Growers use high tunnels (HTs) specifically to create environments near their crops that would be unavailable otherwise. Those environments can be very beneficial but difficult to achieve and maintain during many cropping periods. This article summarizes key observations about the challenges and opportunities presented to growers when setting the ventilation status of their HT(s).

HTs are essentially square or rectangular boxes with sides, ends, and, occasionally, tops that can be closed or partially to fully opened. The combined relative positions of a HT’s sidewall curtains, end wall doors, and end wall and/or ridge vents (if present) comprise its ventilation status. Farming inside this box, HT growers must use its ventilation status to manage key conditions inside it (e.g., temperature, relative humidity, air movement/exchange). This process is the HT grower’s opportunity and challenge. Setting the ventilation status is an opportunity because it allows the grower to respond to changing external conditions in their attempt to maintain target conditions inside the HT. Setting the ventilation status is difficult because it can demand large amounts of time, energy, and other resources and create questions and stress.

For example, while many vents operate automatically on temperature-sensitive pistons or controls, they generally do not take wind, rain, or other factors that may influence the grower’s interests into account. Also, very important, opening and closing end wall doors and sidewall curtains is typically done manually. Dynamic weather conditions and specific crop needs may then require repeated trips to the HT(s) to change ventilation status, robbing time and energy from other activities and costing fuel, etc. Further, once at the HT(s), there is the question as to what the ventilation status should be. Answering that question can be very difficult. Consider that the relative positions of two sidewall curtains and two sets of end wall doors represents eighty-one combinations at 0%, 50%, and 100% open for each (3x3x3x3=81) and a more realistic use of these four options at five positions each represents 625 combinations. Adding two end wall vents at three positions each to this list brings the total number of possible ventilation status positions to 5,625 (625x3x3). When growers consider tunnel compass orientation, outdoor temperature, wind speed and direction, sunlight and cloud cover levels, crop needs, that relatively small differences in ventilation status can have large effects on conditions inside the HT (e.g., https://u.osu.edu/vegnetnews/2023/02/11/efficient-and-effective-management-of-high-tunnel-environments-1-the-need-and-challenge/), and other factors, selecting the most sensible ventilation status understandably becomes important and potentially difficult.

Some growers simplify by setting a “compromise” status at some point each day or night and moving on, unable or unwilling to change the ventilation status more frequently and, thereby, possibly exposing crops to non-optimal conditions as outside conditions change. Stress created by that scenario has been clear to me in conversations with growers and it appears to be increasing as weather patterns become more dynamic and extreme.

We partner with growers, the research-extension community, and members of industry to improve growers’ success and efficiency at managing conditions inside their HTs, especially through setting their ventilation status. Participation in the Ohio Controlled Environment Agricultural Center and local to international professional working groups and recent support from the USDA-Ohio Department of Agriculture Specialty Crop Block Grant Competition (“Advancing High Tunnel Production: Research-based Support and Technologies to Speed and Enhance Grower Success”) assist in that process. Please contact Matt Kleinhenz (kleinhenz.1@osu.edu; 330.263.3810) for more information.

Growers use high tunnels (HTs) specifically to create environments near their crops that would be unavailable otherwise. Those environments can be very beneficial but difficult to achieve and maintain during many cropping periods. This article summarizes three key observations about monitoring and managing HT environments gleaned from farmers, researchers, and year-round experience with multiple high tunnels at the research station in Wooster, OH since 2003.

1. Change is constant. As many experienced HT users know and new users discover quickly, HT environments can fluctuate a lot over short (minutes-hours) and longer (days-weeks) periods of time, especially during spring and fall. These fluctuations arise from natural conditions outside the HT and the HT user’s management of the structure. Regardless, severe or repeated fluctuations may disrupt crop development and/or lower crop yield and/or quality.

2. Multiple steps and tactics are needed to achieve desired outcomes. Positioning sidewalls, doors, and vents based on external conditions, crop needs, and other factors is the most common approach to managing these fluctuations and maintaining target air temperature, relative humidity, and other conditions in the HT. Actively heating the air and/or soil, shading the HT, circulating air inside the HT with fans, and other steps are also sometimes used. While some HT growers heat air in the HT, especially early in tomato production, fewer appear to monitor HT soil temperature, which also influences crop development and yield potential. Temperatures shown in the graph below are from unheated HTs and they make us wonder about the impact of heating air in a HT on soil temperature. Note that soil temperatures reached optimal levels long after planting.

