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The Salt Lake Tribune
Gardening up on the roof, where it’s peaceful and practical
Succulents are a low-care way to go when planning a green roof
It may seem like a no-brainer but, just for the record, access is everything if you’re planning to install a green roof.
If you envision a low-care, no-care kind of cover crop, fine. Plant your rooftop garden with an assortment of succulents and forget about it. Most of those drought-tolerant, winter-hardy plants can look after themselves.
But if you want the meadow look for your roof, then expect to do some weeding, watering, deadheading and replanting. For that, you will need a way to get there, and that’s not a design feature built into many office buildings or homes.
Of the $950,000 spent to build a demonstration green garden on the roof of the American Society of Landscape Architects’ headquarters building in Washington, $600,000 went for a new interior stairway and landing to provide visitor access, officials said.
“There’s a great deal of difference between a highly viewed garden and a purely functional garden,” said Edmund Snodgrass, co-author of Green Roof Plants: A Resource and Planting Guide (Timber Press, 2006).
“Succulents are the most popular,” said Snodgrass, who also owns and operates Emory Knoll Farms and Green Roof Plants near Street, Md. The business supplies plants for over a million square feet of green roofs in 20 states and the District of Columbia.
“The best quality of the (succulent) plant is that it lives on existing rainfall. If you get into a lot of irrigation or maintenance, it just drives the cost of the roof up,” he said. “Look for plants that can withstand drought, wind and all the things that make surviving on roofs more harsh. That points toward succulents.”
Shop around for plants that are both attractive and practical. Many of the sedums are shallow-rooted and well suited to roof plantings. Certain cactus varieties are rugged enough to make it in a thin, inorganic medium. And they don’t go dormant, either, meaning they provide color all year.
If your plant material is 4 inches deep or more, then consider adding some herbaceous perennials (Phlox, Dianthus, Campanula, Salvia and Potentillas, among others). Kitchen herbs can be a smart addition if you have a half-foot or more of soil depth. Grasses are good, too, although some may need to be mowed and irrigated, and they can become a fire hazard when allowed to dry.
Snodgrass’ basic advice:
– Use plugs, two per square foot. They’ll grow into a vegetative roof in about a year and a half.
– Succulents, or “little canteens,” as he calls them, grow readily from cuttings. “It takes a while, but it’s inexpensive.”
– The more juvenile the plant, the better. “They become more adapted to the roof environment.”