A 3-year project focused on developing fruit and vegetable systems suited to high tunnel production in the high-elevation arid Intermountain West. Successful systems were developed for lettuce, tomato, squash and strawberry production. Work with brambles showed that methods suited to other regions were not locally appropriate. Results were disseminated to end users through seven Extension bulletins, 10 grower workshops and eight Extension presentations and two in-service trainings (Extension and NRCS). Communication to the scientific community will be carried out through three research presentations and at least four research journal articles that are in the review process or are nearing completion.
- 1) To characterize the effect of high tunnels on crop productivity for a range of vegetables and small fruits grown early and late in the annual crop production cycle.
2) To determine compatible crop rotation strategies under organic production techniques.
3) To compare in-ground to containerized bench-top planting strategies for effectiveness in season extension and labor efficiency.
4) To assess the economic benefits of these different crop sequences and management techniques.
5) To distribute this information to urban and rural farmers and home gardeners of Utah and the Intermountain West at local field days, at extension educational events, and through print and electronic forms.
Utah has over 15,000 farms, more than 85% of which are considered to be very small farms with an average value of sales less than $50,000 per year. Intensive production practices of high value crops are most suited to these farms. Produce can then be sold to the consumer at the farm gate, through local farmers markets, or on a contract basis such as a Community Supported Agriculture (CSA) operation. To maximize output on these small farms, methods are needed to extend the growing season. Season extension increases productivity of available land, and allows for targeting early and late market windows for maximum returns. Two technologies, plastic mulches and fabric row covers, have been used successfully to increase plant growth and yields in many parts of the US. Plastic mulches help speed up early season growth by increasing soil temperature while row covers help increase air temperature around the plant thus offering some protection from the cold. Although plastic mulches and row covers may extend the production season by several weeks, if growing conditions are unfavorable (cold soils, low air temperatures, wet soils), plant establishment and the early growth benefits is lost. Also, neither plastic mulches nor fabric row covers offer significant protection from late spring frosts.
Recent research efforts have focused on growing high value horticultural crops in un-heated or minimally heated plastic greenhouses often called high tunnels. Tunnels allow growers to produce crops well outside the normal production periods for the specific crop and in some cases allow year-round production. Research results for most vegetables indicate that early and late season production of a variety of crops are best as they do not compete in the marketplace with crops grown outdoors. Vegetable crops of interest for early production include tomatoes, peppers, summer squash, cucumbers, and eggplant. In autumn, cool season vegetables like specialty lettuce, herbs, and other green are regularly grown. Fruit crops now being tested in tunnel houses include strawberries, raspberries, and blackberries.
Prior to this project, much of the tunnel research and commercial implementation of this technology have taken place in the Eastern U.S. where sheltering the crops from rain prevents crop damage and can decrease pathogen pressure. The enclosed space also lends itself to integrated pest management practices. These advantages lend themselves to organic management practices and to producing the highest quality product. The high altitude desert climate of the Intermountain West may provide a more favorable climate for high tunnel production due to the intense sunlight and the ability to mitigate the day-night temperature fluctuations that limit plant growth in the spring and fall. In order for growers to exploit this technology, additional research efforts on production strategies for high altitude desert conditions need to be evaluated, and detailed economic information is required to ensure that the systems devised are profitable.
A total of 12 high tunnels were constructed at the Greenville Research Farm in North Logan. Nine of these tunnels are the low-cost PVC-framed style that we designed. The three remaining tunnels are 30’ x 30’ with high sidewalls for growing taller crops such as brambles. A series of studies were carried out in these tunnels over the three year project.
Vegetables: Organic and conventional fertility programs were compared with treatments replicated in four tunnels. Systems were evaluated for early-season and late-season tomatoes and squash, and winter salad greens. In addition to fertility programs, combinations of low tunnels, floating row covers, soil heating cables, and incandescent lights (low cost heat source) were evaluated for further extending the growing season of tomatoes.