More research is needed to determine the effect of heating air in HTs on soil temperature, given that most HTs are surrounded by cold soil, experience short, sometimes cloudy days, and are irrigated with cold water in late winter/early spring. Some of these dynamics are depicted in the drawing below.

3. HT environments respond to management, but in incompletely understood ways. Most commercial HTs, especially single bay ones, are rectangles (longer than wide) while multi-bay HTs may approach being square in shape. Regardless, inside, crops differ in height, timing, density, environmental requirements, and position relative to an end- or sidewall. This increases the importance of managing temperature and other conditions in the HT using specific combinations of door and sidewall position, perhaps especially for single bay HTs.

We work to help HT growers be more efficient and effective at managing their HT environments. Our approach involves interlocking steps. For example, we continuously record environmental conditions inside and outside of many HTs along with the positions of their endwalls, sidewalls, and vents. Next, we examine relationships among the: a) external conditions, b) sidewall, endwall, and vent positions, and c) internal conditions. Then, we analyze the status of those three factors alongside cropping outcomes (yield and quality). The overall approach is depicted in the graphic below. In time, we are optimistic this approach will help HT users predict and manage HT environments and crops more effectively.

Finally, weather in Wooster, OH on February 11, 2023, was clear, cold, and calm — ideal for illustrating messages outlined above. Note below how temperatures inside five high tunnels tracked sunlight, outside temperature, and endwall position. Even small differences in the amount one endwall was open influenced internal temperatures. Two important lessons can be taken from the numbers. First, similarly small changes in the position of another end- or sidewall are likely to have much larger effects on internal conditions. Second, effects of small differences in internal conditions created by small changes in ventilation status are likely to be cumulative. That is, relatively small differences in temperature like shown below on any given day are less important than those same differences repeated day after day and season after season. Since those cumulative differences are mostly set by growers’ approaches and management options, enhancing those approaches and options is key. Future articles in this series will focus on those topics. Contact Matt Kleinhenz (kleinhenz.1@osu.edu; 330.263.3810) for more information.

Environmental Conditions In and Immediately Outside Five High Tunnels in Wooster, OH on 2/11/23.

*, ** sunrise and sunset in Wooster, OH on Feb 11, 2023 occurred at 7:37 AM and 5:57 PM, respectively.

Note 1. All high tunnels are single-layer, gothic-shaped, unheated, and located at https://www.google.com/maps/@40.7739922,-81.9150824,574m/data=!3m1!1e3?hl=en. HTs 1 and 2 are 30 ft w x 80 ft long and oriented with their long axis east-west. HTs 3, 4, and 5 are 21 ft w x 48 ft long and oriented with their long axis north-south. All HTs have 2 sliding doors measuring 4 ft w x 8 ft h. When both doors are fully open, the opening created is 8 ft w x 8 ft h.
Note 2. During the time period above, all HTs (doors, sidewalls, vents) are closed unless indicated by a “vent note” below.
A. Sidewalls, doors, and vents closed until 9:51 AM. At 9:51 AM, east end doors open 2 ft (of 8).
B. Sidewalls, doors, and vents closed until 9:51 AM. At 9:55 AM, east end doors open 4ft (of 8).
C. Sidewalls and doors closed. At 10:14 AM, 16-ft² opening in sidewall at SE corner at endwall-sidewall junction closed (small section of plastic had been released at top of sidewall by camlock failure during recent windstorm).
D. Sidewalls and doors closed until 10:02 AM. At 10:02 AM, north end doors open 4ft (of 8).
E. Sidewalls and doors closed until 12:42 PM. At 12:45 PM, north end doors open 4ft (of 8).
F. Sidewall and door positions unchanged 10:02 AM – 12:45 PM. At 12:45 PM, north end doors reduced to open 2 ft (of 8).

The International Fresh Produce Association (https://www.freshproduce.com/) was formed in January 2022 to “speak with a unified, authoritative voice, demonstrate its relevance to the world at large, advocate for members’ interests, and unleash a new understanding of fresh produce.” IFPA advocates, connects, and guides to enhance the prosperity of its members. IFPA membership is large and diverse and IFPA actions and resources can affect and inform growers of all types.

