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 are below freezing. Therefore, passive-solar high tunnels should be 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 in November and/or December at eight study sites in Arizona, Colorado and New Mexico that reflect a range of climatic zones. Yields and tunnel temperatures were collected in most tunnels during year 1 (2009/2010). At three sites, structures were damaged from heavy snowfalls. These tunnels will be repaired to withstand greater snow loads.

Objectives/Performance Targets

A) To quantify the differences between three passive-solar high tunnel designs of different expense and heat-retention capacities (high, medium and low-end models) in order 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 variety at two planting dates (November 10 and December 15) 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 New Mexico, Colorado and Arizona.

Accomplishments/Milestones

We began construction of project high tunnels in September 2009. Eighteen high tunnels or “hoop houses” 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. Due to manufacturing errors in the hoop house plastic shipments, there were delays in completing hoop house construction by the time of the first planned planting date (early November); planting on or near the second planned planting date occurred at most hoop house sites. Some cooperator sites also began experimenting with other planting dates and varieties, as encouraged in the grant proposal. Temperature probes and data loggers were installed in all locations. Hoop house 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 field days were led by Del Jimenez and organized in cooperation with county agents and other project PIs and cooperators and provided attendees hands-on experience in constructing 16-foot x 32-foot hoop houses.

A Master of Science student in NMSU’s Department of Plant and Environmental Sciences, Juliette Enfield, began her graduate studies in January 2010 and will continue with the project until its completion. Juliette has compiled 2009/2010 data and has begun the environmental and biological analysis (temperature, light, yield, plant growth, etc.) for all sites. A new graduate student (M.S.) in Agricultural Economics, Emmanuel Hecher, began on the hoop house project in August 2010. During the fall 2009 construction of the hoop houses, materials costs, labor inputs and volunteer hours were recorded. Harvest labor times were recorded during data collection in early spring 2010. This data will be used for a full economic analysis as part of Mr. Hecher’s graduate studies at New Mexico State University.

Preliminary results indicate that on sunny, yet cold and short, winter days, daytime temperatures inside the hoop houses were at least 20-30 degrees higher than outside. At Alcalde, the hoop houses with double layer plastic plus the heat storage feature (black barrels filled with water) appeared to maintain higher temperatures inside at night compared to the single layer plastic hoop houses. This resulted in substantially higher yields for the two crops in the high-end (double layer of plastic and black barrels) as compared to the low end model (single layer of plastic) (see Figure 1).

Lettuce and spinach germination was successful at most sites. Although plants developed normally, growth was understandably slow, especially given the particularly cold weather that occurred during late December and early January in the region. One of the Colorado sites experimented with planting as early as October 9, 2009 and taking a harvest before a heavy snowstorm collapsed the PVC hoops of the structure in early December 2009. After removing the snow from the roof, vertical reinforcements were placed in the tunnel and will be worked into the design/repair for the next season. The collaborator in this location noted that the earlier the crop was planted, the sooner it germinated and vice versa (eight days to germination for crops planted October 9 vs. 22 days to germination for crops planted on November 30). Yields were highest in November and December harvest dates but were negligible in January and February. Harvests resumed the following spring in March. This break in harvest was due to cold winter temperatures in the single layer plastic hoop house. A second layer of plastic will be added for the 2010-2011 season.

At Tijeras, NM, and one Arizona site, structures were also seriously damaged from heavy snowfalls; these tunnels will also be repaired to withstand greater snow loads next season. The hoop house on the certified organic vegetable farm near Las Cruces, NM (Fairacres, NM -owner Jeff Graham) did not experience any significant snow accumulation and harvested both lettuce and spinach in February and March (see Figure 2). Even with a single layer of plastic, spinach and lettuce yields were good and three “cut and come again” harvests were conducted. Insects became an issue for the spinach crop in this location, significantly reducing yields.

Although the woven plastic that we decided to use is strong, it apparently does not allow snow to slide off of it easily, which caused excessive weight stress on the structures at the high snowfall sites. Currently, a second layer of plastic is being added to each of these sites, and we will use the more standard and smoother six mil plastic to help shed snow.

Data collection and analyses will continue for two more winter seasons. Presentation of the project took place at the 2010 Field Day of the Alcalde Science Center, which occurred on August 11, 2010, with an attendance registration of 236. The press release announcing this field day also highlighted and discussed the winter greens project. Presentation of the project will continue to take place at field days and for tour groups.

• Figure 1. Crop yields from three different models (high, medium, and low) of hoop houses planted with two crops (lettuce and spinach) in Alcalde, NM. Yields are combined 72 feet of row for each crop.
• Figure 2. Yields of two crops (lettuce and spinach) for on-farm collaborator, Jeff Graham, in Fairacres, NM. Yields are combined 12 feet of row for each crop.

Impacts and Contributions/Outcomes

Through the high tunnel construction workshops carried out across New Mexico, in northeast Arizona and in southwest Colorado, more than 136 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 and legislators. However, no publications have been produced at this early stage in the project.

The major impact during the first year of the project was the number of people who learned what is involved in building a high tunnel by attending the construction workshops. The goal was to teach attendees how to construct a similar tunnel. We are aware of four construction workshop volunteers who constructed hoop houses on their farms after having attended a workshop.

Long-term outcome:

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 that will 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 fresh local produce available for most or all of the year.

• Figure 4. Volunteers install the second layer of woven plastic that will be inflated with a small circulation fan during winter production. Las Cruces, NM. July, 2010.
• Figure 5. Soil and air temperature probe placement inside the hoop houses and amongst the spinach and lettuce crop in Alcalde, NM. February, 2010.
• Figure 3. Student volunteers learn construction techniques for high tunnels in Las Cruces, NM. September, 2009.

Collaborators: