The magic of a Deep Winter Greenhouse

Andrew and Margo Hanson-Pierre with their Deep Winter Greenhouse. Submitted photo
Andrew and Margo Hanson-Pierre with their Deep Winter Greenhouse. Submitted photo

Farmers across the region are finding ways to extend the growing season in order to provide locally grown foods for more of the year. 

High tunnels are a common way of doing this. A high tunnel is like a greenhouse, but unheated, and you plant into the ground instead of growing in pots on tables. The heat from the sun warms the air and soil during the day, but temperatures inside can dip to near-outside temperatures at night. 

Andrew and Margo Hanson-Pierre from Clover Bee Farm in Schafer, Minnesota, are trying to get more control over these temperature swings by building a Deep Winter Greenhouse (DWG), also called a passive solar greenhouse. 

These work by creating a heat sink, something that will store the heat from the sun during the day and release that heat at night so growing temperatures can remain more stable. 

The floor of Clover Bee’s DWG is made of 4-foot-deep river rock, but people also use large barrels of water as mass for a heat sink. The rock (or water) stores the heat from the day’s sun using circulation fans set up with a thermostat. At night, the fans move the warm air up from the rock, and during the day, they move cool air.

While harnessing the sun is not a new technology, there aren’t many DWGs in Minnesota. In 2009 two farmers in Milan, Minnesota, published “The Northlands Winter Greenhouse Manual,” complete with plans, growing schedules and pest and disease management techniques. Since then, the U of M Extension has published plans and resources for DWGs. The Hanson-Pierres used these plans to build their DWG. 

They’ve opted to build the DWG as a lean-to on the south side of their barn. This allows them to utilize the existing structure and put to use space on their farm that couldn’t be used for anything else. Three sides of the DWG are made of plywood and are heavily insulated, and the south-facing wall is made of polycarbonate sheeting and sits at a 60-degree angle, in order to maximize sunlight.

The Hanson-Pierres also have a high tunnel, which they use primarily for tomatoes in the summer to protect from “late blight,” a fungal disease that spreads quickly through spores in the soil and can take out a tomato crop in a matter of days. They also have a caterpillar tunnel (a lower, less permanent high-tunnel-like structure), which they use to get heat-loving crops, like peppers and eggplant, into the ground earlier than they could without that extra protection.

After farming for six years, they started investigating Deep Winter Greenhouses because they wanted to learn “a whole new set of skills.” 

 “[We’re] trying to think about how to make our business more sustainable for our lifestyle as we get older,” Margo Hanson-Pierre said. 

They’re looking for ways to spread out the labor over the course of the year, and the plan is for the DWG to provide winter income through an off-season CSA, allowing them to decrease their summer vegetable production and maybe go camping someday, or enjoy summer. 

“With climate change, it’s more important to have [produce] when people in Minnesota can’t get it,” Hanson-Pierre said.

Deep Winter Greenhouses are expensive structures to build. So far, the DWG has cost the Hanson-Pierres $16,000, and they still need to purchase insulation and pay back a $7,000 crowd-sourced loan. Because of the cost of the structure, it is imperative that Clover Bee is able to generate enough income from the DWG to pay back their lenders and continue to make the investment worth the 180-plus hours they’ve put into planning and building it.

Their plan is to mostly grow greens through the winter growing seasons. The greens will grow in hanging gutters in potting soil. When each crop is done, the Hanson-Pierres will compost the used potting mix in order to avoid fungal disease. 

They hope to have it up and running by March. Look for their winter greens at next winter’s Neighborhood Roots indoor markets.

Neighborhood Roots indoor winter market

Join us inside for farm products, ready-to-eat foods, music, jams, pickles, crafts and more at Bachman’s on Lyndale.

When: 9 a.m.-1:30 p.m. Saturday, Feb. 8 and March 14

Where: Bachman’s Garden Center, 6010 Lyndale Ave.