Comparison of Coverings Over Permanent Raised Beds to Extend the Growing Season for Year Round Food Production

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2008: $6,000.00
Projected End Date: 12/31/2010
Grant Recipient: Prairie Birthday Farm
Region: North Central
State: Missouri
Project Coordinator:
Dr. Linda Hezel
Prairie Birthday Farm LLC

Annual Reports


  • Vegetables: beans, beets, onions


  • Crop Production: continuous cropping, no-till
  • Education and Training: demonstration, on-farm/ranch research
  • Energy: solar energy
  • Farm Business Management: budgets/cost and returns
  • Production Systems: organic agriculture
  • Sustainable Communities: local and regional food systems


    Prairie Birthday Farm (PBF) is a 15-acre, biodiverse, sustainable farm and land stewardship effort, which strives to mimic nature in design and diversity of species. It includes heirloom and wild fruit and nut trees and bushes; tall grass prairie (as habitat for beneficial insects, amphibians, and birds), honeybees; permanent raised-bed heirloom vegetable gardens; a culinary herb and edible flower garden; as well as bramble/vine gardens. Pastured chickens and ducks as well as two horses on rotation-paddock pastures provide for on-farm compost production. Produce is sold to area residents from the Farm and to chefs at area restaurants.

    A total of seventeen raised beds (4 x 16 feet) are dispersed around the farm to take advantage of variable growing conditions and micro-climates, deter insect infestations, minimize rampant disease events, and mimic natural diversity as much as possible.

    Since beginning farming on this acreage in 1995 the following sustainable practices have been implemented: Over the past eleven years they have become more sophisticated and complex but always used at some level.
    • on Farm compost production
    • crop rotation
    • biodiverse crops
    • integrated pest management
    • soil testing and amending
    • cover crops
    • rotational grazing
    • pastured poultry
    • prairie reconstruction
    • prairie burns
    • invasive species removal
    • no-till
    • permanent raised beds
    • mulching
    • biodiverse bird habitat and food sources
    • heirloom and regionally adapted and/or native plants
    • no synthetic chemicals
    • permaculture principles
    • botanical foliar sprays made from herbs and plants on the farm
    • insect habitat plantings


    Goals: This project identified 3 different removable covers and evaluated the food production results of various combinations of them when placed over permanent raised beds. The growth of four crops were observed to determine which covers and their combinations might enable successful winter production of these crops in this Zone 5 location.


    A permanent raised bed (prb) is a growing space filled with compost that is constructed with rigid walls and stays in place permanently or for many seasons, in comparison with a raised bed being plowed down and reconstructed every year as with more conventional practices. For this project, the prb is constructed of 8x8x16; 40-pound concrete block stacked two tall. Each 64-block bed is 4 feet x 16 feet. The prbs are oriented east to west in an area approximately 50 x 100 feet.


    Steps involved:
    Raised Bed Construction/Cover — Eight, previously constructed permanent raised beds, filled with compost made on the Farm, were outfitted for winter growing by:
    • Installing in the holes of the concrete blocks, approximately every four feet, along the long axis (east/west orientation) of the beds, two vertical pipes embedded in concrete.
    • Flexible pipe (two courses to hold covers above the soil) will be inserted into the vertical pipes in the concrete on each long axis and arched north to south over the bed.
    • Thus, each bed will have one course of five arched pipes, approximately 3’ at the highest point of the arch.
    • A second course of five shorter arched pipes approximately 2.5’ at the highest point of the arch will be below each of the above pipes.
    • Remaining holes in the concrete blocks will be filled with compost to provide insulation and for solar heat storage. These become added growing space from April through October when the beds are uncovered.
    The beds were outfitted with multiple combinations of row covers to examine which combinations are needed to trap and store solar heat to protect cold tolerant crops from killing frost. These materials (clear polyethylene, 3 and 6 ml thick and floating row cover) were chosen because they are readily available, useable by one person, easily stored when not in use, and reusable over several years. Exterior covers were held in place with wood posts placed on top of the edge of the cover on the ground along the long axis of the bed. Beds were randomly assigned to the treatment covers.
    The eight prbs were covered (treated) as follows:
    • No covers to serve as a control (Bed G).
    • One course of six ml polyethylene on the upper most arched pipe (Bed H).
    • Two courses of six ml polyethylene suspended on 2 courses of arched pipes over the bed and thus separated by an air space (Bed B) .
    • One course of three ml polyethylene suspended on the upper most arched pipes (Bed A).
    • Two courses of three ml polyethylene suspended on arched pipes over the bed and thus separated by an air space . (Bed C)
    • One course of six ml polyethylene suspended on the upper most arched pipes over the bed plus a layer of floating row cover (14 mil, 2 oz. per square yard), (Bed D).
    • One course of three ml polyethylene suspended on the upper most arched pipes over the bed plus a layer of floating row cover placed directly on the growing space over the plants (Bed E).
    • One course of six ml polyethylene on the upper most arched pipe and one course of three ml polyethylene suspended on lower arched pipes over the bed and thus separated by an air space (Bed F).



