Mailbag: Sustainable Greenhouses
JULY 20, 2007 - Critics of local eating have pounced on energy life-cycle comparisons like, say, the energy efficiency of shipping in field tomatoes from far away in the winter versus producing them locally in coal-heated glasshouses. We say: eat seasonally. It's always tomato season in our world, too: green tomatoes in late spring/early summer; red and fresh through to late fall; then dried, canned, or smoked through the cold weather. By eating local foods in season, Alisa and I have no doubt that we radically reduced the energy associated with our diet. But we'd welcome a study...
Meanwhile, one of our blog readers happens to know a lot greenhouses that don't require gas, oil, or coal heat. Here's a note we received from Dottie at Simply Solar Greenhouses in Bell City, Montana:
Composting using shredded leaves, trimmings, etc can bring the temperatures in a greeenhouse up by as much as 125 degrees. In your area [the Pacific Northwest] the solar-heating process of painting barrels black and filling them with water would be the best for heating greenhouses through the night -it gives off the most even heat. Also, a "busy" greenhouse full of plants, pots, etc requires the least heating because there is less air mass to heat. And don't locate your greenhouse under evergreen trees. Summertime trees provide shading but evergreens block out the winter sun. There are lots of ways to warm a greenhouse without fossil fuels.
Dottie's greenhouses have automatic vents for cooling, blocking agents to protect the plants from ultra-violet rays - in short, a bunch of smart-tech features but no fossil-fuel consumption. And yes, she tells us, they're being used near Bell City to grow tomatoes through the winter for a local restaurant.-JBM
