Winter Greenhouse

View the project final report

• 2009 annual report

Commodities

• Vegetables: broccoli, carrots

Practices

• Production Systems: general crop production

I have a PhD in physics from the University of California, San Diego; and have worked for about 22 years as a professional physicist, mostly in high energy physics, but early on in the remote sensing of agriculture. I am now retired and own a 75 acre farm located in White, SD. The winter greenhouse that will be used as the base of this project was designed and constructed entirely by me. I am now in the third year of its use. Other than the winter greenhouse, I have about 60 layers of organic eggs, all of which are provided to the Southwest Minnesota Poultry Coop. Additionally, I have a small herd of meat goats. The farm provides all of the hay for the goats. I intend this next spring to begin production of organic chicken feed. I have been working in the Brookings area with a number of organization dedicated to sustainable farming practices, including Dakota Rural Action, especially, the Beginning Farmers Program and the Small Farms Group, Buy Fresh/Buy Local Campaign, and with a number of others who are interested in establishing a food coop in Brookings, with an emphasis on local foods. I live in the rural Brookings, SD area. Many of us in the area through such organizations as Dakota Rural Action and the Buy Fresh/Buy Local campaign are interested in increasing the use of locally consumed foods. During the spring and summer months, the availability of local foods might be expected to be abundant, given enough producers. However, during the winter months, lasting at least between November through April, the availability of local produce is seriously challenged. Local consumers have become accustomed to being able to purchase fresh vegetables and greens during these winter months. However, all of it must be transported from sources very distant from their consumption. It is the purpose of this project to begin to address the winter green shortage problem for local food production. My first model for a winter greenhouse originated from a design developed and tested by the University of Missouri at the Southwest Center near Mount Vernon, MO. Over 25 years this design has proven to be successful. In the winter of 2006, when I first moved to White, SD with my family, I designed a winter greenhouse based largely on their design, with some important modifications. In particular, with the aid of a solar elevation model I had used for many years, I determined that at the higher latitudes of South Dakota, the slope of the south facing solar window needed to be steeper than the 45 degrees used in Missouri. In other respects my design is similar. I use 55 gallon drums filled with water to serve as heat reservoirs during the day and heat sources at night. All walls are insulated with R-19 insulation, with reflecting insulation on the north facing roof. In 2007, I used this greenhouse to try to raise greens in raised beds. I was moderately successful at doing this, but was dissatisfied at the temperatures that could be maintained during the coldest and cloudiest parts of the winter. In the very early spring 2008, I visited Carol Ford of Milan, Minnesota. In 2006, She had received a SARE grant (FNC06-642) with the aim of developing a class of winter greens that would prosper in her winter greenhouse. Her winter greenhouse differs from mine in one very important respect: mine is wholly passive and uses no electricity, whereas hers relies to an uncertain extent upon the use of heated forced air to heat both the soil and greenhouse. My intention from the onset was to develop a greenhouse that would be wholly passive, would be cheap to produce, and yet be durable. I have learned a good deal in the now three seasons that I have had my greenhouse, especially regarding the appropriate materials to be used for the large solar window. I originally, following both the University of Missouri design and one developed by the University of New Mexico, used 6 mil plastic. However, I found such plastic to be unable to endure South Dakota winds. Similar problems were encountered using single sheet, locally available polycarbonate sheets. Following Carol Ford's experience, I have now installed 8 mil double wall polycarbonate. While this is thinner than that used by Carol, I believe that this will prove to be adequate and durable. The Missouri greenhouse design employed a double layer of polyethylene plastic that were held separated from each other by air flow. I incorporated this design suggestion into my design by tacking a layer of 6 mil polyethylene plastic to the inside rafters supporting the external solar window. In this way an air gap was maintained without the use of electrically powered blowers. I have continued to use this strategy of increasing the R-value of the solar window, whereas Carol Ford's design makes no attempt to augment the R-value. In conversations with Carol Ford, and especially with her husband, Chuck Waibel, who designed their greenhouse, I have seen a possible way of increasing the solar efficiency of my greenhouse without resorting to active heating methods. However, those modifications may prove to be inadequate. Generally, a design or design modification is tested over a significant fraction of a growing season, or perhaps over several growing seasons. It is the purpose of this project to implement those changes, or others presently unforeseen, and to monitor the effect of those changes upon soil temperature. In this way design modifications can be assessed quickly for a given greenhouse design and environmental conditions.

RESEARCH
In particular, I intend to bury around the periphery of my extant greenhouse foam board insulation in an attempt to slow the rate of heat flowing from the greenhouse into the cold surrounding ground. Additionally, I will increase the number of 55 gallon drums filled with water. At present, I have three raised earth planters constructed from cinder blocks that have been painted black. Following Carol Ford's experience, I will additionally experiment with using rain gutters as shallow planters for the winter greens. These I will use either hanging from the ceiling or laying atop water filled drums. I will also experiment with the use of plastic canopies over the growing greens as a means of conserving water during the day and heat at night. These modifications may prove to be inadequate so other modifications are envisioned. For example, Carol Ford's greenhouse forces heated air through a deep bed of rocks beneath the greenhouse floor, which then percolates up through the soil, thereby heating the soil. There may be passive means of doing the same through raised beds, relying upon the rising of hot air within the greenhouse during the day. Additionally, one could imagine placing soil containers in solar heated water baths. A winter greenhouse at the University of Manitoba, using a somewhat different passive solar design, found that by using a thermal blanket covering the solar window at night they could reduce the heat loss through the window by a sixth. They covered the window from the outside. Given South Dakota winds, it might be more prudent to employ some sort of insulating system from the inside. In any case, this represents another strategy that might be employed.

