Winter Production of Leafy Greens in the Southwestern USA using High Tunnels

Final Report for SW09-041

Project Type: Research and Education
Funds awarded in 2009: $193,879.00
Projected End Date: 12/31/2013
Region: Western
State: New Mexico
Principal Investigator:
Dr. Steven Guldan
New Mexico State University
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Project Information


We evaluated three high tunnel designs of various heat retention capacities (single layer [SL], double layer [DL] and DL plus a water heat sink [DL+B]) across different climatic zones in the Southwest for their potential to profitably produce winter greens. Lettuce and spinach were planted in fall in AZ, CO and NM. Results demonstrate that high tunnels in combination with row cover can provide adequate winter protection for greens, and the DL+B design produced the highest daily air and soil temperature minimums. An economic analysis indicates that the SL and DL designs had the highest probabilities of producing positive returns.

Project Objectives:

1) To quantify the differences between three passive-solar high tunnel designs of different expense and heat-retention capacities (SL, DL and DL+B designs) to assess their potential to provide a suitable environment for winter production of leafy greens.

2) To evaluate growth and yield of one spinach and one lettuce cultivar at three planting dates (on or near October 25, November 20 and December 15) within each tunnel.

3) To conduct economic analyses to determine the probability of producing positive returns in each tunnel design, planting date and crop scenario.

4) To distribute results and recommendations to farmers, researchers, extension educators and other agriculture personnel in NM, CO and AZ.


Farmers in much of the southwestern U.S. are under pressure to divert agricultural land and water to residential development and other non-agricultural uses. However, increased urban populations can help keep farmers in business by increasing direct- and local-marketing opportunities. For example, the Santa Fe Farmers’ Market is open all year, including the winter months, but farmers who can produce year round are needed. Other marketing options, such as Farm-to-School in New Mexico, encourage and assist schools and other public institutions to purchase from local farmers. However, to develop and take advantage of these markets, farmers must be able to reliably and cost-effectively produce a product during the late fall, winter (December, January and February) and early spring months. Although institutions may be interested in purchasing locally, it is often not feasible for them to have contracts that only deliver produce during the normal growing season, especially in climates with relatively short seasons. Lack of affordable methods for winter production are limiting local and other marketing options, enterprise diversity and profits.

At the start of this project in 2009, most research in the U.S. on crop production in high tunnels was taking place in the northeastern and mid-Atlantic states including Pennsylvania (Lamont et al., 2003; Orzolek et al., 2004), New Jersey (Both et al., 2007) and Connecticut (Gent, 2005). In the intervening period, many more published studies have been released, including other geographical regions (numerous authors: HortTechnology 19:1, 2009). Although the purpose of using high tunnels is to modify the environment for enhanced crop production, the capacity to do so using passive-solar designs will vary greatly from one agro-climatic zone to another. No research was found in the literature on high tunnel production in the geographic region covered by this project.

In much of the Southwest, most winter days are sunny, but nights are below freezing. The high number of sunny days provides an ideal environment for winter high tunnel production, provided that cost-effective production systems are developed. Significant to the importance of water conservation in the semiarid southwestern U.S., crops grown in high tunnels during the cool time of year have high water use efficiency, due in large part to moisture being retained in the high tunnel structures compared to open air production.

The interest in high tunnel production in the Southwest region is high, and the Alcalde extension specialist on this project has received many requests in the past ten years from producers to assist them in constructing and using low-cost high tunnels for season extension. With his direction, a number of high tunnels have been constructed using simple and low-cost designs that use a single layer of 6-mil polyethylene plastic covering treated with a UV inhibitor (Jimenez et al., 2005). They are useful in increasing daytime temperatures to accelerate plant growth for earlier production, and for some frost-tolerant crops, to keep them producing later in the fall. However, heat captured during the day is largely lost at night as it re-radiates out of the tunnel through the single-layer plastic covering. Therefore, there was a great need for research on and demonstration of relatively inexpensive high tunnels that allow for production during the coldest months of the year, and thus allow more producers to enter new markets. A detailed characterization of different tunnel designs and their capacity to modify the winter growing environment were also needed in southern and northern sections of the region, as recommendations can vary depending on winter temperature regimes.