Dr. Max Teplitski is an OSU graduate and the Chief Science Officer of the IFPA. Dr. Chieri Kubota of HCS (https://hcs.osu.edu/) and the OSU Controlled Environment Agriculture Center (https://ohceac.osu.edu/) arranged for Dr. Teplitski to visit with OSU faculty and administration on Nov 4th. He also delivered a presentation outlining research expected to help ensure a sustainable future for the fresh produce industry. Areas of research he outlined were informed by intense evaluation of consumer groups and various trends across the U.S., Europe, and other locations.

Dr. Teplitski highlighted data and information that help explain current and emerging consumer interests. Like growers, the IFPA is interested in what is selling now and what is most likely to sell later. With that in mind, Dr. Teplitski’s summary included many important take-home messages for growers and others, but two messages will be emphasized here. First, recent analysis by IFPA and its partners revealed that consumers cited product quality, price, and nutritional value as their top three considerations when purchasing fresh fruits and vegetables. Interestingly, sustainability-related factors such as environmental impact or recyclable or reusable packaging showed up as consumer demands but not drivers of their purchases. In this analysis, consumers appeared to indicate: (a) that they assume growers and others are operating in a sustainability-driven framework, so (b) focus on other considerations, including quality, price, and nutritional value. This does not reduce the potential importance of sustainability-related factors. In fact, it may signal that consumers expect them to be an industry standard – i.e., in place before consumers begin to separate products based on their other characteristics. Growers may be helped in adjusting to this development by, for example, retailers that look to preferentially source produce from suppliers who use integrated pest management and other sustainability-oriented approaches.

A second message that stood out in Dr. Teplitski’s presentation related to: (a) the increasing consumer acceptance of novel (e.g., tasteful, colorful, pest/disease and stress resistant) varieties developed through bioengineering and gene editing and (b) technologies and systems that enhance the digitization of the industry. Growers familiar with the initial introduction of “GMO” fruits and vegetables years ago may recall their relatively weak acceptance in many markets. The pendulum has not swung entirely toward acceptance. However, use and presentation (labeling) of these genetic technologies is improving, and consumer acceptance appears to be following. This trend has the potential to benefit growers, consumers, and others. Further strategic digitization will have the same impacts. Fruit and vegetable production is a numbers-driven business throughout the value chain, from input supplies and farms to plates. Having and being able to integrate and use key weather, soil, crop, market, and other data will impact day to day and season to season practices.

Stay tuned to updates from IFPA and other member-led organizations working on behalf of their members, consumers, researchers and educators, and others.

Crop yield and quality can be maximized through properly manipulating or managing environmental conditions inside the high tunnel (e.g., light, temperature, relative humidity, and wind in addition to soil moisture, fertility, and other key variables). Temperature, relative humidity, and air movement inside the high tunnel follow conditions outside it and the position (open to closed) of the end-walls, sidewalls, and vents, which are set by the grower. Research underway in Wooster and on the farms of grower-cooperators is designed to minimize the guesswork associated with knowing just what the ventilation status of a high tunnel should be at any one time to achieve the desired cropping outcomes.

One study involves testing the impacts of “kneewalls,” which are sections of plastic installed behind approximately two-thirds of each sidewall for the fall through spring period. Most high tunnel sidewalls roll up to open. When ventilating fall through spring (e.g., to reduce temperature and/or relative humidity and/or increase carbon dioxide levels), opening standard sidewalls can expose crops or seedlings directly to cold air or wind and lower soil temperature, which is also undesirable. We suspect these problems can be mitigated by using kneewalls. We have experimented with them informally on a limited basis for four years and have been excited by our observations. We will soon begin rigorous, comprehensive assessments of the effects of kneewalls on crops and soils.

That effort is part of a much larger examination of relationships among: (a) outside weather conditions (light temperature, wind), (b) high tunnel ventilation status (sidewall and endwall position), (c) air and soil temperatures and relative humidity level inside the high tunnel, and (d) crop yield and quality and soil status.

