Let It Shine: Solar Heat for Gardening

Reader Contribution by John Perlin
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MOTHER EARTH NEWS featured Chapter 5 of Let It Shine: The 6000-Year Story of Solar Energy (“Winter Gardening throughout the Ages”) on its web site in early January of this year, which I will summarize today as part of the series of summations of the chapters of Let It Shine.

The use of solar heat for gardening began in ancient Rome. Once the Romans discovered making clear glass, they began to use it to trap solar heat inside cold frames and greenhouses to grow vegetables out of season or exotics from hotter climates in Rome’s temperate clime. With the decline of the Roman Empire, the use of transparent glass all but disappeared. Glass was not used again to trap solar heat until the wealthy citizens living in northern Europe during the Age of Discovery, like their affluent Roman predecessors, wanted to enjoy oranges and other fruits from exotic areas such as the newly explored and settled regions of Asia and the Americas or, specific to northern Europe, grow vineyards as did their southern European neighbors. They faced their greenhouses south to optimize solar heat collection.

Solar heat trapping for gardening became even more popular with the advent of the Little Ice Age which made it even more urgent in northern Europe to trap solar heat to allow for the successful growing of non-native plants under abnormally cold conditions. In winter, canvas curtains, rolled up above the south-facing windows were pulled down at night to insulate the greenhouse. Solar heat for horticulture was so valued that the best minds of the period studied the best sun angles and the optimum materials to capture as much sun heat as possible during winter and then attached plants to these sloping walls. Sometimes a greenhouse was attached to the south-side of home’s living room or library, transforming the “dull interior” into a “vibrant” and warm space where people would congregate. On sunny winter days the doors separating the greenhouse from the home were opened to allow sun-warmed air to circulate freely into the formerly chilly interior.

Scandinavians led the movement of green roofs to keep the interiors warm during their prolonged winters. They became the rage in London where city folk could find peace and quiet in the florid world above the hustle-and-bustle of the metropolis.