Patrick Byers is a regional horticulture specialist with University of Missouri Extension, headquartered in Springfield. He provides horticultural outreach activities to nine counties, and has worked with high and low tunnels since 1989.

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High Tunnels and Low Tunnels
by Patrick Byers    

By building high or low tunnels, you can extend the gardening season throughout the fall and begin spring planting earlier. Here’s how.

 


These raised beds are covered with low tunnels constructed with plastic hoops. Netting stretched over the hoops protects the vegetables from deer and birds.

My vegetable garden is a place of exercise and relaxation, but my ultimategoal is to grow food. Unfortunately, inclement weather, spring and fall frosts, insects, bird pests and deer reduce my garden’s productivity. Through the use of inexpensive and easily-built high and low tunnels, I can address these challenges that face all vegetable gardeners in the Midwest.

What is a tunnel? Basically, a support system, anchored to the ground, that holds a protective covering above the vegetables. High tunnels are often a semi-permanent part of the garden, covering a larger area and allowing the gardener to work within the tunnel. Low tunnels generally cover a single row or bed, and are easily placed and removed as needed.

The design of the support system for a high or low tunnel is determined by cost, application, and the ingenuity ofthe gardener. With high tunnels, especially those that are permanent and must stand up to wind and snow load, supports should be strong and durable. Welded wire fencing panels, commonly 50 inches by 16 feet, can be bent into a support shape. Plastic PVC pipe, generally 1-1½-inches in diameter, can make effective bows. Durable high tunnels can be built using metal pipe, such as the top rail from chain link fence, bent to the proper shape. Low tunnels are supported by a wide range of materials, including light metal pipe bent to shape, heavy wire hoops and plastic pipe.

Anchoring

Permanent and semi-permanent tunnels are often anchored to the ground using baseboards of a rot-resistant wood. The baseboards are attached to metal stakes or anchors that are driven into the soil. Metal or PVC high tunnel hoops can be set inside larger diameter pieces of pipe that are driven into the soil, or set in concrete. The metal or wire hoops for low tunnels are generally pressed into the soil. Tunnels can be further stabilized with ropes stretched over the tunnel and attached to stakes driven in the soil or hooks on the baseboard.

Protective Coverings

A wide range of protective coverings are available; choose the covering that meets the need. Greenhouse-grade 4-mil polyethylene plastic film will give several years of use for tunnels intended to extend the gardening season. Heavyweight spunbonded row cover will provide similar cold weather protection, particularly when several layers are placed over a high or low tunnel. Lightweight row cover or fine netting provides protection from insects. Larger mesh netting excludes birds and deer.

A word about ventilation with plastic film-covered tunnels — the temperature inside a sealed tunnel warms rapidly on sunny days to a point thatplants are damaged, and ventilation is needed to remove this heat. Ventilation is provided by sides that roll up or down, as well as ends that open. What this means, of course, is maintenance — the gardener opens and closes the tunnel to provide needed ventilation. Ventilation is usually not as much of a concern with row covers, which allow excess heat to escape through the fabric.

Two Designs: High and Low

I’d like to discuss two easily constructed tunnel designs.

The first is a high tunnel that uses fence panels for support. A baseboard frame is built of 2-by-6-inch lumber, 8 feet wide and 21 feet long, attached on the outside face to metal stakes driven into the soil. Fencing panels are bent into a “U” shape and placed inside the frame. The fence panelsare connected with plastic zip ties, and the ends are attached to the baseboard with a board strip. Five panels are needed for this dimension; larger tunnels are easily constructed using additional panels. The panels were covered with a single layer of plastic film, which is attached to the baseboard with furring strips. The end walls were constructed of plywood, with a ventilated door that is opened when needed. The high tunnel has about 6½ feet of headroom and plenty of growing space.

The second design is a semi-permanent low tunnel, which uses ¾-inch metal pipe that is 10 feet long for support. The pipe is bent into the desired hoop shape using a template, allowing for coverage over a 4-foot-wide bed. The hoops are placed 3 feet apart over the bed, pressed into the soil, and connected with a purlin, using duct tape. A 2-by-4-inch baseboard is attached at ground level along the upwind side of the hoops, using a screw through each hoop. A wiggle wire channel is attached along the upper face of the baseboard, and the covering is attached with the wiggle wire. The covering is stretched over the hoops, and secured on the other side with sand bags. The covering ends are bundled together, tied, and secured to a stake driven into the ground. This tunnel is intended to provide for winter vegetable production and for protection from insect pests during the remainder of the growing season.

 

Low Tunnel Construction



A low tunnel is easily constructed using metal bows bent to the proper shape.

 


Pressed into the soil over the bed and stabilized with a purlin.

 


Connected with a baseboard that also serves to anchor one side of the covering with wiggle wire.

 


And a covering secured with sand bags.

 

 

A version of this article appeared in a September/October 2015 print edition of State-by-State Gardening.
Photography courtesy of Patrick Byers.

 

 

Posted: 09/05/18   RSS | Print

 

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