Tunnel Farming Adds Weeks to a Short Growing Season

For everything there is a season, but for fresh produce grown in the Upper Midwest, it can be a frustratingly short period of time. It’s a hard truth that local food lovers in colder climes have accepted with resignation: enjoy the seasonal bounty of fruits and vegetables while you can, before the growing season quickly comes to an end. For many of us, the abbreviated availability of certain fresh foods make the concepts of eating locally and seasonally seem incompatible for a good portion of the year. But now, an emerging farm technique is stretching the traditional boundaries of the growing season and could help bring the local and the seasonal together under its roof. 

Early Surprises

Mother’s Day weekend at the Minneapolis Farmers’ Market was a cold and blustery reminder that summer – and many popular fruits and vegetables of the season – are still several weeks away. So, it was quite a surprise to see lovely heirloom tomatoes and crisp green beans on display at Abraham Bauman’s Real Foods stand, while across the aisle, bunches of tender leaf lettuce were being offered by Don and Shari Heinel of Heinel Farms. How could it be that these summer vegetables could actually be locally grown and yet be offered so early? 

It turns out that both Bauman and the Heinels have embraced tunnel farming – an agricultural practice that extends the growing season and produces high quality, high yield crops without increased use of energy resources or pesticides. As the benefits of this method become better known and more widely implemented, both growers and consumers stand to reap the rewards. 

The High and Low of Tunnels

When it comes to tunnel farming in Minnesota, there are probably few people who know as much as Terry Nennich, a professor with the University of Minnesota Extension Service and a driving force behind UMN’s High Tunnel Production project. Ever since he first saw the structures 10 years ago during a visit to Normandy, France, where they are widely used, the Extension educator has been researching and promoting the benefits of tunnel farming in the Gopher State. 

According to Nennich, it is a bit like growing plants inside a greenhouse, but the similarities end there. Unlike greenhouses, tunnels are temporary structures that range in height from just one to two feet off the ground ("low" tunnels) to nine to twelve feet tall ("high" tunnels). Their metal or plastic hoop-like frames are covered with specially designed plastic sheeting that efficiently retains solar heat and can be rolled up or down to manage air flow. As a result, there is no need for any electrical or mechanical systems to generate heat or to manage ventilation inside these "hoop houses."

“You get about five to six weeks earlier production in the spring and several weeks later in the fall,” Nennich explained. “The plants are still put in the ground, just like they would be outside.” However, as opposed to crops planted in the open, those in tunnels are much better protected from insects, foraging animals, and extreme weather conditions, such as strong winds, hail or frost, which can cause extensive damage to outdoor produce. By extending the growing period and minimizing external environmental threats, tunnel farming can yield substantially more than their open-air counterparts.

In a 2009 report on an organic vegetable farming experiment conducted by Nennich’s High Tunnel Production team, the comparable yields between tunnel and outdoor plots were remarkable:

  • On average, tunnel vegetables such as lettuce, tomatoes and cucumbers were harvested about six weeks earlier than those grown in the open, while peppers were ready nearly ten weeks ahead.
  • Yields by weight were equally impressive, with many of the tunnel plants producing as much as double the output of the outdoor crops.

With those kinds of results, tunnel farming is quickly gaining ground with growers: in 2007, there were an estimated 150 high tunnels in Minnesota and approximately 200 by the following year. Earlier this year, the state branch of the USDA’s National Resources Conservation Service (NRCS), which has been working with the High Tunnel team, announced that funding for high tunnel construction would be available for the first time; as of two weeks ago, 240 applications had been received for the 100 grants available. 

Early Adopters

Two growers who didn’t wait to start tunnel farming are Abraham Bauman of Real Foods in Athens, Wisconsin, and Don Heinel, the fourth generation to run his family’s farm in Little Canada, Minnesota. In a neat bit of coincidence, not only do these two gentlemen farmers set up their stands across from each other at the Minneapolis Farmers’ Market, they also represent the two sides of the tunnel farming aisle. 

Bauman has been using high tunnels for 13 years to grow his certified organic vegetables, which are available through CSAs in Madison, Wausau and Minneapolis, as well as local farmers’ markets in those areas. Although he doesn’t quite recall how he first learned about tunnel farming, he knew what he wanted. “I thought about what I needed to do to enhance the environment for my crops,” Bauman explained. The practice, he added, “gives you a little more control of your environment so you can take care of the plants better.” 

That extra care is evident in Real Foods’ vibrant market offerings; during a recent Saturday at the Lyndale market, brown eggs and green beans sat alongside colorful heirloom tomatoes in hues that ranged from deep red to bright yellow and rich purple. With high tunnel farming, Bauman can grow his produce using certified organic practices and the extended growing period allows him to plant as many as 50 different varieties of tomatoes throughout the season, including such uniquely-named beauties as Dr. Wyche’s Yellow, Green Zebra and Prudens Purple. 

At the other end of the tunnel spectrum, Heinel is entering his third year of growing vegetables in low tunnels, which he chose over the walk-in structures for admittedly basic reasons. “I’m slightly lazy,” he said jokingly, before explaining, “My father helps me a bit but he’s 82. We try to be as efficient as possible in every movement we make when we farm.” He felt that the taller hoop houses would require much more time and involvement than he could provide – a conclusion confirmed by Nennich, who noted, “The management is very, very intense. You have to learn how to control the heat, how to control the water and the environment. You’re trading your management time from farming large acreage.”

Low tunnels still provide Heinel with many of the same benefits, while also giving him the flexibility to innovate and experiment. During his first year of tunnel farming, he applied plastic covering over the frames using a pole through the sheet roll; the following year, he built a machine to do the job with much less effort. Currently, Heinel is experimenting on his lettuce crops using a mesh-like cover material. “It’s mainly to keep critters, meaning deer, from eating my lettuce,” he said. However, he also noted that the heat of summer can sometimes make the leaves taste a little tart or bitter and so he’s using part of his mesh experiment to see if more shading in the tunnel will affect the flavor: “You don’t want to leave the customer with a bad taste in their mouth!”

Although their chosen methods differ and their years of experience are far apart, both Bauman and Heinel agree that tunnel farming makes excellent business sense. “It extends the harvest period and with the short growing season that we have in this area, that’s a real plus because you can add months,” said Bauman. “The bottom line is that it’s profitable.”

Heinel also recognized the advantage of having earlier crops. “If I could be two or three weeks ahead of everybody else, that would be a portion of the season I could establish a customer base of people who would become more familiar with my quality,” he explained.

Because tunnel farming protects crops from damaging external factors, it offers growers and their business clients some stability in supply. “It creates a trust factor between the producer and the specialty crop market like restaurants, who don’t have to worry about being called the morning they’re supposed to get a shipment and be told, ‘Gee, we had two inches of rain last night and we can’t pick it,’” said Nennich. But he points out that while the economic advantages for growers and related businesses are undeniable, the biggest winners in the long run will be produce-loving consumers. “People are going to have healthful foods that are very nutritious and available for a long period of time in the summer.” 

Tunnel Vision

If research by UMN Extension’s High Tunnel Production team is fruitful, produce buyers will have more choices in the future. Farmers like Bauman and Heinel use tunnel farming to maximize their production of fruits and vegetables that are already well suited to this region’s environment, but the system could potentially allow them to grow crops locally and seasonally that must otherwise be shipped from distant locales. “I see tunnels going to sweet potatoes, which are awful risky outside if you even get a crop at all,” said Nennich. At the moment, he and fellow researchers are focusing their energies on fruit production, having built two new research tunnels near Crookston to grow small fruits such as raspberries, blueberries and blackberries, while another tunnel will house apple and other fruit trees. 

The controlled climate of tunnels is also environmentally friendly: because the plants are better protected against insect and pest infestation, pesticide use is limited, if used at all. Nennich also estimates that water usage is at least 20 percent less than with outdoor planting, due to low moisture evaporation in the tunnels. The need to further explore the environmental benefits is one of the reasons that the NRCS decided to give grants to farmers who would like to adopt tunnel farming. 

The Big Question

After all the discussion about energy efficiency, extended growing seasons and economic benefits, it really boils down to one question: how good is tunnel-farmed produce? Very good, according to Nennich, since high tunnels allow vegetables like tomatoes to mature longer on the vine and ripen naturally, as opposed to being picked green and then gassed with ethylene to achieve the desired red color. Heinel reports that his tunnel lettuce is more tender, although the color of the leaves are not as deep as those grown outdoors, while Bauman notes that his produce offerings have a better appearance since they’re not subjected to the vagaries of weather. 

As for the flavor of tunnel-farmed produce, that must be left to individual tastebuds to decide. The good news is that if you’d like to try a Brandywine tomato from Bauman’s Real Foods or Heinel Farm’s delicate lettuce, you now have plenty of time in the season to enjoy them.

For more information about high tunnel farming, please visit the University of Minnesota High Tunnel website at or contact:

Abraham Bauman, Real Foods – (715) 574- 0035

Don and Shari Heinelm, Heinel Farm – (online contact form)

Tracey Paska, a student at the University of Minnesota, is pursuing a self-designed degree in food studies, which combines coursework in anthropology, history and sociology as they pertain to the foods we eat. She was born in the Philippines, but now lives in the western suburbs of Minneapolis. When she's not composing research papers, she writes about the complex, confusing and fascinating connections between food, culture, and society on her blog Tangled Noodle. Her last post for Simple, Good and Tasty was A Very Prairie Cuisine.