High tunnel design options, such as double-layer plastic coverings and inside water storage features, can increase the capacity of the tunnel to retain heat even as the outside temperature drops during the night. However, light is reduced during the winter months, and a double-layer of plastic can further reduce the quantity of light intercepted by the crop. In addition, using double-layer plastic or water storage in a tunnel increases start-up costs, so we determined the risk and probability of positive returns for each tunnel design, crop and planting date combination.

This project evaluated three basic designs of high tunnels (single layer of plastic [SL], double layer [DL] and a double layer with barrels as a water heat sink [DL+B]) for winter production of leafy greens. Our emphasis was on low-cost, practical structures that are applicable to limited resource producers – the great majority of our producer clientele. A replicated study of the capacity of these three different tunnels to alter the growing environment was carried out at Alcalde, NM, representing a northern and colder location in our region, and at Las Cruces, NM, representing a southern and warmer part of the region. Several producer and cooperator institution sites evaluated one DL tunnel each and provided critical producer input on the effectiveness and practicality of high tunnel production during the winter (coldest months of the year) and allowed testing of high tunnel production among the broad range of agro-climatic zones present in the region.

The economics of winter production of two leafy crops (lettuce and spinach) in high tunnels in two locations in New Mexico were investigated, first using a simulation analysis in which yields were stochastic variables, followed by a sensitivity analysis to examine returns from the high tunnel designs more closely. The returns examined in the sensitivity analysis were net of high tunnel materials, crop seed cost and electricity. Combining the risk and the sensitivity analyses provides growers with a unique evaluation process to make high tunnel design, planting date and crop choices.

Because only a limited number of species, varieties and planting dates could be tested within the tunnels, air (all tunnels) and soil (Alcalde and Las Cruces) temperature data were collected both inside and outside of the tunnels. These temperature data expanded the usefulness of the study by providing important baseline data that can be used to describe the potential of the tunnels to support the establishment and/or growth of other types of crops from late fall through winter.

To distribute project results to producers, students, county agents and other agricultural professionals, we offered numerous workshops, field days and individual visits to these sites located across the region.


Click linked name(s) to expand/collapse or show everyone's info
  • Jeff Anderson
  • Tomas Apodaca
  • Ian Chamberlain
  • Connie Falk
  • Jeff Graham
  • Del Jimenez
  • Beth LaShell
  • Benita Litson
  • Jim Maiorano
  • Gerald Moore
  • Darrin Parmenter
  • Manoj Shukla
  • Mark Uchanski
  • Tony Valdez
  • Joran Viers


Materials and methods:

Objective 1:

At both NMSU-Alcalde (northern location) and NMSU-Las Cruces (southern location), all three tunnel designs were constructed. At each cooperator site, one DL (see description below) tunnel design was constructed. Below are the basic plans of three walk-in high tunnel designs; 16 feet by 32 feet in size:

--Single Layer (SL): single layer of heavyweight woven polyethylene plastic (SOLAROOF 172, J&M Industries; Ponchatoula, LA) for tunnel exterior;

--Double Layer (DL): one layer of lightweight woven plastic (SOLAROOF 140; interior), followed by a second layer of heavyweight plastic (SOLAROOF 172, exterior) and inflated with a fan;

--Double Layer plus Barrels (DL+B): double layer of woven polyethylene plastic for tunnel exterior plus 16 55-gallon black metal barrels filled with water to act as a heat sink.

Each high tunnel design was replicated twice at each research station location for a total of six tunnels per location. Tunnel frames were constructed principally of two-inch PVC pipe, with three-foot side walls made primarily of wooden 4x4 posts and 2x4s. Tunnel design and required materials were a modification of that described by Jimenez et al. (2005). All research station tunnels, and on-farm tunnels when possible, were oriented such that the length ran east-west for maximum solar interception. Sixteen 55-gallon metal drum barrels were painted with non-reflective black spray paint and filled with water. These barrels were aligned on the north side of each of the DL+B tunnels to minimize shading of the crop. The six high tunnels were clustered at each location, with tunnels adjacent north to south spaced at least 35 feet apart to prevent shading in the low winter sun.