Fruits: Strawberries, raspberries and blackberries were established both inside and outside of tunnels to compare production seasons, input requirements, fruit quality, and productivity. Management considerations included “tipping” raspberry canes in an attempt to delay harvest, and using rotating trellises for blackberries to improve winter protection.
Two high tunnels were divided into sections to compare in-ground production to containerized “vertical” growing systems. The vertical system consisted of A-frame tower supports holding PVC rain gutters containing soilless media. The sloping production area formed by these production towers were either one-sided and south facing, or two sided and facing east and west. One house was devoted to winter lettuce production, the other to strawberry production. Treatments within the systems compared planting and harvest dates, as well as soil heating. These treatments were repeated over at least two seasons.
Two containerized systems for raspberry production were compared to in-ground production. The summer-bearing variety ‘Tulameen’ and the fall-bearing variety ‘Caroline’ were established in 7 gallon pots containing soilless media. Pots were either placed on the soil surface, or in buried socket pots in a “pot-in-pot” system. The primary objective of containerized production was to rotate plant types and double crop the tunnel space. Since the three tunnels used for this experiment were “four-season” tunnels, the tunnels were to be used to force early production of the summer bearing varieties, then move these plants to an outdoor holding area and fill the space with fall-bearing plants for a fall crop. The pot-in-pot system has proven effective in Utah’s high light summer conditions to reduce heat load on the root system. Each system had replicate plots with multiple plants in each plot.
Two graduate students were recruited to carry out the research outlined in this project. Daniel Rowley had an undergraduate background in Ag Business and Ag Economics. Britney Hunter had an undergraduate background in Plant Physiology and Horticulture. Daniel was assigned to oversee the fruit-related research projects and to work on developing templates for analyzing the economics of each of the test systems. Britney oversaw the vegetable research and specialized in evaluating low-cost heating strategies. As part of their M.S. theses, both students were required to develop multiple research papers evaluating components of the respective production system and to develop enterprise budgets comparing the economics of each system.
Educational programs and materials – In addition to their research responsibilities, graduate students involved in the is project were required to submit extension bulletins for peer review and publication through USU Extension and to give presentations at grower meetings and field days. The graduate students and PIs in the project also developed a one-day workshop on constructing and managing high tunnels, and developed a powerpoint presentation on high tunnels that was distributed to county Extension staff throughout Utah.
Commercial cooperators – For the project, commercial growers were recruited to participate as cooperators. Although quantitative date from these cooperators was limited, they did provide valuable feedback on the challenge and successes of implementing high tunnel technology under range of climatic and cropping conditions and systems.
- a) Simple protection systems like tunnel-within-tunnel, soil warming with heating cables, and low wattage light bulbs significantly increased soil and air temperatures in the spring thus enhancing early growth of tomato. Tomato harvest began on 7 July 2009, despite an unusually cold wet spring. Tunnel production is usually more than one month earlier than outdoor grown tomatoes in Northern Utah. Early price at the Logan Farmers Market is $2/lb and product sells briskly.
b) Organic production in the tunnels is as productive as, or more productive than conventional (not organic) tunnel production methods for all vegetable crops tested. Our finding showed that in Yr 1, yields were about 25% lower in the organic system as compared to the conventional tunnels. By Yr 2, yields were only 10% less and in the third year, yields were equal to or greater in organic tunnels as compared to conventionally grown vegetables.
c) Annual rotations of tomato-squash-lettuce or squash-tomato-lettuce as spring-fall-winter crops have proven to be highly productive and compatible. Rotations used included late March planted tomatoes (July-mid-August harvest) followed by fall squash (September through October harvest) then winter greens. A second approach was April planted squash (May-June harvest) followed by July planted tomato (September to early November harvest) with late fall planted greens.
d) Extending fall raspberry production with high tunnels appears to be a user-friendly system that has been successful both at the research farm and with cooperating growers in Rich and Utah counties. However, advancing summer-bearing cultivars into early spring has been problematic at both the North Logan and the Utah County location. The primary limitation has been protecting floricanes from the temperature fluctuations that injure flower buds.