    Temperature Control/Monitoring — The south walls of all beds were wrapped in black plastic (removable in summer) to use the concrete block wall as a passive solar collector. Placed in the center, inside each bed were two temperature probes. Soil probes were placed at 4 inch depth, and air temperature was measured six inches above the soil. Air temperature probes were shielded to avoid false readings due to solar gain. All probes were attached to a micro data collection station to measure, record, and graph on a personal home computer using a data shuttle, the internal minimum and maximum soil and air temperatures relative to the ambient air. Crop planting, growing and harvest logs were matched to the various cover combinations and temperature measurements to identify optimal conditions in which to grow winter hardy crops in covered permanent raised beds. Beds were not opened to make visual observations during extreme cold (below 30 degrees F) and deep snow, but observations were made as ambient air temperatures permitted. Manual ventilation (opening and/or uncovering) was provided to beds when external air temperatures were above 40 degrees.



    Test Crops — Four crops (fava bean, Swiss chard, beets, perennial onion) were planted in each bed to determine their responses to the various growing conditions. These crops were chosen for cold hardiness, nutritional value, length of production, and salability. All were seeded directly into the beds as fall plantings. All crops were planted in all areas (sides, ends, and center) of the beds to ensure comparable growing conditions.
    Irrigation — Given that rain could not permeate the various treatment covers, a bucket-drip irrigation system was installed in fall and spring so that beds received adequate water without exposing them to ambient air during cold, but above-freezing temperatures. Bucket drip irrigation was chosen for the following advantages: minimal investment, lasts several years, needed water is applied directly to the soil, can be installed and used by one person, adaptable to small farms and growing spaces, kits and instructions are available retail. During rain events above freezing, covers were taken off to allow rain watering.


    No other farmers, ranchers, or businessmen assisted with the project.

    Fava bean leaves 29 plus pounds in fall 2009, before they froze; 50 plus pounds of greens April to May 2010; onions 100 plus pounds across all months; yields are combined for all beds because of extensive vole damage. Voles pulled entire beet and chard plants underground. Voles had not previously been a problem at this site and therefore were not anticipated. Above average snow fall kept beds buried for extended periods of time and thus provided safe habitat for them.


    Field analysis:
    In beds that survived the voles, enough growth survived to provide the beets and chard an early start in the spring. Onions did splendidly under the covers and are a viable crop for this process.


    Related data:
    Temperature graphs (enclosed) from the beds reveal the temperature variations among treatments. Soil temperatures remained remarkably similar among treatments. Solar temperature gains under covers was significant and surprisingly similar among cover combinations. Failure of the control data logger was a significant disappointment and a major loss of comparison information.

    The micro-climate of the Farm resulted in sustained growth under all cover combinations. Even single plastic layers provide some growth protection. Double plastic layers require closer observation for extreme heat on sunny days with ambient air temperatures above freezing.

