Establishing benchmarks likely to increase growers’ profitability

University of Vermont Extension Professor Vern Grubinger summarized the results of research to address the economics of high tunnel production that he and his research colleague, UVM Assistant Professor Becky Maden, initiated in 2024, at the 2025 High Tunnel Production Conference in West Lebanon, NH.

“The take-home message is that good records and a detailed budget are needed to accurately assess costs and returns (revenues) from growing high-tunnel tomatoes, as there are many steps involved,” Grubinger said.

“Though some budget templates exist, we are working with growers to test a highly detailed budget, collect their results and eventually use that data to establish benchmarks that describe typical ranges of some indicators of profitability, such as yield per square feet, net revenues per square foot and pounds of production per minute of labor.”

His presentation explains that the 2024 high tunnel tomato “benchmarking” survey included 47 growers, all of whom had three or more years’ experience as tunnel tomato growers and two-thirds of whom manage using organic practices.

The range of comparative results in yield were startling. The top 10 yielding tunnels of the growers (all who completed their data records) showed a big difference: an impressive average of 3.5 lbs./sq. ft. vs. an average of 1.8 lbs./sq. ft. in the remaining number. That whopping 94% difference in yield translates into a very significant dollar difference in growers’ gross revenue.

Grubinger and Maden recently had the results of their collaborative work published in “HortTechnology,” an open-access, online-only publication of the American Society for Horticultural Science.

“The adoption of one or more key practices could lead to improved yield on many farms growing high tunnel tomatoes,” the authors concluded. “These practices (that fall into three areas) include: optimizing plant density, drip line density and passive ventilation openings; adding automated ventilation, air and ground heating systems and horizontal air flow fans (HAF); and using grafted plants and the long-term high tunnel soil test.

“Economic returns on the adoption of practices depend on the management capacity of farmers and the revenue generated by additional tomato production. To evaluate the impact of new practices, growers need to accurately measure yield.”

Two UNH Extension field specialists – Jonathan Ebba, based in Strafford County, and Heather Bryant, based in Grafton County – teamed up to talk about “Environmental Control: Managing Heat, Air & Humidity.”

Bryant is in the early stages of planning a retrofit of the 20-year-old research-focused high tunnel near her county Extension office.

“I had two colleagues come to our office to visit the tunnel and then brainstorm on how to proceed,” she explained. “I visited with vendors who sell both high tunnel kits and monitoring equipment to learn more about my options. I often discuss with my clients what they like about their tunnels as well as any upgrades they’ve installed.”

This early-stage process, Bryant said, means she’s very aware of what upgrades are now available. Through her job, she’s very aware of regional environmental changes, including hotter, humid summers and drought.

Airflow within a high tunnel is very important, she said, since it not only moves heat around but also humidity (moisture). This, surprisingly, even applies to small pockets of air around leaves. Equalizing carbon dioxide is also important, since it’s vital for photosynthesis.

An online USDA-NRCS bulletin, “Controlling the High Tunnel Environment,” includes an example of the need to balance the heat load with cooling so plants do not become stressed.

“For instance, tomatoes grow best at 70º to 75º and have a maximum air temperature of 85º,” the bulletin states. “Temperatures much higher than 85º (day) and 75º (night) can stress tomato cultivars and result in flower abortion, pollen sterility and ripening disorders. In addition to the increased heat load on plants, warm air holds more moisture and disease problems can occur above 85% relative humidity. The grower must manage the high tunnel environment to provide optimal growing conditions for their crops while minimizing disease.”

The team cautioned growers to be aware that both calcium (Ca) and boron (B) are transported in most plants through their own structures. Low airflow and high humidity can lead to deficiencies, adversely affecting new growth and fruiting.

by Edith Tucker