Green roofs take root

Garden centers are a natural place to find green roof technology at work, according to Dr. Robert Berghage, of the Center for Green Roof Research at Penn State University, State College, Pa. Not only because garden center owners have an innate knowledge of plants, but also because there’s already product on hand.

This new “green” frontier shouldn’t be too much of a challenge for garden centers. Horticulture businesses are presumably good at growing plants, understand their needs and have a good grasp of which growing media works best in containers.

“A typical green roof is really just a big, shallow outdoor container with a rock garden in it,” Berghage said. “That being said, the green roof is unique in a number of ways that may pose interesting challenges.”

First, the media is different. “We use an inorganic, aggregate-based media in a green roof rather than the organic potting soil most nursery growers are used to,” Berghage said. “This is because the roof will be in place for many years and an organic potting soil will decompose over that period.”

Then there’s the weight issue. Keeping weight low on the roof is necessary, and can be challenging. Finally, you have to deal with waterproofing and root resistance.

“But many garden centers that deal with ponds already understand this,” Berghage said.

Matterhorn Nursery of Spring Valley, N.Y., is a leader in garden center sustainability. Green roofs are key components of Matterhorn’s focus on energy efficiency and (an) ecologically sound business practice.”

Building it Green
Since the spring, Matterhorn Nursery’s owner, Matt Horn, has been adding green roofs to the covered walkways in the garden center. He has also been selling value-added products with green roofs, including playhouses and doghouses.

“Electricity and water are expensive, and as we have come to learn, they are also finite resources. Ecologically sound practice is our goal,” Horn said. “One of my favorite elements of the new design is the increased use of green roofs. I planned covered green roof walkways, which will join the existing green buildings. Green buildings are beautiful to look at and are good for the environment.”

Horn decided to build green roofs in the garden center because “it was the right thing to do.” But he also stated that it was part of the bigger plan of morphing Matterhorn’s brand into a lifestyle.

“Matterhorn, itself, has become a way of life,” according to Horn, and he believes that way of life includes practicing what he preaches by making his buildings ecologically sound along with the products that he sells.

“Green roofs are so good for the environment,” he said. “They help conserve water and reduce storm-water runoff. Green roofs also become habitats for butterflies, birds and insects. Finally, green roofs are aesthetically pleasing. I can do the right thing and enhance Matterhorn’s aesthetics at the same time.”

Construction Concerns
Horn didn’t just climb on his building’s roof and start planting. Instead, the process took planning and working with other experts before anything too root.

Horn said he used two vendors for projects: The first, LifeRoof, offers a pre-vegetated, modular system. The second vendor is Moerings, which offers Sempergreen products.

Horn said starting the first green roof was simple. He worked with his design team, as well as with a horticulturist and a carpenter. They first built a sunken roof, added soil and filled the roof with individual plants. He added LifeRoof’s pre-vegetated modules, and because he found them easy to use, he and his team decided to renovate another building, using LifeRoof. Also, he worked with a timber company to create doghouses that are covered in LiveRoof material.

Horn did encounter some difficulties along the way:

“The biggest challenge has been the angle of the roofs and making sure the roofs are sturdy enough to accommodate the soil and plant material,” he said. “Early on, there were definitely a few mistakes. We had to work on the edging to make sure it was strong enough to hold the roof in while preserving the look of the roof. The last few projects have been fronted with cedar to make sure the edges are aesthetically pleasing.”

Education was the biggest challenge when it came to selling value-added products with green roofs. “Maybe ‘incentive’ is a better word,” Horn said. “Customers cannot choose a green roof unless they learn about the products and the benefits. Knowledgeable staff members are the key.” Horn advises other garden center owners to teach customers the benefits of green roof products.

“You can’t put a green roof on one little shed and expect your sales to flourish,” he said. “You need to demonstrate the possibilities, and you need to make sure your staff is knowledgeable. People are not going to buy into the green roof [product lines] unless they’re educated and understand the values and benefits. That is where you and your staff come in.”

Plant Selections
Green roofs can be built on most structures, such as pergolas, sheds, playhouses, doghouses, and the like. Berghage said that many of the same plants that work on larger roof structures work well on smaller roofs—sedums, sempervivums, alliums, small bulbs, short, low growing grasses, such as blue fescue, dianthus, small, low-growing alpine species; and other plants. The only constraints are media depth and USDA hardiness zones.

“If you put enough media up there, you can grow anything. I’ve seen people growing herbs and vegetables on garden-shed roofs,” says Berghage.

There’s a process in designing and growing green roofs on any building. Specialty contractors, like landscape designers, horticulturists, carpenters and others may need to be involved in the green roof construction process. Berghage explained that the type of structure and building code requirements will determine how many people need to be on the design team.

“Occupied buildings have code requirements and require more complicated design and design analysis compared to a garden shed or a doghouse,” Berghage said. “In any event, the builder needs to design for the added dead load—30 pounds or so for a 3.5- to 4-inch-thick roof.

“There are many roof tray-systems that can be grown and simply placed on a roof with sufficient loading capacity—for many small projects, these are probably the best choice. For larger roofs, a laid-in-place system may be a less expensive alternative,” Berghage said.

A garden center can handle the “green” section of the green roof construction, but retailers may need to hire a roofing contractor to handle the waterproofing portion of construction, Berghage said.

“Most of the materials used are readily available in the landscape trade. For example, a pond liner makes great waterproofing for a garden shed,” he said. “This is covered by a drainage sheet, such as an enka drain or a j-drain. Then, the media, if weight is not an issue, a blend of three-eighths gravel, sand, and compost will work. If weight is an issue, then lightweight aggregates can be used. The plants are relatively easy to grow and relatively easy to propagate. Or the garden center owner can purchase plants from a number of vendors.”

Green Roof Benefits
“There’s certainly a novelty and a wow factor associated with a green roof,” Berghage said. “There are not many out there, so when you see one, you really notice it. Of course, for a doghouse, you can claim many of the benefits of a green roof on a commercial or residential structure. When it comes to reducing the summertime temperature, for example, a green roof doghouse will be much cooler for Fido than a regular roof doghouse. The roof will also last longer. I know that with my rolled roof sheds, we have had to start to replace or repair the roofs after eight to 10 years. My green-roof sheds have no leaks after 10 years and have required no repair or replacement.”

Horn recognizes green roofs’ eye appeal too. “Well, they look amazing,” he said. “Aesthetically, I just can’t think of another design element that comes close.” Horn also said that when it comes to selling products with green roofs, he can educate, as well as market his products: “It really is a feel-good experience. I love talking to customers about the value and benefits. They tend to get really into the whole green roof, environmentally-friendly idea, and that enthusiasm is rewarding.”

There are at least two drawbacks to green roofs: Berghage said the higher cost and weight for delivery are detrimental to garden centers’ value-added products with green roofs. Horn added that if he could change one thing about his current green roof project, it would be the edging. “I would change the edging on the initial roof. Like I said earlier, we had to learn along the way. I understand a great deal more about angles, weight and edging than I did in the beginning,” he said.

Indeed, garden centers and nurseries are the perfect arenas for green roofs to be used as part of their building designs. Also, if garden center owners have vendors who build value-added products, adding green roofs, can be a unique selling point for their customers.

A member of the North American Agricultural Journalists association, Wendy Komancheck writes about agriculture, family, and the green industry from her home near Ephrata, Pa. You can contact her at wendykomancheck@gmail.com.