What is a Deep Winter Greenhouse?
A Deep Winter Greenhouse (DWG) is a greenhouse designed to limit the amount of fossil fuel it takes to grow crops during cold winters. DWGs are passive-solar greenhouses that rely on energy from the sun to heat the building instead of more traditional heating sources.
There are a few important aspects of the design that make this possible. DWGs are built in an east-west position, with a glazing wall that faces south. This wall is specially angled, depending on latitude, to get the most possible solar energy on the coldest day of the year. The sun heats the air inside which is blown underground with a fan and stored in rocks. This heated rock bed is a thermal mass that acts as a heat battery and stores heat for when it is needed at night.
DWGs in Minnesota can be used to grow crops that thrive with minimal light, providing year-round production capacity for small-scale farmers and gardeners. Crops well-suited to DWG production include a variety of lettuces, herbs, brassicas, asian greens and sprouts.
The University of Minnesota Extension Regional Sustainable Development Partnerships, as part of a statewide initiative to advance DWG technology, have worked with the College of Design's Center for Sustainable Building Research to develop construction documents for two DWG designs.
The Center for Sustainable Building Research designed the earlier DWG 2.0 following an analysis of the performance of several early DWGs in use across Minnesota. RSDP supported the construction of five DWG 2.0s with the following community partners:
- Organic Consumers Association Finland, MN (ribbon cutting February 18, 2017)
- Bemidji Community Food Shelf (ribbon cutting September 30, 2017)
- Grandpa G's Farm in Pillager(ribbon cutting December 8, 2018)
- Alternative Roots Farm in Madelia (ribbon cutting October 29, 2017)
- Lake City Catholic Worker Farm (ribbon cutting May 5, 2018)
Support for the statewide initiative is provided by Extension, other University of Minnesota programs and a consortium of agriculture lending banks:
- Institute on the Environment
- MnDRIVE Global Food Ventures
- AgriBank Farm Credit Bank
- Compeer Financial
- AgCountry Farm Credit Services
Mattson MacDonald Young provided the structural review and structural plans for the statewide DWG campaign prototype.
This Farm Scale Winter Greenhouse is appropriately scaled to offer small and medium sized farms the opportunity to grow vegetable crops for sale year-round. The greenhouse primarily uses the sun’s heat which is captured and stored in a thermal mass. These plans offer different options for thermal mass storage, foundations to accommodate different budgets, and comfort levels with complexity. Though the greenhouse uses solar heat, it will also require an additional backup heat source.
These documents reflect design changes incorporated as a result of the statewide prototype 2.0 initiative.
This report is helpful for urban and non-profit organizations that are looking to build a DWG. These case studies will explain some of the extra considerations that might be necessary.
For those who are looking to build a DWG on a budget, this report explains some of the techniques used by experienced DWG producers to build your own affordable structure for winter production.
Carol Ford, Chuck Waibel
Supported by RSDP, the Northlands Winter Greenhouse Manual provides detailed and easy-to-read construction specifications for building a DWG in northern climates as well as production techniques for successfully growing crops.
This guidebook highlights the successes and lessons learned by growers across the Midwest who have designed and built cold-climate greenhouses to grow produce during the winter with minimal reliance on fossil fuel-based heat.
ATTRA, National Center for Appropriate Technology
This site contains a large amount of useful information about solar greenhouse design.
This lightening talk demonstrates the basic principles of DWG technology using an 8' by 11' model.
Producers can use these tools to estimate the revenues and expenses they might expect with a DWG enterprise.
This research report examines the ability of DWGs to be viable business models. Results are based on analyses of eight deep winter producers in Minnesota in the winter of 2017-18.
Learn how to grow winter hardy crops in your Deep Winter Greenhouse.
Get advice and tips for building and laying out shelving for planters in a DWG system.
This report provides recommendations for DWG producers using passive solar technology for cold tolerant crops like leafy greens.
Year one research trial results of DWG horticulture trials in DWG prototypes.
This is a list of crops that producers have found to work particularly well in the DWG system.
This poster displays results of analyses of various potting soil mixes for the common DWG crops of mizuna, arugula and giant red mustard.
This poster highlights research results on day/night temperature effects on kale plant growth.
