The purpose of the project was to determine the feasibility of using solar and wind power to extend the growing season in high tunnels using vertical growing systems. Strawberries were planted in vertical columns with a water pipe through the center of the column which was attached to a water tank. Supplement heat was provided by two 1 kw windmills through 12 volt hot water heater elements. The heated water was pumped through the vertical columns in the late fall and early winter. The plants were also covered with a heavy row cover and the high tunnel was constructed with two layers of plastic kept apart with a blower that was powered with solar panels. The entire system utilizes no fossil fuel or purchased electricity.
While no difference in temperature was noted between the heated and unheated water columns, the effect on the whole greenhouse was season extension. Fruit was produced in the high tunnels from April through December in 2011. Having fresh, high quality local fruit production was a big advantage for our markets.
A total of 546 pounds of salable fruit was harvested from the 20’ X 48’ section of the high tunnel which is a production of .5 pounds per square foot or a value of $2.00 per square foot.
Horizontal rows of strawberries were also successful and may be the better choice as they are easier to construct.
Over the last four years, Ryan’s Glade Farm has grown around 2000 everbearing strawberry plants in raised beds. Yields have been (depending on treatments like film color –black, silver-white or flower removal treatment) very good, typically 1.5 lbs per plant. Fruit size is consistently over 12 grams. Heavy rains reduced the percent marketable fruit, and forced the use of a fungicide. This has made it clear that we must use tunnels in our region for day neutral varieties like Seascape, Everest and EV2.
All of our farm’s produce including peppers, tomatoes, squash, cucumbers, cabbage, broccoli, etc is marketed at the Oakland Farmer’s Market. Strawberries are a major source of income and we would like to expand to plantings in tunnels which would improve quality and expand the growing season. I have limited amount of space to add high tunnels therefore I have purchased a heavy duty high tunnel that would allow me to use a vertical growing system instead of using lighter weight tunnels and growing in the soil. We receive over $4 per pound for our fruit. Thus, the economics of a more advanced production system is warranted.
Willie Lantz, University of Maryland, Ag and Natural Resource Extension Educator served as the Technical Advisor for the project. Willie assisted with the construction of the project and provided guidance. Willie also provided assistance with outreach activities. Dr Harry Swartz, retired University of Maryland horticulture professor and plant breeder provided design assistance with the project. Dr. Swartz has been breeding strawberries all over the world and has experience with growers that grow strawberries in vertical systems. The system used on the farm was adapted from a system in the United Kingdom. Justin Hunt, University of Maryland, Horticulture Program Assistant also assisted with construction of the project.
To extend the growing season in tunnels, we proposed to use wind and photovoltaic solar technology in a vertical growing system to heat the soil for strawberry production. Water was run through the center of the vertical columns to provide enough heat to extend the growing season. We looked at how long we could extend the growing season and the production of strawberry plants in this system.
We built a 20 x 72 foot tunnel with double polyethylene sheets inflated with a solar powered fan. On one end of the tunnel, we built a 958 gallon = 8 ft x 4 ft. x 4 ft deep insulated concrete form storage tank with an R-value of 40+. Over one day, this tank was expected to lose about 230 BTU per degree F difference with the outside and ground temperatures. We inserted four 12 V 600 Watt “Power dump” heater elements with the capacity to add 8188 BTU per hour to the water, enough to increase the temperature of 1000 gallons 0.6?F (per hour). The heaters are powered by two 1-kWh wind generators (turbines).
To deliver this heated water we used a submersible fountain pump. The output of the pump is attached to two one inch polyethylene tubes which be run through the center of the vertical growing columns. For this work, the vertical columns were placed 3 ft in the row and 5 feet between rows (9 per row x 4 rows). The return pipe will be run from the top of the next column back to the main on the ground. Each upright tube consists of 5 to 6 “links” arranged as a string of sausages. The rows of vertical columns were also designed so that each could be covered with a heavy (3ounce) row cover during cold weather. This also reduces the heating losses around vertical columns.
The vertical grow systems were planted with the following strawberry varieties:
Seascape, Albion, EV2, Sweet Eve, Strawberry Festival and San Andres. In addition 47 potted Marcianna fall bearing raspberries plants were included in a 12’ section of the tunnel in line with the 4 rows of strawberries.
Two of the four rows were “heated” with the water from the tank, while the other two rows were not heated. Temperatures were monitored daily during test days. Data on fruit yield and size were recorded. Plants were initially planted in the summer of 2010 for fall production. Plants produced some yield in the fall of 2010 (about .17 pound per square foot). Plants were over wintered in the system. While the plants survived the winter about one quarter of the plants were replaced with new plants of a more productive variety (San Andreas).
