A one-of-a-kind passive solar greenhouse aimed at producing plants with all renewable resources is now in the Oakley community of Asheville.
As part of her edible landscaping and garden coaching business, Megan Riley of M R Gardens aspires to grow plants that are as sustainable as possible. Producing seedlings with no supplemental heat or high-powered exhaust ventilation is a big step toward that goal.
“Sustainability first inspired me to go into the agricultural field 15 years ago,” Riley said. “But greenhouses aren’t necessarily sustainable. It can take a good amount of resources to produce plants. For years I dreamed of designing a passive solar greenhouse, so when I finally acquired enough land for a nice-sized building, I didn’t hold back, even though the technology is still experimental.”
It is rare to find a passive solar greenhouse as large as M R Gardens’ 800-square-foot house, especially one used solely for a plant nursery. While similar structures have been experimented with since at least the 1960s, most of them are backyard hobby greenhouses for producing food in the ground year-round. Some small vegetable farms incorporate passive solar techniques in their greenhouse designs, but the technology is virtually unheard of in the nursery trade.
With windows facing south for optimal solar gain, the greenhouse collects enough heat throughout the day, which is then stored in drums of water and emitted at night. Insulated walls with a high R-value prevent the heat from escaping the building. Therefore, no supplemental heat is needed to keep the greenhouse within the ideal growing range of 55 to 85, even during 20-degree nights.
The structure is also designed so that it doesn’t overheat on late spring and summer days. As days lengthen and the sun is high in the sky, it moves above the slant of the roof, and less direct rays enter the house. Vents along the side, roof and front kneewall ensure adequate air circulation. “In a typical greenhouse, it can feel unpleasant to stay very long on an 80-degree day, as temperatures can easily reach above 100,” Riley said. “But we seek refuge in the comfort of a passive solar greenhouse on a hot day.”
The water barrels help regulate the temperature. Before Riley installed them, the greenhouse climbed out of her preferred range. Since incorporating them, unseasonably hot days don’t stress out the plants—or the grower. “It’s like living next to a body of water, where the temperature fluctuations are less extreme,” Riley said.
The project, which included the purchase of more than two acres of land, is financed through Natural Capital Investment Fund, a business loan fund that provides debt financing to small and emerging businesses. They focus on entrepreneurs and enterprises that are good stewards of natural resources.
“I am so grateful to have played a role in helping Megan bring her dream to life, one that has such positive impact for the larger community,” said Erika McGilley, Western North Carolina Regional Lender. “This is entrepreneurial conservation at its best!”
While sustainability is the primary goal, Riley was surprised to find that the greenhouse has other benefits.
“It’s an ideal environment for seedlings, so the plants grow faster than what I’m used to and are higher quality than ever,” she said. Her only challenge has been marketing the plants quickly, before they become too large for containers.
Tomato seedlings, which typically take six to eight weeks to grow out to a size big enough to plant, only took four to five weeks. The warm, sunny spring certainly contributed to the fast growth. Nevertheless, Riley hypothesizes that the large amount of light entering the tall south-facing acrylic windows, which then bounces off the white walls and onto the plants, was the primary bolster. The roots of the plants also likely benefit from the heat radiating from the water, since the barrels double as tables.
When M R Gardens customers walk into the greenhouse, they are stunned by the beauty of the plants. “I am so humbled and pleased when long-time growers tell me how perfect everything looks,” Riley said.
Riley offers tours of the passive solar greenhouse on Saturdays at 11:00 a.m. through June 18. RSVP by contacting [email protected] or 828.333.4151. See www.mrgardens.net for more information.
M R Gardens’ plants can be found at Oakley Farmer’s Market on most Thursdays in May and June, at the French Broad Food Co-Op, at LOTUS Farm and Garden, and at on-farm Saturday sales at 441 Onteora Blvd.