Final Report for OW10-325

Project Type: Professional + Producer
Funds awarded in 2010: $38,358.00
Projected End Date: 12/31/2010
Region: Western
State: Colorado
Principal Investigator:
Frank Stonaker
Colorado State University
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Project Information


Crop production scheduling for winter growing in unheated high tunnels of hardy organic vegetable crops was undertaken by five collaborating farmers and at Colorado State University between October 2010 and March 2011. The participating farms represent a diversity of climatic regions around Colorado, ranging in altitudes of 5,000 to over 6,200 feet above sea level. Lettuce, spinach, mache, carrot and radish were sown in randomized plots in plastic-covered high tunnels on a monthly schedule for five months beginning in October. Data collection included temperature (inside and out of tunnels), days to emergence, yield and product quality. Production methods were standardized for all locations by providing the participants with instructions, seed from common lots, planters, irrigation supplies and data loggers. One of the participants failed to complete the project due to a heavy snow that collapsed her high tunnel.

It was generally concluded that all of these crops will survive Colorado winters in unheated high tunnels when a single layer of floating row cover is applied over hoops, and that late fall and late winter seeding dates were the most productive and potentially the most profitable of the five planting dates. Extremely cold temperatures (-10 to -20 F) in January killed crops sown in December. The slow maturation of the carrot plantings, which have the longest season of all of the crops grown, illustrated the value of early crop establishment for winter productivity and careful selection of appropriate species and cultivars. All of the crops sown in December and January were so delayed that mid-winter planting provided little advantage over late winter sowing dates. Temperature data collected from all of the sites varied considerably, however the range of temperatures between the ambient and the protected environment was consistent, offering nearly 20 F protection in cold weather.

Production scale trials will be necessary to provide accurate economic analysis of winter high tunnel production.


Season extension with the aid of high tunnels is quickly being adopted by specialty crop market farmers across the United States. Summer production can be extended several weeks in frost prone areas; increasing income and on-farm employment potential. Winter production of hardy crops is also being tested to enable farmers to further utilize the potential of their high tunnels. This project addressed questions pertaining to the scheduling of hardy crops in unheated high tunnels through the fall and winter, with the objective of establishing optimal timing for greatest production of marketable products during the winter and early spring season.

In order to collect a good set of data reflective of the many different production areas and microclimates in Colorado, as well as capturing the collective knowledge of practiced high tunnel growers in the state, five market farmers representing three distinct regions agreed to collaborate on this project. They provided not only insight into production techniques and marketing interests, but also unique sets of data that reflect a much greater body of information than can be captured at a single site in a single season. The farmers involved are Daphne Yanakakis and Don Lareau (Zephyros Farm, Paonia), Clara Coleman (Divide Creek Farm, Silt), Anne Cure (Cure Organics, Boulder), Melissa Betrone ( Cortez), and Nic Koontz and Katie Slota (Native Hill Farm, Fort Collins.) A sixth site was the CSU Horticulture Field Research Center (Fort Collins). Each of these sites represents areas with the highest density of market farms in the state and provides a cross section of climates found in Colorado – ranging from the high desert of southwestern Colorado to the mesas flanking the Colorado River, the fruit producing valleys of western Colorado and the piedmont of the Rockies in northern Colorado’s Front Range.

Winter production in high tunnels in Colorado presents both challenges and opportunities; high diurnal swings of temperatures, high winds and occasionally heavy snow loads are countered by high light conditions and low relative humidity. The crops chosen for this project had been grown in high tunnels at CSU in a pilot project in 2009 that evaluated their winter hardiness when fall planted; all crops selected had survived near 0 F temperatures inside the tunnels. The crops and varieties grown in the current project were: spinach (Tyee cv.), lettuce (Winter Density cv.), mache (Vit cv.), radish (Crunchy Royal cv.) and carrot (Napoli cv). In this project, monthly seeding of each crop, from October to February was evaluated.

Comparisons of performance allowed us to evaluate each seeding date and each crop. Data collected included: days to harvest, yield and marketable quality.

Soil and air temperature data (outside of tunnels, inside tunnels and under floating row cover inside the tunnels) was collected in order to compare the sites and identify production limiting temperature ranges during the six-month period.

Project Objectives:

The objective of this study was to expand the understanding of how to best utilize high tunnels for organic winter vegetable production throughout Colorado. Specifically, we aimed to identify successful production scheduling of sequential plantings to ensure a continuous harvest and develop a better understanding of the time requirement of different crops to reach harvestable size throughout the winter months.