This effort is starting with our recording data on those variables every five minutes in multiple high tunnels on a continuous basis; our current pace is approximately 130,000 measurements every thirty days in each high tunnel. This approach and pace are essential to achieving our goal of helping growers and others by clarifying relationships among the weather conditions, ventilation status, conditions inside the high tunnel, and crop and soil variables. Findings may reinforce some of what is commonly thought about those relationships and challenge other commonly popular ideas. We are optimistic that, ultimately, what is learned through the work will save growers time, money, and headaches … i.e., will help them be more successful. Stay tuned and contact us if you would like to participate in this research!

Beginning about now and lasting through mid-April, I am often asked by high tunnel tomato growers why their crop is not developing as rapidly as they expect. Troubleshooting covers a wide range of possible explanations. As various ones are considered and ruled out, the possibility they have overlooked the role of soil temperature becomes more important. The high tunnel may be heated, and the crop may have been irrigated and fertilized aggressively, but there is usually no record of the soil temperature, which greenhouse growers know is very important and work to optimize. After all, root growth significantly influences shoot growth and root growth is influenced by soil or root zone temperature.

In my view, we know far too little about soil temperatures in high tunnels — what the optimal ones are at any time and how to achieve them. Still, discussing this with people in Ohio and other states and having done some research on the topic, I was asked to summarize findings at the recent Mid-Atlantic Fruit and Vegetable Convention in Hershey PA (https://www.pvga.org/wp-content/uploads/2022/01/Mid-Atlantic-Convention-Program-22-website.pdf). The subject of the presentation was “root zone heating and root zone temperatures for high tunnel growers” and what follows are a few messages from that presentation.

Root systems are rarely seen but their size, form, and function influence every aspect of the crop, including the size of the canopy and crop marketable yield and profit potential.

Root systems are hard-wired to follow general patterns as they develop. However, conditions surrounding root systems influence their development significantly. Further, those conditions include temperature and are partially set by the grower. So, growers are partially responsible for root system development and function. While a “strong” canopy is good evidence of an equally strong root system, without another canopy to compare it to, it is difficult to be sure it is as strong and productive as it could be. This indicates that a little on-farm experimentation can go a long way in helping optimize total crop management. It also reminds us that since we usually cannot see roots while experimenting or farming, we often need to rely on tracking factors we can measure and that are known to influence root system development and function.

Research findings suggest that tomato growth and production tend to be greatest at root zone temperatures of 65-70 degrees F. This begs two questions.

First, are root zone temperatures in your high tunnel in the optimal range as often as possible? Do you measure soil and irrigation water temperatures? We have recorded soil temperatures every fifteen minutes for various entire seasons in high tunnels and open fields at OSU-Wooster/OARDC and some of the data are shown below (click to enlarge, if needed). Notice the description of the situation in which the readings were taken and when soil temperature readings were in the optimal range. These readings may or may not represent your farm or crops. However, the data may give clues as to the potential temperatures in your fields and high tunnels and encourage you to record those temperatures directly. Reliable, easy to use, inexpensive instruments are available for doing that.

About irrigation water – much of it draws from wells and surface sources and can be very cold (from the crop’s perspective) fall through spring. Although it has not been tested to my knowledge, passing well, surface, or municipal water through drip lines in a high tunnel, heated or not, may be unable to bring its temperature to 65-70 deg F. So, irrigation in the earliest part of the season may amount to bathing roots in water well below the optimal temperature for tomato and other crops and heating the air may overcome that issue only partially.

This brings us to Question 2. Are you convinced that your returns on investments in high tunnel heating, especially of the air for early season tomato production, are as high as possible? If the air temperature is high but soil temperature is low, are you getting as much from the relatively short photoperiods as you could? In early spring, crops may be more limited by a lack of sunlight than below-optimal air temperatures (and excessive heating during extended low-light periods may be counterproductive). We cannot change daylength or cloud cover, but we have some control over air and soil temperatures and may benefit from bringing investments in them into alignment with daylength. For example, should heating increase with daylength? What is the return on investment in aggressive air heating when daylength is very short soon after transplanting?

Addressing those questions opens doors to exploring the relative value of investments in air, soil, or combined heating. That is a subject for other discussions and articles, but it is worth asking if investments in air heating are returning as much as we expect based on the air temperature alone. The 11/6/21 issue of VegNet included an article on root and air heating in fall-time high tunnel leafy vegetable production (https://u.osu.edu/vegnetnews/2021/11/06/soil-heating-effects-on-days-to-harvest-quality-and-regrowth-of-three-high-tunnel-and-fall-grown-vegetable-crops/) and our previous research included spring season experiments, too. Individual crops respond differently to air and soil temperature due to biology and other reasons. For example, the growing tip of lettuce plants is closer to the soil surface than the growing tip of tomato plants and, therefore, may be more strongly impacted by root zone temperature and heating over brief periods.

The point here is that investments in high tunnel heating may be most effective when taking the whole cropping cycle and rotation into account. High tunnel management systems, including temperature, can be designed around one or a set of crops – i.e., around optimizing income from one crop or across the year. Of course, this would occur on a farm by farm, market by market basis. This spring and season, as you are able, consider taking a moment to examine your high tunnel temperature management practices and ask if they maximize your entire annual profit potential.

Grower interest in fall-to-spring marketing of crops freshly harvested from high tunnels is increasing, along with the number and types of questions they have about the production side of the process. Excellent resources and information are available on major aspects (e.g., crop selection, planting schedules) but growers continue to seek and test cost-effective steps to enhance yield and/or quality. Managing temperatures near the crop so they maximize yield and quality has become a major focus for some. We say “temperatures” because root-zone and above-ground temperatures are often different and influence crop development and composition differently. So, we have been studying the effects of common production materials and strategies used to alter temperatures near the crop for many years. Experiments have included various combinations of row covers (film, fabric) to increase air temperatures (primarily) and soil heating. The most recent experiment was started in September and is described in the five panels below. Please contact us (Matt Kleinhenz; kleinhenz.1@osu.edu; 330.263.3810) if you would like more information, have questions about your production methods, and/or would like to discuss collaborative research that could be completed on your farm.

An increasing number of growers look to harvest and market vegetables grown in high tunnels fall to spring. Selling freshly harvested material (e.g., leafy, root, and other crops) from roughly October through April appeals to some farmers but it also raises many production-related questions in practice. Many of these questions relate to the use of plastic films, fabric row covers, and supplemental heating (including of the root zone). Questions such as which ones to use, when, for how long, under what conditions, and in what combination are common. The Vegetable Production Systems Lab has completed research in this area for more than fifteen years, cooperating with farmers often and using high tunnels at OARDC in Wooster which range in size, approach (conventional, organic; flat ground, raised beds), and other characteristics. Findings from these experiments have been summarized in publications (including VegNet) and during programs around the Eastern U.S. Our newest experiment was initiated on Sept 23 and includes the 20 wood-framed raised beds shown here, each seeded to either Scarlet Nantes carrot, Outredgeous lettuce, or Ovation greens (Brassica) mix from Johnnys Selected Seeds. This experiment will examine the influence of daily (8 am – 5 pm) root zone heating (accomplished with electric cables placed approx. 7 inches below the soil surface) in combination with vented plastic film row cover on crop development, yield, and quality. Vented plastic film covers all twenty plots (beds) while daily root zone heating occurs in ten of the twenty plots. Root zone heating will be discontinued at six weeks after seeding but the film will remain in place through final harvest in December. These treatments were chosen partly because two findings have been common in previous research. First, crops (e.g., lettuce, Brassica greens, carrot) and varieties have responded very differently to the use of film, fabric, and root zone heating — whether used alone or in various combinations. The same trend appears to be underway given the relative sizes of the crops shown in the pictures below (taken 10/9/21; carrot at top, Ovation Brassica mix in middle, lettuce at bottom). Second, in this experiment, we are very interested in root zone heating as a supplement to the above-ground heating that occurs with film in place and is typically pronounced September to early November and late January through March. Finally, temperature and relative humidity are recorded in each plot every five minutes, allowing us to describe treatment effects on these conditions very reliably. The sensor unit shown in the bottom-most picture below also relays the temperature and relative humidity readings to the “cloud,” allowing us to see the numbers in near real-time. This battery- and solar-powered Hobolink monitoring and reporting system from Onset Computer Corporation has been in place for more than two years and has greatly enhanced the efficiency and effectiveness of our high tunnel ventilation management across the ten tunnels in our program.

