By Kathryn Atkins
Minnesota faces unique environmental challenges when it comes to crop production, with its harsh winters and changing seasons. Yet in a 2018 study, Minnesota was ranked the sixth most environmentally friendly state in the country based on three criteria: overall environmental quality, eco-friendly behaviors and climate-change contributions. The University of Minnesota is a driving force in leadership and innovation in this area, largely due to grant-funded research by MnDRIVE initiatives.
One area of research showing great promise is a passive-solar greenhouse model that holds potential to enable small-scale farmers to grow fresh greens year-round in an environmentally sustainable way. A Deep Winter Greenhouse, or DWG, is designed to limit the amount of fossil fuel it takes to grow crops during Minnesota winters.
These greenhouses are unique in their eco-friendly construction, deliberately built in an east-west position, with a south-facing glazing wall that is specially angled to collect the most possible solar energy on the coldest day of the year. The sun heats the air inside the greenhouse, which is blown underground with a fan and stored in rocks. The heated rock bed is a thermal mass which acts as a heat battery and stores heat for when it is needed at night.
A variety of lettuces, herbs, brassicas, Asian greens and sprouts are crops well-suited for DWG production. The innovation holds exciting potential for additional revenue in the agricultural industry, while making fresh local greens more readily available in rural communities.
Five prototype DWGs are now operating or in construction across the state, thanks to support by MnDRIVE, other University of Minnesota programs and a variety of agriculture lending banks. The University of Minnesota Extension’s Regional Sustainable Development Partnerships (RSDP) program worked with a community partner in each region of Greater Minnesota to build a prototype DWG based on a design by researcher Dan Handeen of the College of Design Center for Sustainable Building Research. In exchange for construction support, community partners agreed to be host sites for University research and outreach to test and share the technology with other farmers and gardeners.
Kathryn Draeger, Statewide Director of the RSDP and adjunct professor of Agronomy and Plant Genetics, leads this research. “The support from MnDRIVE Global Food Ventures and MnDRIVE Robotics, Sensors, and Advancement Manufacturing have been very important to this research and outreach effort,” Draeger said.
Support from MnDRIVE Global Food Ventures enabled RSDP to work with John Erwin, Department of Horticultural Science, to look at the production volume and nutrient value of greens grown in DWGs. Later, MnDRIVE support enabled RSDP to work with the Sustainable Farming Association of Minnesota to hold public open houses at the prototype DWGs, sharing the technology with hundreds across the state. Most recently, combined funding from MnDRIVE Global Food Ventures and MnDRIVE Robotics, Sensors, and Advanced Manufacturing supported the installation of thermal mass sensors in three of the five DWG prototypes. A College of Science and Engineering student installed the sensors, and the University of Minnesota Solar Energy Laboratory will use them to study how much energy is being saved in the rock bed and whether there are improvements that can be made.
Not only do DWGs hold promise to protect the environment while supporting farmers’ bottom line, they also benefit consumers. “This is an absolutely premium food product we’re creating,” said Carol Ford, a pioneering DWG farmer who works with RSDP. “We are used to getting week-old greens in a cellophane bag … and that’s nothing like what’s coming from these greenhouses.”
To learn more about DWGs, upcoming events, and to access construction documents, visit RSDP’s DWG resource page at z.umn.edu/deepwintergreenhouse.