Two data loggers (Hobo U12-008 4 Channel External Data Logger, Onset Computer Corporation; Bourne, MA) were mounted to stakes or 4x4 posts inside each high tunnel. Loggers were programmed to record temperature every 30 minutes, 24 hours per day from October-March. One data logger was placed in the center of the tunnel, and one was placed in the southwest corner. Data logger probes (air/water/soil temperature sensor six foot cable TMC6-HD, Onset Computer Corporation; Bourne, MA) were placed in six locations in and around each high tunnel, three inches below the soil surface to record soil temperatures and 12 inches above the soil surface to record air temperatures. Soil temperature probes were buried horizontally outside each tunnel, inside under a floating (non-supported) row cover (Agribon AG-19, J&M Industries; Ponchatoula, LA), and inside but not under row cover. This floating row cover was left on the plots continuously after the second planting dates, except for harvest and plot maintenance. Air temperature probes were also placed outside each tunnel, inside under row cover, and inside not under row cover. Air temperature sensors were inserted vertically into solar radiation shields that were mounted to wooden or metal stakes. Data was downloaded from the loggers at least once per year using HOBOware Pro software (Version, 2002-2009, Onset Computer Corporation; Bourne, MA).

Photosynthetically active radiation (PAR) was measured each season within one month of the winter solstice, December 21. Measurements were taken in six locations around each tunnel: outside the tunnel, inside the tunnel in the center walkway, inside the tunnel on the north bed, inside the tunnel on the south bed, inside the tunnel on the north bed and under the row cover, and inside the tunnel on the south bed and under the row cover. At Las Cruces, PAR was measured with an LP-80 Accupar PAR/LAI Ceptometer (Decagon Devices, Inc.; Pullman, WA) and at Alcalde PAR was measured with a LightScout Quantum Meter (Spectrum Technologies, Inc.; Plainfield, IL). Both devices were leveled prior to taking readings and PAR was recorded in micromoles per square meter per second (µmol•m-2•s-1).

Objective 2:

In year one, lettuce (‘Flashy Trout Back’) and spinach (‘Long Standing Bloomsdale’) were planted in separate plots on November 24-25 and December 15-17 at both locations. In years two and three, the December planting window was abandoned and an October date was added. In seasons two and three the first planting occurred October 27-29, and the second planting occurred November 17-19. Plots were hand-seeded and manually weeded as needed. Standard yield (fresh and dry weights of marketable product), plant height and stand count were measured. Plants were harvested multiple times as “cut and come again,” allowing for one to five harvests/winter depending on the location and season. At Alcalde and Las Cruces, individual plots were two feet x five feet. Within plots, three rows (north-south orientation) of each crop were planted eight inches apart. Harvest data were collected from the center three feet of the center row. At producer and cooperator sites, exact plot size and row direction varied based on the particular management constraints of each location.

Fertilization and pest issues were managed using organic principles and amendments. Irrigation at Alcalde and Las Cruces varied and included hand application, overhead sprinklers and drip irrigation lines. Irrigation at on-farm and other cooperator sites included drip and manual watering.

Objective 3:

The economics of winter production of lettuce and spinach in high tunnels were investigated, first using a simulation analysis in which yields were stochastic variables, followed by a sensitivity analysis to examine returns from the high tunnel designs more closely. The returns examined in the sensitivity analysis were net of high tunnel materials, crop seed cost and electricity. A range of prices ($2-6/lb) was obtained during the harvest season from Mountain View Cooperative, a retail outlet in Las Cruces, and from La Montanita Co-op, a locally owned chain of four retail food cooperatives headquartered in Albuquerque, NM. Sensitivity analyses were conducted to estimate gross returns to growers given a range of prices and yields that encompassed the prices and yields relevant to the SL and DL tunnel designs and two crops. These two particular designs were studied more closely after the simulation analysis results indicated they were likely the two most viable tunnel design options.

Objective 4:

Results have been dispersed by research and extension publications, press releases, conference presentations, workshops and field days, and in the classroom. Further details are provided in Publications/Outreach, below.

Producer and University/College Cooperator Sites:

At most producer and cooperator sites, the same four treatments (two greens x two planting dates) were replicated at least four times in a RCBD within each tunnel. Any resulting free space in each tunnel was made available so that producers could experiment with other crops and management, particularly in years two and three based on the capacity of the tunnel on their site to alter winter growing conditions in year one. Crop yield and temperature data were also collected as for the Alcalde and Las Cruces research station locations.