To achieve these objectives, we conducted repeated experiments at six different farm operations from October 2010 through March 2011. Additionally, temperature data was collected at each farm both within and outside of the high tunnels to observe the degree of protection that high tunnels provide and crop response to these conditions. Using the combined data, the best timing of successional plantings of five distinct vegetable crops (mache, carrots, lettuce, radish and spinach) was estimated in order to achieve marketable harvests throughout the winter.

Information dissemination was planned and provided to audiences of growers, potential growers and extension agents. This included two on-farm short courses, a major Colorado farm conference (presentations available on internet) and an interview about the project that is posted on the internet (see Appendix C).


Click linked name(s) to expand
  • Melissa Betrone
  • Clara Coleman
  • Anne Cure
  • Dan Goldhamer
  • Nic Koontz
  • Daphne Yannakakis


Materials and methods:

The farmers selected for this project are well established market farmers with several years of experience as high tunnel growers. The farms were located in areas of Colorado where there is a relatively high concentration of market farmers and high tunnel growers, including the eastern front range, the Gunnison River Valley and the southwestern corner of the state (Figure 1). Individual tunnels varied somewhat in design but are reflective of what is commonly used in the industry.

Soil samples from the high tunnels were collected and analyzed (Ward Labs, Kearny, Nebraska), and amendments were made using composted dairy manure at application rates to achieve similar fertility levels among all the sites before the trials were initiated.

The collaborating farmers received specific instructions for their high tunnel planting design (Appendix 1, Figures 2 and 3). Additionally, co-PI Dan Goldhamer, visited each of the sites to review the design details and assist the farmers with initial set up.

Five hardy vegetable crops were sown on a monthly schedule for five months using a Johnnys six row seeder (Johnnys Selected Seeds, Winslow, Maine) (Fig 4.). The crop and cultivars used were: lettuce (Winter Density), spinach (Tyee), mache (Vit), radish (Crunchy Royal) and carrot (Napoli) (Johnnys Selected Seeds, Winslow, Maine). The plots were 3 feet wide and the width of the six-row seeder was 1.25 feet. The plots were irrigated using Dramstix (Dramm Corp, Manitowoc, Wisconsin) misting heads and covered withAgribon 19 (Polymer group, Charlotte, North Carolina) floating row cover draped over wire hoops. Soil and air temperatures were monitored outside of the high tunnel, inside of the high tunnel and under the floating row cover with shielded Sensitech Temptale4 data loggers (Sensitech, Beverly, Massachusetts) (Figure 5).

Harvest parameters were discussed with the collaborators and the uniform standards listed below were agreed upon. When the crops achieved these standards, they were harvested. Salads were weighed, and individual carrot and radishes were counted. Yields were converted to pounds or roots per square foot of growing area.

• Carrots roots would be harvestable when the root cross section was equivalent to a dime’s diameter.
• Radish would be harvested when root cross section was equivalent to a quarter’s diameter.
• The salad crops were to be grown to “baby greens” size:

o Lettuce: 5-6 inches (average length of longest leaves)
o Mache: rosette diameter of 4-5 inches on average
o Spinach leaf (petiole excluded): 4-5 inches (average length of longest leaves).

Research results and discussion:

As expected, crop emergence and days to harvest were delayed significantly for all crops during December and January. Mid-winter plantings were also more susceptible to freezing than crops that had been well established before extremely cold temperatures arrived (Appendix D.).

• Mache, a very hardy salad green, was exceedingly slow to establish at all sites, and no measureable yield was obtained.
• Carrots that were sown in October were not harvestable until March. November through February plantings failed to reach harvestable size before the end of this study in early April.
• Radish was the quickest crop to reach harvestable size, with the October planting averaging 63 days to harvest across all sites. Time to harvest nearly doubled when sown in November. Radish produced harvestable roots from December through March, but November and December sowings were killed in some locations during an extremely cold period in early January (-20 F ambient, +13 F under floating row cover in tunnels).

o October radish sowings produced reliable harvests from all locations between November and mid-December, with one location harvesting in mid-January.
o November sowings were frozen-out in all but two locations; these were harvested in mid-February and early April;
o December sowings were frozen-out in all locations but one that was harvested in March.
o January sowing produced good harvests by late March and early April in all but one location.
o February sowings produced a harvestable crop at three of the locations from early to mid-April; two other locations terminated the project before radishes reached a harvestable size.