These case studies provide the stories of three different DWG producers. Learn what inspired them to build a DWG, what drives them to produce, and lessons that only those with experience can tell.
This report highlights progress on a variety of research projects underway to look at the potential to maximize winter vegetable production. Results of analyses of day-night temperature effects on plant growth; vitamin C content of different fertilizer mixes; light response curves of kale; and vitamin C depletion rates are included.
This poster was presented at the Midwest Organic and Sustainable Education Services 2015 annual conference. The poster highlights results from trials that examined the performance of different fertilizers used in winter production.
Deep Winter Greenhouse: Heat storage systems and their trade-off's
DWG webinar from 2021, featuring Shannon Mutschelknaus (Wayward Springs Farm) and Dan Handeen (UMN Center for Sustainable Building Research). They share their experiences concerning heat storage and thermal mass applications in passive solar winter greenhouse systems.
Deep Winter Greenhouse Designs: DWG 2.0 and Farm Scale DWG
In this webinar from June 5, 2020, Dan Handeen explains the designs of the older DWG 2.0, the new Farm Scale DWG, and takes questions from the audience.
Growing plants in the deep winter greenhouse
This webinar from June 2, 2020 features Carol Ford and Shayne and Louise Johnson of Grampa G's Farm. Get a video tour of Shayne and Louise's DWG and learn about how farmers use these structures to grow winter vegetables.
Growing plants in deep winter greenhouses
This webinar from May 28, 2020 features Carol Ford and Brooke Knisley of Alternative Roots Farm. Get a video tour of Brooke's DWG and learn about how farmers use these structures to grow winter vegetables.
DWG research convening: November 4, 2016
Current and future DWG producers, RSDP staff, and University faculty, students and researchers discuss past projects and research and future research needs.
Watch the seminar or download the presentation (PDF). The 2016 DWG research convening summary provides an overview of the research convening and a list of project ideas and research topics that participants identified.
DWG history, design and future aspirations
University of Minnesota College of Design researcher Dan Handeen presents to the Minnesota Renewable Energy Society on this history, design and future aspirations of the DWG project (September 2016).
DWG research seminar: November 4, 2015
DWGs: An overview
A quick overview of DWG pioneer and author Carol Ford's DWG that presents the general concept of the technology.
DWG research convening held November 4, 2016
On November 4, 2016 the RSDP hosted a research convening made up of current DWG producers, prospective DWG producers, University staff and faculty, and other stakeholders. This group shared their past research with each other and brainstormed ideas for projects to address current DWG production needs. View the 2-hour-long presentation, download the presentation (PDF), or check out the overview document to see a list of research and project ideas.
Construction begins in statewide DWG campaign
(News release, September 2016)
Construction has begun on the first of five prototype DWGs being built around the state as part of the statewide DWG campaign. In spring 2016, an advisory group selected five partners to build prototype DWGs for research and outreach purposes. In exchange for support for building the prototype DWG, partners agreed to provide access to their DWG for University research projects, public workshops, and demonstrations for a period of three years. Events will be announced here and on social media channels.
The statewide DWG campaign is being conducted by the University of Minnesota Extension Regional Sustainable Development Partnerships (RSDP) along with the Center for Sustainable Building Research (CSBR) at the University of Minnesota College of Design.
Partners include the Bemidji Community Food Shelf, Grandpa G's Farm in Pillager, Organic Consumers Association in Finland, Alternative Roots Farm in Madelia, and Lake City Catholic Worker Farm. Construction has begun on the Organic Consumers Association DWG, with others to follow in 2017. RSDP received more than 40 applications in response to the statewide DWG campaign, and an advisory committee selected one partner from each of RSDP's five regions in Greater Minnesota.
The campaign is made possible by support from the University's Institute on the Environment and a consortium of farm lending banks, including AgCountry Farm Credit Services, AgriBank, AgStar Financial Services, and United FCS. Mattson MacDonald Young provided the structural review and structural plans for the statewide DWG campaign prototype.
Researcher Dan Handeen discusses the design and inspiration for DWGs
Montevideo American-News talks with Researcher Dan Handeen of the College of Design’s Center for Sustainable Building Research about his DWG prototype.
DWG pioneer Carol Ford gives TED talk
Carol Ford shares her personal DWG journey with TEDxMinneapolis.