When the days start to gain noticeable light and we begin to bump up toward 32 degrees, my “spring thinking” asks: What vegetable seeds should I start this year to rehabilitate last year’s fallow garden? Should I begin planting seeds in trays along our south-facing loft window? Where do I have adequate space heating to transplant the seedlings after they pop up? This year, how do I prevent spindly seedlings from appearing?
I wonder, is this the spring to construct a greenhouse? If so, is one with passive heating (without electricity) best? Are cold frames better? Or do I want to wait until this fall and then put up a deep winter greenhouse (known in horticulture circles as DWG)? Energy and healthy home environmental factors (such as temperature/heating efficiency, lighting, humidity) are what I focus on when thinking through these horticulture questions.
First, I know that through south-facing windows the sun’s radiation provides two necessary factors for growing things: 1) ultraviolet light, and 2) adequate ambient heat around the potting soil and seedlings.
Since I have grown many leggy or spindly seedlings that couldn’t stand and survive on their own, retired Cornell Professor Thomas Bjórkman’s research examining this malformation has been interesting. One contributing factor he has found is light deficiency, which can be remedied by providing supplemental spectrum lighting.
As a University of Alaska Fairbanks engineering professor who studies heat transfer and models thermal systems, Professor Sun Kim has been conducting greenhouse heat storage and distribution in part by experimenting with attachable box-shaped, passive solar air heater panels, which are designed to collect the sun’s radiation through efficient greenhouse glazing (enhanced with low-wattage fans). These move cold air from the greenhouse into the solar heat collector for heating and return it to the growing area.
Similar panels could lengthen the front end of the growing season, allowing plant starts to be transplanted earlier into a well-heated environment while home growers wait for their garden to thaw. The continuous low-wattage, direct current fans that move cold to warm air can be powered by a deep cycle boat battery or small solar photovoltaic panel; this is particularly nice for off-grid or homestead horticulture.
When updating retired UAF Professor Rich Seifert’s “Solar Design Manual for Alaska,” I wrote a section on solar greenhouses (Appendix A), highlighting designs and methods to capture/use the most reliable source of heat and ultraviolet light. One I hadn’t included, which Ryan Pesch, a farmer and professor of agricultural business management at the University of Minnesota Extension, has been working with, is the deep winter greenhouse.
By using passive heat through glazing and solar thermal arrays on the top of the greenhouse, heat is routed and stored in a thermal mass (floor) below the greenhouse, which itself is attached to the south side of another building, he is able to germinate and grow vegetables in frigid, northern conditions through the year. For those who want to grow produce for themselves or sell produce at the summer farmers markets, this style can allow for community supported agriculture boxes to be put together in the winter. Investing in a DWG may be the way to go for larger-scale entrepreneurship.
Spring is approaching. How will you use heat and light toward harvesting a bumper crop this year?
Art Nash is statewide Energy Specialist at Cooperative Extension Ser-vice, a part of the University of Alaska Fairbanks, working in cooperation with the U.S. Department of Agriculture. For questions or comments, contact him at 907-474-6366 or al-nashjr@alaska.edu.
