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).