Take a solar greenhouse tour in Asheville this spring
"Sustainability first inspired me to go into the agricultural field more than 15 years ago," Riley said. "But greenhouses aren't always energy efficient. If not designed carefully, they can use a lot of energy.”
In Asheville's Oakley community, Riley grows plants for clients of her native and edible landscape design and garden coaching services. Customers can also order vegetable, herb and flower starts through the MR Gardens website prior to the start of the season or attend plant sales on Saturdays at the greenhouse in spring and fall.
This spring, MR Gardens is offering tours of the nursery’s passive solar greenhouse, designed for the production of plants using nearly all renewable resources.
The 40-minute tours are at 11 a.m. Saturdays from April 8-June 10. The information given on solar design and seedling propagation is helpful for all experience levels — novices as well as avid growers.
It is rare to find a passive solar greenhouse as large as MR Gardens' 800-square-foot house, especially one used solely for a plant nursery. While growers have experimented with similar structures since at least the 1960s, most of them are backyard hobby greenhouses for producing food in the ground year-round. A few small vegetable farmers incorporate passive solar techniques in their greenhouse designs, but not many commercial growers in the nursery trade.
For optimal solar gain, the south-facing roof slants at a 55-degree angle so that the bottom edge nearly reaches the ground, ending at a 3-foot knee wall. On the north, west and east sides of the building, thickly insulated walls prevent heat from escaping.
The specific angles of the building determine how much sun enters the building at various times of the year. When deciding the specifications of the design, Riley considered the time of year she’d be using the greenhouse the most and what type of vegetation she’d be growing.
In the spring, the greenhouse remains within a temperature range of 55 to 85 degrees, ideal for the summer transplants Riley is growing at that time. In the winter, it rarely drops lower than 50 degrees, suitable for the native perennials, herbs and spring vegetable starts in the greenhouse then.
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 sun enters the house. Vents along the sides, front knee wall and roof peak ensure adequate air circulation.
The water barrels not only emit heat during cool nights but also regulate the temperature on hot days. "It's like living next to a body of water, where the temperature fluctuations are less extreme," Riley said.
The winter just passed offered ample opportunity to put the design to the test. On unseasonably warm 60-70-degree days, the greenhouse remained below 90 degrees as long as all the vents were opened at sun-up. The greenhouse also stayed sufficiently warm during short, cloudy, cold days of early January.
The 5 inches of snow on Jan. 7 was proceeded by several overcast days with little sun to warm the barrels. Yet even when it dropped to 20 degrees outside, the minimum temperature inside at night was 45 degrees. These results were repeated the following night when the outside thermometer dropped below 10 degrees.
While sustainability is the primary goal of the project, Riley has found that the greenhouse has other benefits. "It's an ideal environment for seedlings,” said Riley, who has been growing seedlings for sale since 2011. “The plants grow faster and are an even higher quality than past years.” She explains several theories why it’s such a good growing space during the greenhouse tours.
To attend a greenhouse tour, RSVP to megan@mrgardens.net or 828-333-4151. Tours are offered at a sliding scale with a minimum of $5 per person. To learn more about the nursery, visit mrgardens.net.
