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Home HortTechnology Three Diverse Microclimates Used in Study of Organic Lettuce Production Systems
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Three Diverse Microclimates Used in Study of Organic Lettuce Production SystemsLUBBOCK, TX—High tunnels are large, framed structures with no electrical or ventilation systems and covered with greenhouse-grade plastic. Typically used to produce high-value horticultural and agricultural specialty crops like lettuce and leafy greens, high tunnels can provide climate protection during severe weather conditions and extend growing seasons. Interest in high tunnels is burgeoning among specialty crop growers in the Unites States, due in part to access to new technologies, interest in local food production, and the availability of more federal funds.

Depending on growing location, lettuce production may be limited during early spring and summer months because of unfavorable temperatures that increase the risk of "bolting" (premature production of flowering stems), tip burn, and leaf bitterness. A new study from a team of researchers from Texas, Tennessee, and Washington provides lettuce growers with significant information for extending their production seasons. The team compared six spring-planted lettuce cultivars for yield and quality when grown in high tunnels or open-field production systems located in three diverse U.S. regions where high tunnel lettuce production has not been commonly used.

According to the study's corresponding author Russ Wallace from the Texas A&M Agri-Life Research and Extension Center in Lubbock, the growing locations were chosen for their contrasting climates: Knoxville (TN) is characterized as hot and humid, Lubbock (TX) as hot and dry, and Mount Vernon (WA) as cool and humid. The high tunnel models were selected for each location based on general climatic factors and grower preferences; six commercial lettuce cultivars were selected based on specific characteristics necessary for improved lettuce quality production in southern regions. The experiments showed that in southern climates like Knoxville and Lubbock, high tunnels allow for earlier lettuce production during periods when the risk of freeze, wind damage, or both may occur. "In the maritime Pacific climate at Mount Vernon (WA), higher temperatures and greater growing degree days (GDD) accumulation in high tunnels decreased the time to harvest by only 1 or 2 days; therefore, the economic profitability of high tunnel use for lettuce in that region needs careful consideration," Wallace said.

"Winter and early spring lettuce production using high tunnels in southern regions may potentially mitigate physical/adverse risks associated with planting early open-field crops," the study’s authors said. "The cooler temperatures typical of earlier plantings in high tunnels allow for improved lettuce quality and yield. Earlier plantings inside high tunnels may reduce the risk of premature bolting, but further research is needed at these locations to determine best planting dates and practices."

The scientists noted that the use of high tunnels may be particularly advantageous in climates similar to the Texas High Plains, where high winds and blowing dust are common in the spring, but cautioned that the type of high tunnel used in these climates should be carefully selected to avoid structural damage.

They concluded that high tunnels can be effective for protecting the crop from severe or adverse weather common in open-field production in all three climates and provide beneficial alternatives for lettuce growers interested in extending the growing season.



The complete study and abstract are available on the ASHS HortTechnology electronic journal web site:

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at


Original Article:

Lettuce Yield and Quality When Grown in High Tunnel and Open-Field Production Systems Under Three Diverse Climates
Russell W. Wallace, Annette L. Wszelaki, Carol A. Miles, Jeremy S. Cowan, Jeffrey Martin, Jonathan Roozen, Babette Gundersen, and Debra A. Inglis
HortTechnology 22:659–668. [Abstract][Full Text][PDF]

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