High tunnels, high profits: Extension specialist unlocks the potential of plants, plastic and sunshine

It’s a giant structure made of metal frames and one – or sometimes two – covers of plastic. It’s a cost-saving and profit-making aid for farmers who want to increase production and grow in both hot and cold climates. And yet growers and researchers are still unlocking the many possibilities of the high tunnel.

Sanjun Gu, Ph.D., a horticulture specialist with Cooperative Extension at N.C. A&T, has spent years researching the complexities of the high tunnel and its attributes. He has spent the past several years attempting to answer a fundamental question: do farmers in North Carolina need a single or double layered tunnel for plant production?

High tunnels, or “hoop houses”, are an increasingly popular, affordable tool for growing crops in all seasons and climates. Although they appear similar to the common greenhouse, the difference lies in the structure and usage: while greenhouses are typically constructed of glass and metal with plants grown in above-ground pots, high tunnels use more cost-efficient plastic, polyethylene, or fabric covers with plants grown directly in the ground or in raised beds.

When Gu, a former state vegetable specialist at Lincoln University, arrived at N.C. A&T in 2013, there were three high tunnels in use at the University Farm. Although there were great projects underway with those tunnels, Gu said, he saw room for growth.

“When I got here, I looked at what we had and looked at the research of neighboring states like South Carolina, Georgia and Virginia,” said Gu. “I quickly realized that there wasn’t much research going on….I said ‘Well, let’s do something about this.’ ”

In the next nine years, Gu’s high tunnel work secured more than $3 million in grant funding, with donors including the Specialty Block Grant Program, the Wal-Mart Foundation, the USDA Organic Research and Education Initiative and Evans-Allen, one of the research programs of USDA’s National Institute of Food and Agriculture. And yet one question continued to intrigue Gu: do farmers require one or two covers when working in high tunnels?

“People always wanted to know the answer, and that was, ‘In North Carolina, especially in the Piedmont [Triad], should we cover our high tunnels with one or two layers?’ ” said Gu. “It took a while. It took me up until two or three years ago before I finally had enough high tunnels to perform that kind of study. Now we have six tunnels to study using one layer versus two.”

Following a $650,000 Evans-Allen grant in 2020, the six high tunnels included in the project include four 30’ x 96’ stationary tunnels and two 30’ x 48’ moveable tunnels. As an integrated study, several concurrent projects were implemented to gather information on the effectiveness of the high tunnel and the single vs. double layer issue. Crops such as tomato cultivars (Big Beef, Rebeski and Brandywine), bell peppers (Sunrise and Olympus) and eggplant cultivars (Traviata and Oriental Express) were grown in in both single- and double- layer conditions and harvested to ripeness.

Several variables were tested. First, the microclimate.

“In the past, other research had found what the microclimate had been in one layer,” said Gu. “Now, with another layer on top, what will change? We looked at the microclimate inside and measured the air humidity and temperature. We also measured the soil temperature, especially if the soil is covered in a plastic mulch bed versus a bare soil bed.”

Then, the production side. How would the plants develop in either type of high tunnel?  What would the yield look like and what would be the fruit quality?

“We have Dr. Jianmei Yu from the Department of Family and Consumer Sciences working on this,” said Gu. “Her team is looking at what modification with the covers on top will happen to the fruit quality of tomatoes. She’s looking at the vitamin C content, sugar, all those indicators of quality.”

And finally, the economics. 

“With an added layer, you’re definitely going to add more cost to it,” said Gu. “You have to have more capital to begin with. Plus, do you have electricity or some other type of power to the motor so the two layers can inflate. For that reason, you need to ask: will the production compensate the extra costs you have?”

A team led by Kenrett Jefferson-Moore, Ph.D., chair of the Department of Agribusiness, Applied Economics and Agriscience Education, is researching the economic viability of single -versus – double-layer covering by looking at the production potential, yield and market price of tomato production, as well as the cost of labor and material for both tunnels. The expected results are intended to help inform small and low-income farmers in an already highly competitive market.

As to the question of whether single- or double-layers are needed, Gu says, for right now, research indicates farmers in the Southern region and the Piedmont Triad can get by with one layer. At the same time, an extra layer can have its benefits.

“For example, in our region, we have heavy snow during the winter,” Gu explained. “Two layers can better combat that. We also have a lot of strong winds in the East Coast region, which two layers can better fight against. Both have pros and cons, of course.”

Outreach and education have also been vital to assisting farmers in making their decision. Workshops, field days, tours, Extension publications, as well as a demonstration site at the Center for Environmental Farming Systems (CEFS) in Goldsboro that replicates A&T’s research, have allowed those interested in purchasing and growing inside a high tunnel to be informed of their options.

“We have different types, different structures, different heights. We’ll definitely be able to know which high tunnel will be able to fit their needs on their farm,” said Gu.

In August 2021, Extension published “High Tunnel Farming,”an instruction guide that offers eight chapters of information ranging from the construction and maintenance of high tunnels to crop choices, soil health and planting by season in North Carolina climate.

2022 marks the last year of research into this project, Gu said; next year, he’ll turn his attention to studying different types of shade in the tunnels to combat rising temperatures due to climate change.

“This year, it’s been so hot and became hot so quickly,” said Gu. “The plants inside the high tunnel can suffer from heat, like humans. Climate change is affecting this. We’d like to use different types, maybe 20 to 30 percent of shade, that will reduce the light coming into the high tunnels and hopefully reduce the heat shock and stress on the plants.”

Gu also said that he’d like to expand research into different perennial plants such as blackberries, raspberries, and blueberries.

Among other projects integrated with the high tunnel study is research into alternative crop opportunities like ethnic vegetables.

“When you think about the big cities in North Carolina, especially in the Research Triangle area, there’s a large ethnic population and many people are moving in,” said Gu. “For example, for me, we eat winter melon, bitter melon, luffa, and some specialty melon. But where can you buy them? You can’t buy fresh ones. There are some Asian grocery stores, but those have been shipped from California or Florida or New York. It’s not fresh and you don’t know where they’re coming from.”

Gu says the growing number of Asian, African and other ethnic populations in metropolitan areas offer an untapped and often overlooked market potential for farmers – both English and non-English speaking – as well as American consumers.

“They’re good stuff!” said Gu of the specialty vegetables. “They’re healthy stuff. They have a lot of potential. Other states have projects going on in this area already, but most are looking at field production. We’re looking at both field and high tunnel, and we can definitely see the benefits of the high tunnel.”