Both the University of Missouri and Carol Ford have come a long way in indicating the kinds of greens that can successfully grow in winter greenhouses located in the northern latitudes. This is especially true of Carol who has experimented widely with more exotic greens, many of an Asian variety. Her success with the more traditional vegetables, like broccoli, lettuce, and spinach, has been limited. Whereas, the University of Missouri has successfully grown spinach, lettuce, broccoli, and carrots, among others. It would be useful from a marketing perspective to be able to compete head-to-head with produce trucked in from distant sources. With this in mind, perhaps horticultural assistance might be provided either through the University of Missouri or through the local South Dakota State University horticulture department in assessing the possibility of successfully growing such popular varieties of vegetables and greens. In discussions with local restaurant owners I find significant interest in purchasing locally grown produce. However, they are primarily interested in these more popular varieties, and very little in the more exotic ones. Perhaps with time a taste for these little known varieties will develop. Indeed, Carol Ford has successfully gathered a dozen or so happy clients. One wonders, however, whether such greens will ever be able to find favor with any significant fraction of the community. It is, after all, the aim of the local foods movement to not merely attract a tiny fraction of the community to its cause. For it is only by garnering a significant fraction of the community's food consumption that locally produced foods will have a significant impact upon the character and economy of the community.

If the goal of significant local consumption of winter greens and vegetables is to be ever realized, considerable groundwork will have to be laid in establishing the design and construction of affordable winter greenhouses. It is not until the research and development has been largely completed can we expect winter greenhouses to be widely used to provide local winter greens and vegetables. As a first step in this process, we need reliable means of testing the effect of various designs and design modifications on relevant conditions within the greenhouse environment. With this in mind, this project will purchase monitoring instruments for recording the temporal values of solar irradiance, ambient outside and inside air temperatures, soil temperatures and water temperatures in the 55 gallon drums. Measurements will be taken with the aim of correlating the various measurements and evaluating the effectiveness of various strategies. Effectiveness will be judged in accordance with the changes in ambient air temperature and soil temperature.

Measurements of winter greenhouse performance have been made elsewhere, in particular at the University of Manitoba and in China, where significant work has been done since the 1980s'. However, the bulk of this research and practice has been as a means of getting an early spring start, usually not operating before February or March, or at latitudes lower than that in South Dakota. For these reasons, it would be desirable to begin establishing local experience for the development of winter greenhouses in the upper Midwest that is concerned not only with bedding plants, but additionally in the growing of greens and vegetables suitable to the area. I would intend, where possible, to make similar measurements of other winter greenhouses, in this way obtaining a more general understanding of the parameter relationships. The only other winter greenhouse in the area, of which I am aware, is owned by Carol Ford. For this, and other reasons, Carol is listed as a participant in the project.

While the bulk of this project will be the development of an affordable winter greenhouse design and corresponding strategies to optimize soil temperatures, attempts will also be made to extend the work of Carol Ford in determining what varieties of greens and vegetables might be successfully grown in a wholly passive solar greenhouse. It is hoped that varieties that are more commonly known in the upper Midwest might be found. It is with this in mind, that I intend to utilize resources available to me at South Dakota State University. I know several members of the horticulture department at SDSU, one of which, Rhoda Barrows, is listed as a participant in the project.

OUTREACH
I intend to share any information derived from this project and any subsequent experience with other farmers through the Beginning Farmers Program currently under development by Dakota Rural Action. This program expects its inaugural classes to begin in the Fall of the 2009. I would also offer a tour of my greenhouse, its use and instruments to the general public probably through DRA, not unlike the one sponsored by the Land Stewardship Project of Minnesota of Carol Ford's greenhouse. Additionally, I would be willing to provide my services in the development and performance measurement of other winter greenhouses in the area. I would also consider publishing my findings in a journal of interest to the sustainable farming community.

EVALUATION
My intention is to develop various strategies that will optimize the growing environment inside a winter greenhouse. These strategies will include some changes to the overall structure of my extant greenhouse, but such changes will necessarily not be extensive at this time. For this reason, I intend to investigate various strategies that might be economically employed for a given winter greenhouse. I will evaluate these strategies based upon a few simple criteria:

1) The cost/benefit analysis of the strategy, with the emphasis being on economical and easily implemented strategies.
2) The soil and ambient air temperatures resulting from the modification, with the emphasis being on optimizing soil temperatures. Since dumping heat is of little concern during South Dakota winters, it is higher average temperatures, a perhaps just as importantly, higher low temperatures, that is of primary concern.
3) The yields and rate of growth of some varieties of vegetables and greens will be evaluated. These results will be simultaneously obtained with the parameter measurements. But because over the duration of the grant the growing season is short, these results will be largely preliminary.

The major impact of this project will likely not occur during the period of the grant. I hope that out of this investigation will accrue not only benefits in my own development of a winter greenhouse, and the construction of a larger greenhouse for a more actively commercial venture, but that it will serve to motivate others to take advantage of this work and that of others in the development of a vibrant arm of the local production of fresh food for local consumption.