e) The summer/fall planted June-bearing strawberry system did not produce a late fall tunnel crop as has been reported for the mid-Atlantic region (Takeda and Newell, 2007) but did produce a very nice spring crop that was 4 to 5 weeks earlier than the field crop. Early strawberries were easily sold for $4.50 per pound, a 50% premium over in-season prices for local fruit.
f) One of the strawberry systems that was evaluated involved late-winter planting of day-neutral cultivars for production of a summer/fall crop. These produced a late spring crop but despite the use of shade cloth, summer cropping was relatively low. However, as the season cooled, production began again. In 2008 production continued until approximately 1 December. In 2009, with supplemental soil heating, flowering and fruiting continued through the winter. While the level of productivity would not justify the cost of added heat inputs, the results suggested that this system could be very promising for fall fruit production. By November of 2008, the plants appeared to be run down despite weekly fertigation. For the 2009 season, part of the tunnel was replanted mid-summer in an effort to increase fall production. Replanting did not significantly boost fall production and plants were again run down by November, likely due to low light levels.
- a) Early fall and late spring lettuce production in raised towers is more productive than ground-based systems. When adding supplemental heating cables to the soil, growth is even greater. Higher plant populations and improved space utilization make these potentially viable systems. Crops can be cycled through the systems in 6-8 weeks depending on time of year. Lower mid-winter production levels are due to light and soil and air temperature limitations.
b) The vertical strawberry growing system improved productivity in the tunnel space. Although yields per tunnel area were increased by the use of gutters, winter injury to the plant roots was extensive. By removing the gutters from the towers, placing them on the ground and covering with row covers during the coldest months, winter injury could be minimized. However, the increased yields did not justify the added cost of constructing and managing the vertical system, even when winter protection was adequate to prevent root injury.
c) The containerized raspberry production system was a failure for multiple reasons. First, winter cane survival was problematic both in the containerized and in-ground systems. The cultivar Tulameen was selected based on recommendations from the high tunnel research program at Cornell University. ‘Tulameen’ is not hardy to Cache Valley and the tunnels did not improve winter cane survival. In fact, late-winter temperature fluctuations likely contributed to more severe cane injury. In addition, plant growth and vigor was poor in the containers for both summer and fall-bearing types. The soilless media was formulated according to recommendations also from Cornell University. The likely reasons for lack of vigor include poor water- and nutrient-holding capacity of the media, and excessive root zone temperatures that were not adequately alleviated by the pot-in-pot method.
Results under these objectives will be reported in a subsequent section.
Grower cooperators were recruited to experiment with high tunnels and provide their feedback. Cooperators were required to build their own tunnels and provide all maintenance and labor. Researchers provided some plant materials for their trials and offered expertise in crop and tunnel management. The experience of commercial grower cooperators was also mixed. Following is a summary of the experiences of grower cooperators for this project, listed by geography.
High Elevation 1: One high elevation cooperator located in the Bear Lake Region was interested in high tunnels to produce fruits and vegetables for a local gardener’s market, but was unable to construct a tunnel in time to participate in the project. An alternate cooperator was recruited that was located approximately 35 miles south of the original cooperator. A high tunnel was constructed over existing fall-bearing raspberries to enhance late fall production. High tunnels were compared to field production areas with and without the use of spring floating row covers. The climate in this region is not typically suitable for fall raspberries as the growing season is too short. Results were as follows:
Yields for Fall 2008:
Field production: 1,260 lbs/acre
Field production with spring row cover: 6,300 lbs/acre
Spring row covers + fall high tunnels: 12,500 lbs/acre
After this season, the tunnel was badly damaged in a wind storm, and the grower chose to lease out his raspberries for the following two seasons to pursue other business opportunities. No further data were available.
High Elevation 2: The second cooperator at a high elevation site experimented with strawberries and vegetables for small-scale truck gardening. Since the tunnel space is limited the cooperator has focused on trying to maximize productivity by double cropping the space. As a result it was determined after one year that strawberries were not an efficient use of space, requiring too much time between planting and harvest. Currently, he is growing carrots, radishes, turnips, spinach, cilantro, onions and broccoli during the early spring. Summer crops are peppers, tomatoes and squash. This is significant not only in the amount of season extension, but in the ability to successfully grow warm season vegetables that is otherwise unsuitable for their production. This cooperator is employed by USU Extension and has also used the tunnel for demonstration and education purposes.