Hundreds of new, promising, numbered (unnamed) potato genotypes are evaluated at research station and farm sites each year. Ohio State is one of many institutions involved. In 2021, we are evaluating more than 100 numbered selections from four breeding programs against seven standard industry varieties. The same evaluation techniques we use can be employed by individual vegetable farms.

High-performing varieties are just one of the core raw materials for vegetable production, which also relies on water, mined or manufactured inputs and equipment, and the know-how to use all of them. Whether formal or informal, variety evaluation is essential for individual growers and the vegetable industry. Since now is when differences among varieties of individual crops begin to show themselves on farms and research stations, it’s a good time to discuss traits and processes used to evaluate varieties.

When we evaluate genotypes of potato being considered for naming and release as varieties, we score plant maturity and record total and marketable yield and more than ten tuber characteristics for each entry (e.g., tuber size and shape, skin color and texture, flesh color, eye depth, incidence of internal defects, and specific gravity and chip color). Collaborators in other states evaluate the same genotypes for pest and disease resistance, crop tolerance to heat stress, storage effects on tuber quality, and tuber cooking quality and sensory properties. So, like for other vegetables, developing potato varieties requires teamwork.

Background on the Variety Development Process

Experimental genotypes originate in public-sector breeding programs based at universities and the USDA. In fact, although varieties developed by private companies (e.g., major processors) contribute significantly, the U.S. potato industry (especially the fresh/tablestock and chip sectors) has long relied on varieties developed in the public sector. Public-sector varieties are developed by large teams led by universities, USDA, and/or state industry associations or organizations and account for most of the available varieties, acreage, and value of production.

Whether public or private, variety development teams include breeders/geneticists, agronomists/horticulturalists, plant pathologists, entomologists, food scientists, farmers, processors, and people with expertise in related areas.

Potato varieties are named, released, and made available for commercial use only after years of comprehensive, widespread testing, beginning with just a few plants and concluding at farm scale. Once released, varieties support processing (i.e., chip, fry), fresh market/tablestock, and/or breeding programs. The varieties ‘Atlantic’ (released in 1976), ‘Dark Red Norland’ (1957), ‘Katahdin’ (1932), ‘Kennebec’ (1948), ‘Red LaSoda’ (1953), ‘Superior’ (1962), and ‘Yukon Gold’ (1981) are just a few examples of public-sector varieties that have been planted to many thousands of acres over decades of production. Varieties like these set the bar for and/or are found in the “family trees” of newer, increasingly popular varieties.

Still, markets, production conditions, and industry factors change continuously. Therefore, variety development must be ongoing and once-popular varieties are eventually displaced by new, more farmer-, processor-, and consumer-friendly ones. The process is designed to enhance industry success and consumer satisfaction.

Evaluation is nearly continuous since sites are located throughout the U.S. and the process begins before planting and ends long after harvest. Groups based in the East, Midwest/Upper Midwest, West and Pacific Northwest, and South often coordinate the work. Ohio State and Ohio farmers and processors have participated annually for more than fifty years. We emphasize the evaluation of genotypes originating in eight breeding programs and with potential value in fresh and chip markets and have contributed to the release of multiple varieties used in Ohio and elsewhere.

Sharing Results

Data from our 2021 trials will be summarized in a report available at https://u.osu.edu/vegprolab/technical-reports/ with data from 2020 and previous years available at https://neproject.medius.re/trials/potato/ne1731 and https://neproject.medius.re/. Later, we will join team members from Maine, New York, Pennsylvania, North Carolina, Virginia, Florida, and USDA and industry partners to discuss evaluation outcomes and begin selecting new entries and others to be evaluated again or dropped from the program. With information reflecting variety or experimental selection performance in the field and on the plate, the breeder and team have key information when making the thumb-up/thumb-down decision on each entry.

Still, for all crops, the performance of each variety (or experimental genotype) hinges on how it is managed, the know-how allowing growers to get the most from each variety. Planting and harvest dates, plant populations (spacings), irrigation and fertility programs, etc. influence variety performance and, therefore, whether a grower will select the variety again. So far, potato genotype evaluations at Ohio State have been completed without irrigation and this approach has clearly affected tuber yield and quality. We are rethinking this approach and look forward to speaking with vegetable and potato growers about their use of irrigation.