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

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

Summary

In much of the Southwest, most winter days are sunny, but nights can fall below freezing. Therefore, passive-solar high tunnels (synonym: hoop houses) are ideally suited to this region. We are evaluating high tunnels across different climatic zones for their potential to profitably produce winter greens. Lettuce and spinach were planted late October and mid-November in Alcalde (northern location) and Las Cruces (southern location), New Mexico. Lettuce and spinach were also planted at on-farm study sites in Arizona (AZ), Colorado (CO) and New Mexico (NM). Participants from on-farm study sites provided experiential information about the use of high tunnels for winter production. Yields and tunnel temperatures were collected in all operational tunnels during three winter seasons. Data collection and analyses will continue for one more winter season (2012-2013) at the southern experiment station due to poor stands in year three. Four winter field days were held at four cooperator and/or experiment station locations in early 2012. In addition, two summer field days held at each of the experiment stations highlighted this research.

Objectives/Performance Targets

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

B) To evaluate growth and yield of one spinach and one lettuce cultivar at two planting dates within each tunnel.

C) To conduct economic analyses to determine relative profitability of each tunnel design.

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

Accomplishments/Milestones

Eighteen high tunnels or “hoop houses” were constructed in 2009: seven near Las Cruces, NM, one near Tijeras, NM, six at Alcalde, NM, one near Window Rock, AZ, one at Dine College, AZ, and two near Durango, CO. Hoop house construction workshops were held at these sites and were open to the public. These workshops were led by Del Jimenez and organized in cooperation with county agents and other project PIs and cooperators. They provided attendees hands-on experience in constructing 16 x 32-foot hoop houses. The hoop houses at Window Rock, AZ, and at Tijeras, NM were seriously damaged in 2009-2010 due to heavy snowfall during the winter. These two houses were repaired in 2010 and slightly modified to better withstand snowfall, including an outer layer of snow shedding plastic and internal frame reinforcements. Cooperating producers continued experimenting with planting dates and plant varieties, as encouraged in the grant proposal. Temperature probes and data loggers were installed in all locations. A presentation of the hoop house study’s preliminary findings was also given at the New Mexico Organic Farming Conference in Albuquerque in February 2011 and 2012.

A Master of Science student in New Mexico State University’s Department of Plant and Environmental Sciences, Juliette Enfield, has compiled the harvest and temperature data over the past three seasons and has begun the environmental and biological analysis (temperature, light, yield, plant growth, etc.) for all sites. During the construction of the hoop houses, materials costs and labor inputs were recorded. These data, in addition to maintenance costs and harvest yields, were used for an economic analysis as part of Emmanuel Hecher’s graduate studies at NMSU. Mr. Hecher, a Master of Science student in the Agricultural Economics Department, also worked closely with the cooperating producers on the project to gather survey information about the economic uses of their hoop houses.

For objective A of this study, the differences between the three designs of hoop houses are being examined for their potential to provide a suitable environment for leafy greens during the coldest months of the year. There are two replicated study locations, Alcalde, NM, and Las Cruces, NM. Each study location has a total of six hoop houses with two of each design. The three designs include a single layer of plastic (SL), a double layer of plastic (DL) and a double layer of plastic with water barrels (DL+B). Preliminary temperature data analysis shows that each hoop house model has a different temperature regime as seen in Figures 1, 2 and 3. The DL+B house had a maximum and minimum temperature range that was closer to the optimum temperature for lettuce growth than the other hoop house models. During the coldest part of the day, the DL+B hoop house was, on average, about 10 degrees Fahrenheit warmer than the single layer hoop house. The thermal mass of the water barrels in this model buffers the temperature extremes in the hoop house by slowing temperate change. This effect was seen at both experiment locations (Alcalde and Las Cruces). However, the DL+B hoop houses did not have the highest yields in Las Cruces, as seen in figures 4 and 5. This result was unexpected and is currently being investigated. Due to low yields in the first season of the project, especially for lettuce and spinach planted in December, an earlier planting date was used in years two and three. This earlier planting date allowed the seeds to germinate and develop faster during longer days and slightly warmer temperatures. As seen in figures 4 and 5, the lettuce and spinach that was planted in October yielded more than the crop planted in November. Harvest was terminated when the crop quality declined due to temperature and maturity of the plants (late Febuary 2011).