Wasatch Front 1 – Utah County: At the beginning of this project, this cooperator’s business was focused on field production of strawberry for direct-sale fresh market and for some pick-your-own sales. His interest in high tunnels was for early season strawberries and off-season tomato and lettuce production. Shortly after the start of the project, the cooperator built several greenhouses and shifted the emphasis on bedding plant and nursery production. While he initially planted a portion of one house to strawberries for fruit production, he came to the realization that selling potted fruiting strawberry plants was more profitable than selling the fruit, and focused on the new core business of bedding plant sales. His early experience provided some useful information on cultivars, and on vertical growing systems.
Wasatch Front 2a – Utah County: The core business of this cooperator is production of tree fruits (apples, peaches and cherries) for the wholesale markets. He was interested in high tunnel raspberry production as a potential diversification opportunity. A tunnel was constructed and planted to summer and fall-bearing raspberries in containers, based on the best recommendations at the time (Cornell). His results were very similar to ours with winter injury severely limiting his summer crop, and poor vigor in the containers. After three years of very successful fall production following was his conclusion: “The fall varieties. By the time the weather gets cold and it is time to put the plastic up to protect the plants from freezing, I am tired of the darn berries and I am praying that they will freeze. It’s time to move on to next season.”
Wasatch Front 2b – Utah County: A close relative of the Wasatch Front 2 cooperator became interested in high tunnels and constructed two low-cost tunnels to investigate the potential for tomato and strawberry production. The core business of this new cooperator is tree fruit production for wholesale and retail sales, and some agro-tourism. The site selected was relatively windy which presented some problems for the tunnels, and the soil conditions were not well suited to strawberries. Tomato production was very good, but the grower abandoned the effort after one season to focus energy on the core businesses.
Wasatch Front 3a – Davis County: The core business of this cooperator is vegetable production for local direct sales both through on-farm stand and at local farmers markets. He was primarily interested in high tunnels for early tomatoes. As one of our outreach activities, workshop participants built a low-cost high tunnel on his farm at the cooperator’s expense. The following day, he constructed a second high tunnel and both were planted to tomatoes in March of 2009 for early production. In the fall of 2009, the cooperator constructed two additional tunnels, also for tomato production, to better supply the demands for early-season production. The grower reported large consumer demand in 2009 at several of the Salt Lake City farmers markets with sales averaging $4.00/lb.
Wasatch Front 3b – Davis County: The core business of this cooperator is also vegetable and small fruit production for local markets. In 2008, early tomato sales at Salt Lake City and Park City farmer’s markets ranged between $3.50-4.00/lb. Recently they have started growing June-bearing and ever-bearing strawberries in tunnels to complement their early tomato operation.
Low Elevation 1 – Washington County: This cooperator constructed a low-cost high tunnel in order to experiment with small-scale truck farming. The tunnel was initially planted to strawberries. High winds with a prevailing direction perpendicular to the tunnel have made it difficult to keep this tunnel assembled and functioning properly.
Low Elevation 2 – Grand County: This cooperator focuses on production of fruits, vegetables and field crops for local sales. A major focus of the high tunnel has been to extend the season for vegetable production. The grower has been very successful using indeterminate tomatoes and is even using some supplemental heat to further extend the season. Based on the success of the initial tunnel, the grower purchased abandoned greenhouse structures in order to expand his protected-cultivation area.
Not surprisingly, those cooperators that had the most success were those that had extensive experience growing the same crop in the field, and also had established retail outlets for their produce. Those who experimented with new crops or whose pilot projects were too radical of a departure from their core business, struggled to make the system work. In some cases, the best knowledge at the outset of the experiment was clearly not appropriate, and thus doomed their potential for success.
