The Benefits of Building a High Tunnel

A simple high tunnel framework covered with plastic defeats inclement extremes and extends the vegetable gardening season.
By George DeVault
September/October 2012
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High tunnels like this one shelter plants from pests and extremes, allowing for higher yields.
George DeVault
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Rain is pouring down — again. We’re already some 23 inches above average precipitation on the year, and it’s only September. However, my crops and I are nice and dry, thanks to the largest of the four high tunnels I built on our small farm in southeastern Pennsylvania.

What’s a high tunnel? It’s a poor man’s greenhouse. Instead of expensive glass and intricate steelwork, the structure consists of a simple frame — usually made of bent galvanized metal pipe or PVC pipe, though wood can be used. The pipes that form the “bows” or “ribs” of the frame fit into slightly larger diameter pipes that are driven two or three feet into the ground to form the foundation. Smaller PVC pipe is sometimes slipped over pieces of rebar hammered into the ground. The whole thing is then bolted together with baseboards, purlins, end-framing and doors to meet your needs.

The frames are covered with one layer of 6-mil UV-resistant greenhouse plastic. The plastic is attached with everything from expensive aluminum channels and “wiggle wire” to wooden lath, old fire hose, strips of inner tube, and even used drip-irrigation tape. The tunnels are not heated, but having an emergency heat source handy is cheap insurance for protection from extreme cold snaps, heavy ice or snow.

Whether you’re a backyard gardener, a market gardener or a commercial grower, you can build a high tunnel to meet your needs in just a couple of days using simple hand and power tools.

Benefits of building a high tunnel

The “high” part of the name means that the tunnel is high enough that you can stand up straight inside. “High tunnel” is a somewhat loose term. It includes everything from tall, Gothic arch structures to Quonset-style “hoop” houses, which also are known as cold frames. In tunnels with high sidewalls, there is plenty of room to operate garden tillers and even small tractors with tillers, mulch layers and bed shapers.

In extreme heat, the plastic skin can be easily shrouded in, or even replaced with, shade cloth. Add drip irrigation, minisprinklers and maybe a fan or two, and crops inside the tunnel will be almost as cool as veggies in the supermarket produce case.

Using plans available for free on the Internet and parts from a local building supply center, you can build a moderate-sized high tunnel for about $500. Commercial-sized kits with predrilled steel frames, usually 96 feet long and anywhere from 14 to 35 feet wide, start at $3,000 to $6,000, respectively. Don’t forget to tack on freight, lumber, the plastic skin and whatever upgrades strike your fancy.

High tunnels are so cheap to construct and operate that a grower can recoup the cost of construction in one to two years’ time, according to a 2009 report in HortTechnology magazine, published by American Society for Horticulture Science.

The payback period depends on many factors, starting with what you grow, how you grow it and where you sell it. We sell everything directly to consumers at two nearby farmers’ markets in Emmaus and Easton, Pennsylvania.

So, while a cold fall rain drummed steadily on my high tunnel’s plastic skin, I harvested 16 1/2 pounds of baby Swiss chard, 12 pounds of spinach, 25 pounds of plum tomatoes, 8 pounds of arugula, 7 pounds of kale, and our most popular item: red raspberries. Throughout one week, I picked and stockpiled 26 half-pints of perfect berries. Since the berries have been protected from rain, they don’t develop gray mold overnight. The huge, tasty berries easily keep for a week in our walk-in cooler, then sell out in record time at $5 a box.

Outside, water stood ankle-deep in the saturated fields. My snap beans rotted. A promising crop of fall sugar snap peas drowned. It was a miserable year. A soggy spring was followed by a serious dry spell with record temperatures up to 104 degrees for what seemed like forever. Then came Hurricane Irene and a record 13.47 inches of rain in August. September started with Tropical Storm Lee and more flooding.

The month ended with a record 12.77 inches of rain. But Mother Nature was just getting warmed up. The Halloween nor’easter of 2011 buried a huge area from West Virginia to Maine under sometimes 30-plus inches of snow on October 29 and 30. Colorful leaves still clung to the trees. Heavy snow piled up on the leaves. Branches, trees and power lines soon crashed down everywhere. Millions of people were plunged into darkness for a week or more in some places.

“While Matt and Jess of Salvaterra’s Gardens braved the weather last weekend to sell their produce at Centre Square, snow was quickly piling up at the farm. When all was said and done, their crops lay buried under 15 inches of wet, heavy snow,” Megan McBride, manager of the Easton farmers’ market, wrote five days later in her weekly e-newsletter to the market’s thousands of regular customers. “Matt reported that while they lost an ample amount of cooking greens ... much of their lettuce was protected by high tunnels.”

We had at least that much snow at our farm a few miles away. But by noon Sunday, gravity and the returning sun had almost magically cleared the snow from our Gothic arch tunnels. Inside, the greens, raspberries and even a few late-season flowers looked like it was still summer.

“As the weather seems to be getting increasingly erratic, high tunnels provide insurance. Even if your tomatoes get hailed out or your lettuce rots from too much rain, your high tunnel veggies will keep producing,” the Kansas market gardener says.

John Biernbaum couldn’t agree more. “Based on 10 years’ experience building a wide range of high tunnels, growing a wide range of crops, and helping dozens of farmers and market gardeners get started, high tunnels have proven to be very reasonable and economical to build, either from commercially available kits or a combination of local and ordered parts,” says the Michigan State University horticulturist and professor.