• Lettuce emerged and reached harvestable sizes in all but one sowing in which the lettuce was killed during a cold snap in January when temperatures under the floating row cover reached 13 F. Lettuce was harvestable in December, March and April, with late plantings catching up with early plantings. Emergence was rapid for all planting dates.

o October lettuce sowings were harvested from mid-December (four locations) through mid-January (one location).
o November sowings were harvested from mid-February through the end of March.
o December sowings were frozen-out at three locations and harvested in mid-March and early April in the other locations.
o January sowings were harvested from three sites from mid-March through early April and frozen-out at two sites.
o February sowings produced crops from early April well into May at three locations and failed to mature in time at two locations.

• Spinach reached harvestable sizes in all sowings, but some plantings were frozen-out. Spinach was harvested from December through April with late plantings catching up with early plantings. Emergence was slower than lettuce, but consistent stands were produced for all planting dates.

o October spinach sowings produced harvestable crops from mid-December through mid-January at all locations.
o November sowings were harvested from four sites between mid-February and mid-March and froze-out at one site.

o December sowings were harvested from two sites between early and late March. Three sites lost this planting to freezes.
o January sowings were harvested in mid-March to early April from three locations. Two locations froze-out.
o February sowings were harvested from three locations between early April and mid-May while two locations terminated the trial before harvest.

As illustrated in Figure 6, a mid-January and-mid-February harvest gap resulted from slow crop establishment and freezes in January. It is expected that better established crops, i.e., earlier plantings, may mitigate hard freeze damage and reduce or prevent this mid-winter harvest gap. Additionally, minimal heating could be used to maintain higher temperatures, thus protecting the more sensitive crops.

The lack of data presented for carrot and mache plantings was due to their slow establishment during short-day periods. This underscores the value of early establishment of these hardy but slow growing crops.

Heavy snows and winds in mid-December collapsed one of the collaborator’s high tunnels in Cortez, CO and no data was collected. Snow and wind loads on lightweight high tunnel structures are very real risks that need to either be mitigated by additional bracing and structural strength for winter production or vigilance to reduce the accumulation of snow loads. Of course, avoidance of these risks is not always possible (Figure 13).

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Outreach efforts for this project have included two on-farm short courses and a conference presentation at the Colorado Agriculture; Big and Small Conference in Adams County (February 2011). More than 80 attendees were present at the on-farm short courses, hosted by collaborating farmers Clara Coleman (Divide Creek Farm, Silt, CO) and Anne Cure (Cure Organic Farm, Boulder CO). Power point presentations were given at the short-courses which included visits to the high tunnel sites, followed by question and answer sessions. A survey was taken of the attendees to determine their knowledge of winter production methods (before and after the short-course) and the degree of benefit/impact the materials had on attendees (Appendix B).

Additionally, knowledge and experience derived from this project has been included in high tunnel production presentations to farmers and extension personnel attending the webinar presentation “High tunnel specialty crop production in Colorado” given by D. Goldhamer (April 4, 2011) and “Season extension for high altitude gardening” presented by F. Stonaker at the High Altitude Gardening workshop (CSU Extension, NRCS, Nederland, Colorado, April 16, 2011), and “Five years of high tunnel research at CSU” presented at the Colorado Big and Small Conference (Adams County, Colorado, February 2, 2011). An interview by Bruce Burkhart for Assignment Earth about this project is posted on the internet (Appendix C). The presentations are available on CSU extension web sites and the CSU Specialty Crops Program web site (see Appendix C). Preparation for publication of CSU Fact Sheets on winter vegetable production in high tunnels is underway.

Project Outcomes

Project outcomes:

It is too early to determine the impact of the results of this project on farmers in Colorado. However, the positive survey results and well attended field days and presentations indicate high tunnel growers are likely to adopt some of the production methods demonstrated in this project. Survey results from the attendees of the winter high tunnel production workshops were favorable: 78% of respondents were “more interested” or “much more interested” in winter vegetable production in high tunnels than before the workshop (see Appendix B).

The National Resource Conservation Service (NRCS) high tunnel price support program was initiated in 2011 in Colorado and has generated a good bit of interest, it is expected that new growers, as well as established growers, will be interested in extending their production season into the winter months when as it has been demonstrated to be feasible.

Economic Analysis

Economic analysis extrapolated from small plot trials should be considered with caution when using for production scale planning. This study had a high degree of yield variability from site to site and from planting date to planting date (sees Figures 7-12).