Research results and discussion:

Objective 1:

Maximum air and soil temperatures in each design were rarely significantly different from each other. However, the DL+B design had consistently lower estimates, which indicates a buffering effect due to the thermal mass of the water barrels (Figures 1-2). Daily air and soil temperature minimums were highest in the DL+B design, again due to the buffering effect of the water barrels. The SL design had the lowest air and soil minimum temperatures, which was consistent with the original design hypothesis. For examples of these temperature regimes, please see Figures 1-2. Representative temperature graphs of two collaborator sites in Tijeras, NM and Window Rock, AZ can be found in Figures 3-4.

PAR levels were significantly higher in the SL design, except in Alcalde during seasons 2 and 3. This may be explained by dust accumulation, abrasion from wind storms, and aging of the plastic. Giacomelli et al. (1990) found that after four years, PAR transmission through polyethylene film was reduced by 7% due to age. In the present study, the amount of PAR transmission in a DL high tunnel was comparable to the PAR transmission in a SL tunnel. Even with the reduction in PAR, light was likely not limiting for crop growth.

Collection of this type of detailed environmental data is critical for our deeper understanding of covering types for these increasingly common season extension structures. At two cooperator sites, heavy snowfall caused partial or total collapse of the tunnel. In high snowfall areas growers might consider using smooth plastic as snow can tend to stick to the rougher surface of the woven plastic.

Objective 2:

Our original research hypothesis was that an earlier planting date would produce the highest yields of winter-produced leafy greens. The second hypothesis stated that the tunnel design with the highest heat retention capacity (DL+B) would produce the greatest yield. Results from this study show that the earlier planting date did produce a higher season-long yield, and that planting early was especially critical in the colder climate of Alcalde, NM (Table 1). In regards to the second hypothesis, the SL and DL designs produced comparable yields to the DL+B in most scenarios.

Although planting date differences were significant in most analyses, in season 1 in Alcalde, planting date differences for November and December were not evident. In Las Cruces, however, the November planting date yielded significantly more lettuce and spinach than the December planting date (Table 1). The warmer temperatures in November in Las Cruces may have led to better plant establishment before the coldest months of the year (December-January) set in. By November in Alcalde, it may have been too cold for significant plant growth to occur. In seasons 2 and 3 when the planting dates were changed to October and November, significant planting date differences were found in Alcalde. In season 2 in Las Cruces, the October and November planting date differences were also evident.

Fewer harvests were possible in Alcalde (3) than in Las Cruces (5) because of lower winter temperatures, which impacted total season-long yield. Lettuce and spinach produced similar yields in this study, but we observed that during the coldest nights of the year (0 F or lower) minor tip freeze damage occurred in the lettuce but not in the spinach. This might be a consideration for crop choice for winter production in the region.

The original study hypothesis stated that the high tunnel design with the highest heat retaining capacity (DL+B) would produce the greatest yield. However, maximum temperature ranges were not considered as a source of crop stress during the winter months. Since the tunnels were not ventilated, maximum air temperatures in the SL and DL design tunnels exceeded the air temperature thresholds for lettuce and spinach (>75°F), especially in the month of March (Figures 1-2). Maximum air and soil temperatures in each design were rarely significantly different from each other. However, the DL+B design had consistently lower estimates, which indicates a buffering effect from the thermal mass of the water barrels.

Construction and salinity problems in the first and third seasons in Las Cruces hindered crop growth, which prevented additional replication of the three-design analysis in southern New Mexico. In order to avoid salinity problems, a watering system that does not allow a high evaporation rate and a water source that is low in dissolved salts is recommended for the arid southwest.

From these results we feel that passively heated high tunnels can contribute greatly to winter production of leafy greens in the arid southwest. High tunnel leafy green production could contribute to the supply of locally grown produce and extend the growing season for small farmers.

Objective 3:

Reported under Economic Analysis.

Objective 4:

Reported under Publications/Outreach.


Both, A.J., E. Reiss, J.F. Sudal, K.E. Holmstrom, C.A. Wyenandt, W.L. Kline, and S.A. Garrison. 2007. Evaluation of a manual energy curtain for tomato production in high tunnels. HortTechnology 17(4):467-472.