“Tunnels allow dozens of high-value crops to be harvested out of season. They provide risk management and crop protection from cold, excess rain and some insects, while increasing production from small growing areas. Still, adoption of high tunnels seems slow. High tunnels seem like the ideal strategy for health care related to eating more vegetables and fruit and economic recovery, except that you have to actually eat vegetables and some physical activity is required,” he says.

Maybe that’s why the United States Department of Agriculture (USDA) is actually paying people to build high tunnels. Since late 2008, the Natural Resources Conservation Service (NRCS) of USDA has provided financial assistance toward the cost of more than 3,800 new high tunnels on farms in 43 states.

Using these structures, it’s fairly straightforward to convert solar energy into a bounty of fruits and vegetables in an environment where it would otherwise be impossible. It also extends the growing season, so farmers make more money while farmers’ market customers benefit from more fresh, local produce. To find out more about government incentives for constructing a high tunnel, contact your local NRCS office or visit Natural Resources Conservation Service.

High tunnel construction considerations

If you can swing a sledgehammer, use a tape measure and a rechargeable drill, you can build a high tunnel. It’s not rocket science (for a few tips from us see the Image Gallery). The instructions for the first tunnel I bought in 1991 consisted of just 102 words and five simple diagrams on one page. Since then, scores of books and detailed research papers have been written on high-tunnel construction and management. Today, a Google search for “high tunnels” yields 511,000 citations. One of the most helpful websites is High Tunnels. It is a partnership of extension specialists at five mostly Midwestern land grant universities and the nonprofit Kansas Rural Center. The site’s encyclopedia “resources” list puts everything you ever wanted to know about high tunnels at your fingertips.

Location, location, location

The first thing you need is a good location. It must be well-drained and level from side to side. A slight lengthwise slope is OK, and even somewhat desirable, since it will promote better air flow and ventilation. Ideally, your building site should allow good air flow in summer, plus protection from wind in winter. A windbreak is a big plus. Position the tunnel perpendicular to prevailing winds, facing more or less east-west to get more sun through more of the year. Make sure the site is not shaded by trees or nearby buildings, especially during the colder months when the sun is low in the sky.

Use some of your best, most productive ground. A high tunnel will make it produce — and earn — even more.

Convenience is another critical factor in site selection. The closer your tunnel is to your house, barn, water source, washing and packing shed, and storage areas, the better you can manage it. Doors, rollup sides and other vents have to be opened or closed frequently to keep your plants happy.

Crops under cover need regular watering, even if it is pouring outside. We drip irrigate and sometimes hand-water in all of our tunnels with garden hoses connected to faucets on the house. Electricity is optional for fans, maybe a radio and backup heat.

Once you have your ideal building site, lay out the footprint for your high tunnel with corner stakes and string. Take extra care to make sure your corners are exactly square. A 100-foot tape measure is invaluable. And make sure you exhaust efforts in securing your structure to the ground.

So, what could be better? High tunnels extend your season, increase your income, and the federal government will even pick up most of the tab for building one. If you still need one more reason to build one, just consider the long-range weather forecast.

“We’re in a pattern much like the 1950s-1970s that brought severe winters and more than our fair share of flooding summers,” says Bill Kirk, chief executive officer of Weather Trends International in Bethlehem, Pennsylvania. “This is very much tied to the start of the 30-year cold phase of the Pacific Ocean (started in 2006-2007), and that brings a much colder, but stormier Northern Hemisphere. When the Atlantic goes cold in about five years (it’s still only in year 15 of its 20-year warm phase), then we’ll have a double whammy — cold Pacific/cold Atlantic, and those bring brutal winters and colder, wetter summers.”

But why let weather stop you from the things you love most? With the help of a high tunnel, you will garden longer, garden better, and make more money at it than without, and that’s plenty of reason to build one of these structures at your place.

Build a 4-by-6-foot cold frame with our simple plans in Gardening Tips: A Cold Frame to Build.

George built his first high tunnel in 1991. Since then, he has added five more to his small farm in southeastern Pennsylvania. A seventh high tunnel is scheduled for later this year. George and his wife, Melanie, use them to produce everything from vegetables and cut flowers to pigs and raspberries. 


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Post a comment below.

 

Robyn Dolan
10/10/2012 4:55:53 PM
This sounds right up my alley. Rebar, pvc, plastic and shadecloth. I'm there.

T BRANDT
9/3/2012 10:17:01 PM
All the on-line directions for hoop house seem to call for 6 mil "UV resistant" plastic and at least 3/4" pvc pipes. I used 1/2 inchers and standard 4 mil plastic (150 ' x 25' for ~$95). It worked just fine. If you roll the ends of the plastic fairly tightly on 1" x 1/2" slats and screw them into a 2 x 4 foundation frame, the tautness of the skin against the pipes gives the structure enough integrity to stand up to the worst spring Chicago thunderstorms. ..It was nice harvesting lettuce & radishes here in May when conventional gardens were just begining to become warm enough for planting.

Hans Quistorff
8/31/2012 7:49:32 AM
I use the frames from portable garages that the tarps have worn out and replaced the cover with construction plastic that has grommets to tie to the frame. Three rows of fall Raspberries are starting to produce now and should be available through November for the farmers co-op market. To answer the other comment: I have bumble bees in my tunnel for pollination and paper wasp bees for pest control. Some pictures http://www.facebook.com/pages/Qberry-Farm/160604427305966?ref=hl

Beth Beatrice
8/29/2012 6:23:24 PM
If the plants are protected from insects, how does pollination take place?








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