Estimates of probable gross returns for winter high tunnel production using results from this study are possible, but further study on a production scale is needed to more accurately establish enterprise budgets and probable profit/loss. Reliable production of spinach, lettuce and radish throughout the winter months and a range of yields obtained from five locations using the same production methods provides a starting point for determining the feasibility of winter high tunnel production.The design of this study was intended to determine the timing of plantings rather than to definitively establish yield potential.

In Figures 7, 8 and 9, yields per square foot of production area are presented. Most high tunnels devote 75%-80% of the floor space to production, so it is reasonable to estimate that spinach and lettuce would produce 1.5 to 2 lbs/ft2 during winter production time slots. Likewise it is estimated that radish would produce approximately 3.5 lbs/ft2. Carrot and mache failed to produce meaningful harvests so no estimates are offered here.

Market price is highly variable in the direct market scenario but is generally closer to retail pricing. In the case of baby lettuce and spinach, direct marketing may bring 3-4 times the wholesale market price. Break-even prices would require a good understanding of production scale input/operating costs, which this study does not address.

Farmer Adoption

The farmers that were involved in this project will continue to produce winter crops to supply their CSAs, local restaurant and wholesale markets. Refining the planting dates to avoid a mid-winter lapse will be required, and the use of limited supplemental heating is planned at three of participants’ farms in the future.

Don Lareau, a project collaborator, stated, “I have learned about how cold crops can go. This winter has been the coldest we have ever seen on our farm and certainly while we have been growing. There has been some quality loss due to the cold (tip burn, etc.) but overall, crops being alive (under these cold conditions) has been remarkable.”

With regard to market opportunities afforded growers using high tunnels, Lareau added: “The markets available to us revolve around the ski towns, so they are endless between Thanksgiving and the end of March. Earlier sales and later sales are possible but are lower. It seems even if we had a whole high tunnel planted to one crop it would be possible to sell it all. These sales are wholesale to middle men or restaurants, and having a steady supply of certain crops is important.”


Areas needing additional study

Figure 6 shows that the planting schedule used in this trial resulted in a mid-winter production gap, when emerging crops were killed by sub-zero weather; those that survived grew very slowly. Earlier planting and establishment of crops may be one solution worth evaluating. Another probable solution is the provision of minimal, supplemental heating during extreme cold snaps. Continued evaluation of cultivars of these crops that may be more tolerant of freezing temperatures will surely provide growers with valuable information. Finally, studies that are conducted at production-scale and are designed to fully evaluate the costs and returns of this production method are needed.

Appendices. Appendix A. Project layout instructions for growers

• The general design is two beds with a sprinkler running down the walkway between the beds. The beds will be 3 feet wide and 47.5 feet long. The two beds will be divided into fifths; one fifth for each planning date. Within each of those planting dates there will be five crops and these will be replicated three times. That means that for each planting date there will be 15 total plots.
• Each plot will be 3 feet wide and 1.25 feet long. Since the seeder is 1.25 feet wide you will be able to seed each plot with one pass.
• Since the plot will be spaced over the entire spray pattern of the sprinkler and the entire plot will be harvested for data, any variability in spray pattern will be averaged through the entire plot.
• The location of each planting date will be randomized as well as the location of the crops within each planting date.
• The irrigation system supplied for the project uses Dramm Stix with Pin Perfect nozzles. These will allow you to easily turn off sections that have not yet been planted. Also, by having all the planting dates in line with another, you can reduce edge effects from the sides of the high tunnel.

Discussions were held to determine the best harvest protocol so that all farmers would be using the same methods and quantitative and qualitative measurements.

Appendix B. Short course survey results

Appendix C. Web site links for materials presenting “Organic Winter Vegetable Scheduling in Unheated High Tunnels”
  • •
    • Interview: “Sustainable Winter Agriculture”, Jay Canode, producer. Assignment Earth.
Appendix D. Temperature data for 5 high tunnels around Colorado 10/11 -4/11


Sincere thanks are extended to the following individuals and organizations for their support of this project.

Western SARE, Johnnys Selected Seeds, Sensitech, Jay Canode and Brad Burkhart, Don Lareau and Daphne Yannakakis, Clara Coleman, Melissa Betrone, Anne and Paul Cure, Nic Koontz and Katie Slota, Jennifer Cook, and Ryan Friedman.

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.