In addition to the presentations and the research and outreach publications resulting from this project (see below), the major outcome of this work has been to develop management guidelines for successfully implementing high tunnel technology into diversified fruit and vegetable production in high elevation arid climates. Methods for tomato, lettuce and strawberry production have been optimized, and economic analysis indicates that these methods can be highly profitable. Perhaps as important as these “successes” are some of the “failures”. Specifically, we have shown that technologies developed in other climates do not translate to the high elevation Intermountain West. For example, the raspberry cultivars and management systems that have been proven successful in the Eastern U.S. are not suited to the Intermountain West. From this we have developed some hypotheses for what might work better, and are currently initiating projects to evaluate these new strategies.
In late 2009, the Natural Resource Conservation Service (NRCS) announced a new pilot project that would provide matching funds for developing high tunnel production on commercial fruit and vegetable farms. This announcement caused a firestorm of interest in climate-appropriate high tunnel technology. As a direct result of this WSARE-funded project, science-based information was available to distribute to interested farmers. Requests for information came from throughout Utah, and from neighboring states including Idaho, Wyoming, Colorado, Nevada and New Mexico.
Educational & Outreach Activities
- Rowley, D. 2010. Season extension of strawberry and raspberry production using high tunnels. M.S. Thesis. Utah State University.
Hunter, B. 2010. High tunnel production of lettuce and tomato. M.S. thesis. Utah State University.
- Rowley, D., B.L. Black, D. Drost and D. Feuz. Early season extension using June-bearing ‘Chandler’ strawberry in high elevation high tunnels. Submitted to HortScience.
Rowley, D., B.L. Black, D. Drost and D. Feuz. Fall strawberry production using day-neutral varieties and high tunnels. In preparation.
Hunter, B.., D. Drost and B.L. Black. Cold temperature protection for early season high tunnel tomatoes. In preparation.
Hunter, B.., D. Drost and B.L. Black. Space utilization for high tunnel lettuce. In preparation.
- (all Extension bulletins are available online at extension.usu.edu/publications; search for high tunnels)
Black, B.L., D. Drost, D. Rowley and R. Heflebower. 2008. Constructing a Low-cost High Tunnel. USU Extension Publication: HG/High Tunnels/2008-01pr.
Rowley, D., B. Black and D. Drost. 2009. Fall-bearing raspberries in high tunnels. USU Extension Publication Horticulture/High Tunnels/2009-01pr.
Rowley, D., B. Black and D. Drost. 2010. High Tunnel Strawberry Production. USU Extension Publication Horticulture/High Tunnels/2010-01pr.
Rowley, D., B. Black and D. Drost. 2010. Strawberry Plug Plant Production. USU Extension Publication Horticulture/High Tunnels/2010-02pr.
Hunter, B., D. Drost and B. Black. 2010. High Tunnel Tomato Production. USU Extension Publication Horticulture/High Tunnels/2010-03pr.
Black, B.L., and D. Drost. Temperature Management in High Tunnels. USU Extension Publication: HG/High Tunnels/2010-03.
Hunter, B., D. Drost and B. Black. 2010. High Tunnel Lettuce Production. In preparation.
- 21 Feb 2008 High tunnel production: Possible and profitable. Half-day workshop presented at the annual Diversified Agriculture Conference. Presentations topics included tunnel design considerations, management considerations and cropping options. The Workshop also included a tour of the Greenville research facility. Logan, UT (27 participants).
11-12 Apr 2008 Constructing and using a low-cost high tunnel. 2-day workshop presented in Sanpete County. USU Extension. Day one presentations were on tunnel design considerations, and on fruit and vegetable cropping options (Presenters: Drost and Black). The second day program involved construction of a tunnel (Drost, Black, Anderson). Ephraim, UT. (50, 25 participants).
4 Nov 2008 High tunnel field day and workshop at the Greenville Research Farm. North Logan, UT. (10 participants). Target audience: Northern Utah Vegetable Growers.