    How do these compare with conventional systems used previously?
    Conventional systems for this Farm were uncovered beds. Onions survive in uncovered beds but do not flourish. No other crops survive uncovered beds.

    The results are consistent with the pilot project conducted on the Farm prior to the grant application submission.

    Were these results what you expected?
    It was expected (because of pilot project) that some crops would grow differently under various treatments. Greater variation among treatments did not occur as expected.

    The extensive vole damage was new to this site and therefore not anticipated.


    What would you do differently next time?
    • I will set passive vole traps (commercially available as: Tin Cat) in the fall with the cover installation.
    • I will also not drape the covers as far out on the ground surrounding the bed. I will wrap the covers higher and tighter around the beds to provide less vole habit.
    • I will continue to search for and trial new winter hardy crops to determine the most likely to succeed
    • I will use a minimum and maximum thermometer to get daily feedback on the conditions inside the bed.
    • I will try different plants every season.
    • I will begin trialing different means of access during winter months.
    • I will put fewer species in each bed and concentrate on those most notable for winter hardiness.


    • Food growing in covered raised beds is possible in this Zone 5.
    • Crop selection is crucial. Much more experimentation with various crops will be ongoing.
    • Micro-analysis of weather conditions with expensive, complicated equipment is not transferable to other growers. A less technical instrument, like the minimum and maximum thermometers used in my pilot project is more generalizable to other situations and more accessible to more growers.
    • Covered raised beds are a valuable season extension tool in fall and also allow earlier sowing and transplanting in the spring.

    How has this affected your farm or ranch operation?
    • I am more intentional, informed and consequently productive. I produce more food during more months of the year.

    What are the advantages and disadvantages of implementing a project such as yours?
    The multiple advantages of raised bed growing systems were substantiated:
    • Retain the roots of previous crops for improved organic matter.
    • Protect soil organic matter/biota from the degradation of weather conditions
    • Amend soil between and for individual crops
    • Improved drainage and early access during wet springs
    • Promote earlier growth as soil warms earlier
    • Use high-density plantings (shade to soil, decreases evaporation, impedes weed germination, and keeps roots cooler)
    • Better protect plants from high-wind events with the prb low profile
    • Provide water only to the beds/crops and not to the pathways
    • Protect plants with pest-deterring covers (bird netting, floating row covers)
    • Create forages for micro-livestock (poultry, rabbits)
    • Accommodate physically challenged growers who require elevated work surfaces
    • Install prbs in many growing spaces without a building permit
    • Use agroforestry principles to grow shade-dependent food plants by alley cropping with prbs between trees.

    The disadvantage is primarily the lack of access to the food during snow and extreme cold. Design of a system or process which facilitates greater access across the growing season is the next goal.

    If asked for more information or a recommendation concerning what you examined in this project, what would you tell other farmers or ranchers?
    • I would enthusiastically endorse covered, raised beds for year round food growing.
    • I would attempt a verbal assessment of their site and operation. Following my basic understanding of those parameters, I would customize the process for their specific needs. Each grower and site will have specialized considerations. I would encourage their experimentation on their site.


    A simple survey (copy included) was conducted at the outreach events to learn the likelihood that attendees could incorporate the information into an agriculture venture and what potential barriers to implementation attendees identify. Most prominent barrier to implementation was perceived cost, though no cost per bed was stated. Many had no experience with raised beds. Many stated they would incorporate at least some of the information that was presented into their growing practices.


    1. On Farm educational tours.
    Number of tours: 4
    Number of attendees: 70
    Type of attendees: growers and eaters
    2. One-on-one educational demonstrations to Farm apprentices (5).
    3. Formal presentations.
    • Annual Farmers Forum at National Small Farm Trade Show and Conference in Columbia, MO (approximately 110 attendees).
    • Extension program on writing for a SARE grant (approximately 30 attendees).
    4. Individual communications (email and phone).

    What plans do you have for further communicating your results?
    • Will be posted to the Farm web site.
    • Webinar (09-19-11), MO. Beginning Farmers Program, University of MO. Extension

    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.