Gent, M.P.N. 2005. Effect of genotype, fertilization, and season on free amino acids in leaves of salad greens grown in high tunnels. Journal of Plant Nutrition 28:1103-1116.

Giacomelli, G.A., K.C. Ting, and W. Fang. 1990. Wavelength specific transmission of polyethylene film greenhouse glazing. Proc. 22nd Natl. Agr. Plastics Congr. p. 129-134.

HortTechnology 19(1):23-65. Various authors. High Tunnels: season-extending technology.

Jimenez, D., R. Walser, and R. Torres. 2005. Hoop house construction for New Mexico: 12-ft. x 40-ft. hoop house. New Mexico State University, Cooperative Extension Service. Circular 606.

Lamont, W.J., Jr., M.D. Orzolek, E.J. Holcomb, K. Demchak, E. Burkhart, L. White, and B. Dye. 2003. Production system for horticultural crops grown in the Penn State high tunnel. HortTechnology 13(2):358-362.

Orzolek, M.D., W.J., Lamont, and L. White. 2004. Promising horticultural crops for production in high tunnels in the mid-Atlantic area of the United States. In A.P. Papadopoulos (ed.) Proceedings of the XXVI International Horticultural Congress: Protected Cultivation 2002: In Search of Structures, Systems and Plant Materials for Sustainable Greenhouse Production, Toronto, Canada. 11-17 August, 2002. Acta Hort. 633.

Research conclusions:

Through the high tunnel construction workshops carried out across New Mexico, in northeast Arizona and in southwest Colorado, more than 200 individuals received hands-on training regarding assembly of high tunnels made of wood, PVC and plastic. General parts lists and costs were made available, as well as information on other factors to consider (essential tools, etc.) when building their own high tunnel or hoop house. A major impact was the number of people who learned what is involved in building a high tunnel by attending these construction workshops. The goal was to teach attendees how to construct a similar tunnel.

Through knowledge gained in constructing and using the design of high tunnels built for this study, construction recommendations were refined and applied by extension specialist Del Jimenez when constructing about 70 additional high tunnels in workshops requested by producers. In addition to more workshops in New Mexico, Colorado, and Arizona, some of these additional workshops took place in Wyoming and Washington.

Although there has been great interest in high tunnels in the Southwest, there was limited research available upon which to base recommendations or offer guidance. This project demonstrates that on sunny, yet cold and short, winter days, daytime temperatures inside the high tunnels and under row cover were at least 20-30 degrees F higher than outside, and about 10-15 degrees F warmer at night. Results from this project will assist producers to select the type of passive solar structure suited to their budgets and winter growing environment. Spinach and lettuce production and economic analyses results will assist growers in determining the likelihood of producing positive returns when growing greens for harvest during the coldest time of the year (December-February). Temperature data within three designs of high tunnels during winter will also assist growers to determine the capacity of these structures to provide a winter growing environment for other crop species.

A desired long-term outcome of this project is that a significant number of producers in the region will be engaged in winter greens production. This production can begin to fill market potential and serve as a catalyst for new contracts, leading to greater diversity and profitability in agriculture, and thus sustain farmers and agricultural lands. In addition, consumers in the region will have access to fresh local produce for most or all of the year.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Extension publications:

Walker, S., M.E. Uchanski, and D. Jimenez. 2012. Hoop house vegetable production. New Mexico State Univ. Coop. Ext. Serv., Las Cruces, Guide H-252. <>

Edwards, J., and D. Jimenez. 2013. Hard-sided high tunnel construction. Univ. of Wyoming Coop. Ext. Serv., Laramie, B-1240.


Enfield, J.S. 2012. Winter production of leafy greens in the southwestern USA using high tunnels. New Mexico State Univ., Las Cruces, MS Thesis.

Hecher, E.A. Dos Santos. 2012. The economics of high tunnels for season extension in the Southwestern U.S. New Mexico State Univ., Las Cruces, MS Thesis.

Research papers:

Hecher, E.A., C.L. Falk, J. Enfield, S.J. Guldan, and M.E. Uchanski. 2013. The economics of low cost high tunnels for winter vegetable production in the southwestern United States. HortTechnology (accepted, in revision).