16Mar 2009 Building and managing a low-cost high tunnel for extended-season fruit and vegetable production. Presentations were on off-season berry production (Rowley), temperature effects on high tunnel vegetables (Drost), winter production and low-cost heating options (Hunter), tunnel design considerations and low-cost tunnel construction (Black). The afternoon session involved constructing a tunnel on a commercial farm. Sponsored by USU Extension. Kaysville, and West Layton, UT (32 participants). Target audience: commercial Fruit and Vegetable Growers in the greater Salt Lake Valley.
4 Apr 2009 Building and managing a low-cost high tunnel. Morning session presentations included off-season berry production (Rowley), temperature effects on high tunnel vegetables (Patterson), tunnel design considerations and low-cost tunnel construction (Black). The afternoon session involved a hands-on demonstration of tunnel construction. Sponsored by USU Extension and the Carbon and Emery county Extension offices. Price, UT (24 participants). Target audience: Small farmers and large scale home gardeners.
16 Apr 2009 Building and managing a low-cost high tunnel. Morning session presentations included off-season berry production (Black), high tunnel vegetable production (Heaton), tunnel design considerations and low-cost tunnel construction (Black). The afternoon session involved hands-on construction of a high tunnel for use by the local high. Sponsored by Wayne, Garfield and Piute county Extension offices. Junction, UT (27 participants from Wayne, Piute, Garfield and Iron Counties).
11 Sept 2009 Building and managing a low-cost high tunnel. Presentations were on off-season berry production (Black), temperature effects on high tunnel vegetables (Hunter), winter production and low-cost heating options (Hunter), tunnel design considerations and low-cost tunnel construction (Black). The afternoon session involved hands-on construction of a high tunnel for a market gardener. Sponsored by Weber and Davis county Master Gardeners. Fruit Heights, UT (18 participants).
26 Feb 2010 Building and managing a low-cost high tunnel. A 4-hour workshop with presentations on “Getting the Most from Your Environment” (Drost) and on high tunnel construction methods (Drost). 7th Annual Diversified Agriculture Conference. Vernal, UT. (45 participants). Eight (8) tunnels constructed by participants after the workshop.
15 Apr 2010 Building and managing a low-cost high tunnel. Afternoon session was the hands-on tunnel construction program. Evening presentations were on tunnel designs, tunnel management considerations, and fruit and vegetable cropping options (Drost and Black). Evening sessions presented Sponsored by USU Extension and the Duchesne and Uintah county Extension offices. Mountain Home, UT (18 participants).
26 May 2010 High tunnel construction & season extension. A half-day workshop with presentations on tunnel cropping options, management considerations construction methods (Drost) Workshop at the 2010 Nevada Indian Agriculture & Rural Summit: Agricultural Innovation and Community Sustainability. Fallon, NV. (42 participants, 50% of which were Native American).
- 17 Jan 2008 “Season extension technology for fruit and vegetable production.” Annual conference of the Western Colorado Horticulture Society. Grand Junction, CO. (45 participants)
15 Mar 2008 “High tunnel production, possible and profitable!” Two 30-min presentations made by Britney Hunter (graduate student) to the Pocatello Growers Circle. Pocatello, ID. (40 participants)
6 June 2008 “High tunnels for home gardens.” Presentation made by Britney Hunter (graduate student) to the Utah Master Gardener convention (20 participants).
10 Sept. 2009 “Growing vegetables in high tunnels” – 30-min presentation for Summit and Wasatch county master gardeners (15 participants)
23 Apr 2010 “Gardening with high tunnels” – Two 1-hour presentations made by graduate student Britney Hunter. Richfield, UT. (15 participants)
26 April 2010 “High Tunnels for High Elevations: Integration into High Schools.” Presentation to Rehoboth Christian School Development Board. Rehoboth, New Mexico. (8 participants). Navajo School.
2 June 2010 High tunnel gardening. Emergency preparedness fair. Panguitch, UT. (30 participants)
Jan 2011 Both Drost and Black will be presenting at a winter grower conference in Powell WY.