There was no measurable difference between the vertical and control unheated) and treatment(heated) columns so the fruit produced was not separated for measurement between them. It was observed that the system studied did not create enough temperature difference between the water being heated with the windmills and the temperature of the tubes since they are black. Also,the water volume was not that great going through the tubes.
The system worked well to overwinter plants in our harsh winter environment. Water was run through the system until the end of December. After that the plants were covered for the remaining part of the winter. The plants resumed growth and covers were removed in mid March. The plants were renovated by removing dead plant material and about a quarter of the plants were replaced with bare root San Andreas plants. The first fruit was harvested from spring bearing Strawberry Festival on April 28th and from day neutral varieties on May 1st. The strawberries produced fruit for the entire remaining part of the year with the last fruit being harvested on December 31, 2011. Fruit was sold at every tailgate market from early June until the end of October. A total of 546 pounds of salable fruit was harvested from the 20’ X 48’ section of the high tunnel which is a production of .5 pounds per square foot or a value of $2.00 per square foot.
The windmills were utilized starting in November to provide additional heat to the water tank. Water tank temperature in November and December averaged in the mid 40 degrees F. The system provided adequate temperatures for production to continue in very cold outdoor conditions, however the rows of strawberries without the heating tubes also continued to produce fruit. Pulling the covers every evening provided adequate heat retention for the plants.
The raspberries in the high tunnel produced quite well. Each of the containers produced 2 pounds of fruit. Raspberries were harvested from June to December with fruit selling at every farmers market from the beginning of June through the end of October.
Planting the strawberries in 2010 was delayed therefore the yield on these plants in 2010 was low. The late planting produced a total of 166 pounds of marketable fruit. In order to examine what spring planted plants would produce we replanted 1/4 of the plants in the spring of 2011. Overwintered and spring plants produced well in 2011. Some of the initial varieties did not produce well. These varieties were replaced in the spring of 2011. We also experienced problems with our first windmill that was erected in the fall of 2010. The windmill had a plastic hub that broke under high wind conditions in late November. Until a replacement hub could be secured, winter was in full force therefore the hub was not replaced until the fall of 2011.
The greatest benefit of the project was to be able to sell high quality fruit at every farmers market. Having fruit at every market is a great draw for our table. While the initial cost of the system to produce fruit using high tunnels and the vertical system is higher that of outdoor systems, the increase in quality and the ability to sell at a premium ($4.00 per pound for strawberries and $7.00 per pound for raspberries) increase our farm income. The windmills, solar panels, double layer plastic (powered by a solar panel) and crop covers provided adequate temperature protection to provide extended fruiting without the use of any additional fossil fuels. We also like the fact that harvesting the fruit from the vertical system was much easier and labor intensive than harvesting fruit in the field. We enjoyed the fact that we could harvest in any weather conditions and that fruit quality was very consistent throughout the year. These factors will make strawberry production on our farm more sustainable long term.
Education & Outreach Activities and Participation Summary
Several organized and individual tours of the project were given. In September of 2010, a group of local fruit and vegetable producers toured the project as part of a series of high tunnel visits. In the summer of 2010, a group of West Virginia University extension agents and producers visited the project to learn more about season extension beyond traditional high tunnels. A group of local middle school students working on a research project for food safety visited the tunnel to learn more about how local foods can be produced for more months in Garrett County. The project was used as model of how to increase local food production while reducing risk of food borne illnesses.
The project was also part of a field day that was held in the fall of 2011 entitled “Saving Energy: Extreme Season Extension with Greenhouses and High Tunnels”. Information from the project was also used for part of a presentation that was made at the University of Maryland Eastern Shore’s Small Farm Conference – Pre-Conference Workshop on season extension presented by Willie Lantz, Dr. Swartz, and Mike Newell. Information will also be presented by Willie Lantz at the West Virginia Small Farm Conference in March of 2012. Over 200 individuals have or will receive information that was learned from the project.
While constructing the vertical columns we discussed the idea of running the columns horizontally. We did install 36’ of one row horizontally to determine if production would be the same. Our concern was if there would be adequate light for the lowest row which was at ground level. The plants performed well it he horizontal rows. The horizontal rows were much easier to construct and were easier to maintain soil moisture levels at the proper level. We may consider adding more horizontal rows in the future. We also learned that certain varieties such as San Andres, Sea Scape and Albion developed in California did better than varieties developed in the United Kingdom. We are planning to replant a majority of the plants this spring with the San Andreas variety.
We also have learned much about how to use solar power on our farm. We have installed a solar powered water pump to pump water that is collected from the high tunnels and other building roofs back to a 1500 gallon tank at a higher elevation. This provides much of the water that we need for our four high tunnels.