Organic Winter Production Scheduling in Unheated High Tunnels.

Project Overview

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


  • Vegetables: beets, carrots, greens (leafy), radishes (culinary), turnips


  • Crop Production: relay cropping
  • Education and Training: decision support system, demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research, workshop, technical assistance
  • Energy: energy conservation/efficiency
  • Farm Business Management: new enterprise development, budgets/cost and returns, community-supported agriculture, feasibility study, risk management
  • Pest Management: disease vectors, mulching - plastic, row covers (for pests)
  • Production Systems: general crop production
  • Sustainable Communities: local and regional food systems, partnerships


    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).

    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.