Many producers planted at different dates than specified and included site specific crops. The producer near Window Rock, AZ and all other collaborating producers had a DL model hoop house. The DL model hoop house retains heat well during the day, but the air temperature at night only stays slightly warmer than outside temperatures (Figure 6). Future hoop house models will require a venting system to avoid the high temperatures that are far from the optimum growth temperature range. The temperature differential during the day is quite large for the outside vs. inside temperatures, which is expected on a sunny day. The continued challenge is to keep that heat during the night when these temperatures come back together again. The use of row cover in the hoop house as a protective covering for the crop raised the minimum temperature inside the hoop house on average five degrees (Figure 7). During the particularly cold event in early February 2011, the outside temperature at Window Rock was -10F (lethal for lettuce and spinach in most situations), inside the hoop house was 0F, and under the row cover was +15F, a 25 degree difference (Figures 6 and 7). The producer in Window Rock, AZ also noted that the soil retained more moisture if the row cover was doubled in thickness when applied over the crop. We will continue to solicit producer inputs and observations from season three.

• Figure 3. Maximum and minimum air temperatures inside three different models of hoop house (SL, DL, DL+B) in Alcalde, NM, during the winter growing season (2010-2011). Temperatures are average of 2 replications for each model of hoop house.
• Figure 4. Total season long crop yields from ‘Bloomsdale’ spinach planted in October and in November in three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM. Yields are combined 180 feet of row for each crop.
• Figure 5. Total season long crop yields from ‘Trout’s Back’ lettuce planted in October and in November in three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM. Yields are combined 180 feet of row for each crop.
• Figure 6. Comparison of daily high and low air temperatures inside vs. outside the hoop house in Window Rock, AZ, during the winter growing season (2010-2011).
• Figure 7. Comparison of daily high and low air temperatures inside the hoop house vs. inside the hoop house under row cover in Window Rock, AZ, during the winter growing season (2010-2011).
• Figure 1. Maximum and minimum air temperatures inside three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM, during the winter growing season (2010-2011). Temperatures are average of 2 replications for each model of hoop house.
• Figure 2. Maximum and minimum air temperatures inside three different models of hoop house (SL, DL, DL+B) in Las Cruces, NM, during an unusual temperature drop in early February (2010-2011). Temperatures are average of 2 replications for each model of hoop house.

Impacts and Contributions/Outcomes

Through the high tunnel construction workshops carried out across New Mexico, northeast Arizona and southwest Colorado, to-date 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.

The hoop house projects at both Alcalde and Las Cruces, NM have been the subject of numerous tours to visitors, scientists, school groups and legislators. Presentation of the project took place at two regularly featured Field Days at the Alcalde Science Center (August 11, 2010 (236 registered) and August 15, 2012 (188 registered)). The press release announcing the 2010 field day also highlighted and discussed the winter greens project. Since the beginning of 2010, 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. Winter field days were held in 2012 at Alcalde, NM (January 19), Tsaile, AZ (February 7), Las Cruces, NM (February 23) and Durango, CO (February 2) to illustrate growth of the lettuce and spinach during the winter season. One graduate student has successfully defended his thesis project, and the second is preparing to defend in November. The completed thesis undertook a risk analysis of the three hoop house designs by planting date and by crop at both experimental sites, and the other will be a horticultural study on the use of hoop houses for lettuce and spinach production during the winter in the Southwest. Manuscripts from these masters degree theses will be submitted to scientific journals to be published and shared among the scientific community. Through project collaboration with County Extension offices in the Southwest (Rio Arriba, Doña Ana, Tri-State Navajo Nation, Bernalillo, La Plata), the results of the hoop house trials will continue to be shared with farmers through workshops and additional publications.

A major impact during the second and third year of this project has been sharing preliminary 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 provided a forum to introduce the research and share preliminary data with the southwest organic farming community. There was significant attendance and interest in the use of hoop houses for season extension and winter production.

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

• Figure 9. Collaborating producer Ian Chamberlain, in his hoop house in Durango, CO, January 2011.
• Figure 8. Emmanuel Hecher collecting replicated harvest data in Las Cruces, NM, February 2011.

Collaborators: