yet are protected from temperature fluctuations and light frost. Other benefits are reduction in moisture fluctuation, wind protection, soil warming, reduced chemical usage and the ability to use biological pest control.

High tunnels are relatively inexpensive allowing for protected vegetable production with a limited capital investment. The system is most appealing to direct marketers, who can take advantage of having out-of-season produce which can be sold at a premium price.

What crops can be grown in a high tunnel?
Many crops such as tomatoes, cucumber, peppers, strawberries, broccoli, brambles, and cut flowers do very well in a high tunnel. Specific crops, which might be grown, will largely depend on marketing opportunities available to individual growers. Much work has been done at Pennsylvania State University with high tunnel structures and the different crops that are best suited to these structures. When used along with other plasticulture components such as drip irrigation and plastic mulch, a high tunnel can produce high quality crops 3-4 weeks early in the spring and extend the growing season in the fall by 3-4 weeks.

How is a high tunnel constructed?
High tunnel frame packages can be purchased from many different suppliers, so always follow the construction instructions that come with your frame. Generally, the frame for a high tunnel is composed of various 1-2" galvanized metal pieces and hardware. The first step is to drive the 3' ground posts into the ground, leaving 1' above ground. These posts should be placed 4' on center. With the posts level side-to-side and the corners square, the next step is to construct the bows. Metal bows usually come in 2-3 pieces and give the structure it's shape. Bows can be constructed on the ground, then lifted into position and fitted into the ground posts. Placement of the horizontal metal tubing called purlins is the next step. Purlins span the length of the structure and are bolted to the bows. Normally, there are three purlins for each structure, one at the ridge and one on each side of the ridge. The purlins along with the corner bracing give the structure stability. Along the ground on the sides of the structure are the baseboards. These are usually 2" x 8" treated lumber that touch the ground and are bolted to the ground posts. The frame will be complete after hipboard (1" x 4" lumber) along with poly lock is attached to the bows approximately 5-6' off the ground. This will serve as the point of attachment for the plastic covering.

The end walls are the next step in construction. Generally, these are framed from 2" x 4" treated lumber and can be built either fixed with a passage door or semi-fixed with a large hinged door. The large door that spans the width of the tunnel will allow for movement of equipment in and out. Next, the 6-mil greenhouse grade plastic can be attached to the hipboard, along the end bows and to the end walls. This is best done early morning or late afternoon when there is less chance for wind. The last construction step is to attach the plastic at the baseboard to a length of 1" metal tubing with PVC clips. This will allow the plastic to be rolled up to the hipboard. Ventilation in the tunnels is accomplished by rolling up these sidewalls.

What is the cost of a high tunnel?
Approximate Costs for 21' x 48' High Tunnel Structure:

Metal Frame	$1,400.00
Poly cover and lock	460.00
End wall lumber	265.00
Irrigation	125.00
	$2,250.00
Construction labor 60hrs @ 8/hr.	$ 480.00

For more information:
Chris Mullins, Virginia State University, PO Box 9081, Petersburg, VA 23803 (804) 524-5834 / cmullins@vsu.edu

Editors note: Penn State has recently released the new "2003 High Tunnel Production Manual" which covers everything from history, construction, to environmental management, all phases of production, pest management, economics, and references. It is 152 page plus three appendies. The manual is for sale at $25.00 and for bulk orders of 20 or more copies the price is $20. Orders can be sent to Dr. Bill Lamont at the address below:

Dr. Bill Lamont, Department of Horticulture, 206 Tyson Bldg., The Pennsylvania State University, University Park, PA 16802

Please make checks payable to: The Pennsylvania State University.

References
Butler, B. R., Extending the Production Season for Vegetables and Small Fruit. Univ. of Maryland Coop. Ext. Fact Sheet 760.

Wells, O.S., 1998. Rowcovers and High Tunnels-Growth enhancing Technology. Proc. of the Soc. of Hort. Sci. and Plasticulture. Sem. Series.

Wells, O. S., 1996. Row Cover and High Tunnel Growing Systems in the United States. Hort Technology. 6 (3): 172-176.

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