Uchanski, M.E., C.L. Falk, S.J. Guldan, M. Shukla, D.M. VanLeeuwen, and J. Enfield. 2013. Crop environment characterization in winter high tunnels in the southwestern United States. HortScience (in preparation).

Uchanski, M.E., C.L. Falk, S.J. Guldan, M. Shukla, D.M. VanLeeuwen, and J. Enfield. 2013. Growth and yield of leafy greens during winter in high tunnels in the southwestern United States. HortScience (in preparation).

Research meeting presentations:

Hecher, E., C.L. Falk, M.E. Uchanski, and S.J. Guldan. 2012. The economics of high tunnels for season extension in the Southwestern US. Selected paper, Western Economic Association International, San Francisco, CA, August, 2012.

Enfield, E. and M.E. Uchanski. 2012. Winter production of leafy greens in New Mexico using high tunnels. HortScience 47(9): S252-S253.  Poster presentation at the American Society of Horticultural Sciences (ASHS) annual meeting in Miami, FL.

High tunnel construction workshops:

Construction of project high tunnels began September 2009. Eighteen high tunnels were constructed: seven near Las Cruces, NM, one near Tijeras, NM, six at Alcalde, NM, one near Window Rock, AZ (but on New Mexico side of border), one at Dine College, AZ, and two near Durango, CO. High tunnel construction workshops were held at all sites and were open to the public. Students also attended and assisted in construction at these events at NMSU-Las Cruces and Dine College. These workshops were led by Del Jimenez and organized in cooperation with county agents and other project PIs and cooperators, and provided to attendees hands-on experience in constructing 16x32-foot high tunnels.

As mentioned in previous section, demand for high tunnel construction workshops has continued with Del Jimenez carrying out about 25 per year since the initial 18 in the first year of this project. On average, about 25 people participate in each hands-on construction workshop.

Field Days:

--Construction and crop production aspects presented at Alcalde Science Center Field Day, Alcalde, NM, August 11, 2010.
--Winter field day illustrating winter crop growth at Alcalde, NM, January 19, 2012.
--Winter field day illustrating winter crop growth near Durango, CO, February 2, 2012.
--Winter field day illustrating winter crop growth near Tsaile, AZ, February 7, 2012.
--Winter field day illustrating winter crop growth near Las Cruces, NM, February 23, 2012.
--Construction and crop production aspects presented at Alcalde Science Center Field Day, Alcalde, NM, August 15, 2012.
-- Construction and crop production aspects presented at Leyendecker Plant Science Center Centennial Field Day, Las Cruces, NM, August 2012.

News articles, press releases, and videos (incomplete list):

NMSU website:


New Mexico Organic Farming Conference- A major impact during the second and third year of this project was sharing study results with farmers at the New Mexico Organic Farming Conference held in Albuquerque, NM. A 1.5-hour presentation was made at the conference on February 19, 2011, and another presentation was made at the Conference on February 17, 2012. These presentations introduced the research and shared preliminary data with the southwest organic farming community.

Other presentations/tours:

The project has been presented to over 25 groups and several individuals who visited the Alcalde Science Center, in addition to being part of other presentations on Alcalde Center research given at local meetings. The Leyendecker Plant Science Center hosted several groups of visiting farmers from around the region and conducted tours as appropriate.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

--More planting and harvesting date options and combinations for winter production;

--Conventional and organic pest control options (for example, aphids can be a particular problem in high tunnels during winter months);

--Soil salt accumulation with low quality irrigation water;

--Winter crops other than lettuce and spinach;

--The utility of adding additional structural reinforcements to high tunnels, such as concrete footings and purlins of adequate strength; structural reinforcement costs and benefits;

--High tunnel ventilation options to avoid heat stress of the crop during sunny and warm days.


We wish to acknowledge Western SARE for the economic support that made this important project possible. Additional salaries and research support were provided by state and federal funds appropriated to the New Mexico Agricultural Experiment Station. The authors acknowledge the technical assistance of Mr. Mike Petersen, Ms. Victoria Frietze, Ms. Luz Hernandez, Mr. David Archuleta, Mr. David Salazar and Mr. Val Archuleta.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.