- 31 March 2010 Early Season Frost Protection for Tomatoes in High Tunnels. Graduate Student Symposium 2010. Utah State University
3 August 2010 Frost Protection for Early High Tunnel Tomatoes. American Society for Horticultural Sciences. Palm Desert, CA
3 August 2010 High Tunnel Strawberry Production Systems for High Elevations. American Society for Horticultural Sciences. Palm Desert, CA
- 3 Mar 2008 “High tunnel production: possible and profitable!” Statewide in-service training for USU Extension Horticulture and Agriculture county agents. Held at the Greenville Research Farm. Logan, UT. (38 participants – all Extension professionals).
24 Mar 2010 “High tunnel resources available through USU Extension” Presentation to the Statewide NRCS Advisory Council, Salt Lake City, UT. (25 participants).
Graduate students Britney Hunter and Daniel Rowley, in an attempt to collect meaningful market data, have been marketing and selling early strawberries, raspberries and tomatoes through the USU teaching greenhouse Plant Shop and at the Logan Farmers Market Consumer interest is quite high with a story appearing in the local newspaper. http://hjnews.townnews.com/articles/2009/07/01/news/news02-07-01-09.txt. Retail sales have provided useful information on pricing points that have been used for the economic analysis and development of enterprise budgets.
Detailed economic analyses have been completed for the strawberry and raspberry systems investigated here. These are included in the Rowley thesis listed below, and will be published by the Utah Department of Agriculture and Food as part of their annual collection of enterprise budgets. Pre-publication drafts have been included in the appendix. Briefly, the spring strawberry production system in a tunnel area of 14’ × 90’ would increase profits by $1,658 relative to field production of equivalent area. The field production was only marginally profitable due to lost yields from spring frost damage to blossoms.
Detailed economic analyses for the tomato and lettuce systems are currently underway and will also be published with UDAF enterprise budgets when complete. These analyses will also be included in the thesis of Britney Hunter listed below.
Estimating the degree to which workshop participants adopt high tunnels and continue to use them has been difficult to assess. Some of our early activities focused exclusively on cropping options and how to properly manage tunnels for optimum growth. However, participants seemed intimidated by the actual tunnel construction. Therefore, a day-long workshop was developed where participants learned the cropping options and management strategies (see previous list), but also worked under the supervision of Extension personnel in constructing a tunnel from start to finish. This proved very successful. After nearly every one of these workshops, participants contacted us for clarification or additional information on construction techniques or material sources, indicating a high rate of initial adoption. After one recent workshop conducted in Duchesne County, the county Extension agent that co-organized the workshop reported that at least 8 commercial-sized tunnels were under construction in his county by workshop participants.
Areas needing additional study
Our research and our dealing with cooperators have further reinforced the need to know and focus on the critical temperatures for plant growth, including: critical temperatures for cold and heat injury, and the base and optimum temperatures for growth. Published critical temperatures for some crops have been useful in developing general grower recommendations (see the bulletin Temperature Management in High Tunnels). However, more information is needed in this area.
Winter protection of both annual and perennial crops remains a limitation. Some cool season vegetables (winter lettuce, spinach, other salad greens) have shown surprising resilience to diurnal freezing and thawing cycles. A better understanding of how some of these crops withstand such extreme cycles while others don’t, would provide very useful information on crop selection and optimization of tunnel conditions, including efficient targeted heat additions.
In many areas of the U.S., raspberries have been a very successful enterprise in high tunnels. This has not proven to be the case in the Intermountain West region of the U.S. Continued winter injury to summer-bearing raspberries and blackberries has been particularly problematic. Winter cane damage, believed to be due to large temperature fluctuations, continues to limit productivity, and approaches to solve this are required. In four-season tunnels such as those used for this research, fall-bearing cultivars tend to fruit too early to capture lucrative late-season markets. Work is needed to evaluate later summer bearing cultivars. Future research should also focus on tunnel management strategies such as using 2-season tunnels to prevent late winter temperature fluctuations from exacerbating winter cane injury in summer bearing types, and for slowing spring primocane development to ensure better late-season cropping potential in fall bearers.