Article last updated February 8, 2022
M R Gardens offers tours of the nursery’s one-of-a-kind passive solar greenhouse, designed for the production of plants using nearly all renewable resources. The information given on solar design and seedling propagation is helpful for all experience levels—novices as well as avid growers.
M R Gardens Owner Megan Riley aspires to grow plants that are as sustainable as possible. Growing seedlings with practically 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 as a graduate student in 2001," Riley said. "But greenhouses aren't always energy efficient. If not designed carefully, they can require a lot of heat and cooling.”
Riley grows plants for clients of her native and edible landscape design and garden coaching services. The general public can also reserve plants online at nativeplantsasheville.com, which opens for pre-ordering prior to the start of the season, or attend plant shows on select days in spring and fall as posted at mrgardens.net.
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| As printed in the Asheville-Citizen Times |
When people think of solar design, they often picture solar panels with photovoltaic cells which convert sunlight to electricity. But a passive solar greenhouse does not necessarily need these panels. The building remains warm because water in barrels store heat collected on sunny days and then emit it when outside temperatures fall.
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 three-foot high kneewall. 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 rays enter 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 the range of 55 to 85, which is ideal for the summer transplants Riley is growing at that time. In the winter, it doesn’t get below 45 degrees, suitable for the native perennials, herbs and spring vegetable starts in the greenhouse then. By opening the vents, she can keep the temperatures at 70 to 75 degrees on a sunny day, which most perennials prefer.
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M R Gardens’ passive solar greenhouse on an early January day. Outside, daytime temperatures were 20 degrees, while inside it was 85. Overnight, the lowest it dropped inside was 45, even when temperatures fell to 10 degrees the following night.
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The structure is 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 sides, front kneewall and roof peak ensure adequate air circulation.
The water barrels not only releases 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.
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Vents along the sides, front kneewall and roof peak ensure adequate air circulation so that it doesn't overheat on unseasonably warm days. |
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| To open the roof vents, Megan stands on a stool and lifts up wood poles that hold the vents in place. |
At the time of construction, Riley's research revealed that heating a conventional greenhouse cost $4 to $5 per square foot in the course of the winter. That equals approximately $4,000 per year for a building of similar square footage. That number does not include the large expense of powering exhaust fans that are typically on the ends of greenhouses. Over time savings in these energy costs make a passive solar design economically feasible.
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 plants for sale since 2011. “They grow faster and are an even higher quality than past years.” She explains several theories why it’s such a good growing space during greenhouse tours.
Go to nativeplantsasheville.com to schedule a tour or contact megan@mrgardens.net or 828.333.4151. Tours are $40 for a maximum of five people, or $10 per person for larger groups.
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| Inside the greenhouse early April 2017 |
