UP ON THE ROOF
The media has given a lot of publicity over the past few years to “green” structures, including roofs and walls. Green roofs, when properly supported, planted and tended, can keep buildings cooler than conventional roofing materials. Green walls are a way to beautify interior or exterior space by growing plants in pockets, grids or openings in specially designed wall structures. The green wall phenomenon is a natural extension of a normal garden occurrence. Every gardener with a stone wall, especially of the dry laid variety, has found plants growing out of the crevices. Taking this a step further, the English mid-twentieth century doyenne, Margery Fish, deliberately planted small specimens throughout her rock walls.
Green roofs, now fashionable in cities, used to be the exclusive domain of poor and rural people. With wood in short supply, settlers in the American Midwest used materials close at hand to build themselves sod or sod-roofed houses. The English and many other groups have created thatched roofs for centuries.
I am fascinated by the plants that have traditionally grown on “green” roofs. Botanically many of them are distinguished by the species name “tectorum,” which is Latin for “roof.” Now, when the need for tough, adaptable plants is greatest, these traditional tectorum plants have experienced a resurgence in popularity.
Probably the best known roof plant is Sempervivum tectorum, a succulent sometimes known as the houseleek. It boasts wonderful common names including Jove’s beard, Jupiter’s eye; Thor’s beard; St. George’s beard, old man and woman, live-forever, hens and chicks and—my favorite—welcome-home-husband-though-never-so-drunk. Sempervivums are low growers, forming rosettes of grey-green succulent leaves. Their offspring, the “chicks” of the common name, grow up around them and can be easily detached and transplanted.
Living on a roof can be hot, dry business and sempervivums are well suited for the task. They are surprisingly cold tolerant and even bear lovely flowers. In addition to their practical virtues, houseleeks are reputed to be able to ward off lightening strikes and/or evil—depending on which culture you belong to and which legend you believe. The common names associated with lightening gods like Jove, Jupiter and Thor underscore this association.
If you don’t have the time or energy to grow houseleek on your roof, the plants work well in living wreathes or potted arrangements as well.
Another well known roof plant is Iris tectorum, a native of China often called Chinese or Japanese roof iris. Traditionally these plants were grown on thatched roofs and I can image how beautiful clumps of them would be springing up on top of a house. The long leaves are light to medium green and textured. The plants grow only twelve to eighteen inches tall, with flowers that are somewhat “nested” in the leaves. Usually the blooms are blue-purple, but they can be white as well.
Though Iris tectorum does not have house leek’s array of evocative nicknames, it does have an interesting story. According to the Pacific Bulb Society’s website, at sometime in the past, the Japanese emperor decreed that only food plants be grown on arable land. The dried, ground roots of Iris tectorum were traditionally used to make face powder, which women were loathe to give up, so the plants were lifted from harm’s way and moved to the thatched rooftops.
The species name “tectorum” also turns up affixed to a couple of grasses. One is a noxious agricultural pest called Bromus tectorum or cheatgrass. The species originated in Eurasia and most likely arrived in the United States in shipments of grain. Though it is somewhat useful as a forage plant, it is invasive and outcompetes most other vegetation in places like the intermountain West, where it has taken hold. Another roof plant is the South African native, Cape Rush or Chondropetalum tectorum, which is sometimes sold, especially in California, as an ornamental grass. Though information is limited on the reason for assigning the high altitude name to the two grasses, I assume that at some point in time both were used as thatching materials in their native areas.
The roof of my Victorian house is not conducive to the “green roof” treatment and I have a feeling that the plaster interior walls wouldn’t take kindly to the idea of supporting a “green wall.” My Sempervivum tectorum are planted in a raised bed in the back garden. I am tempted to install some Iris tectorum nearby, just to keep them company.
Succulents have become so popular that sempervivums are available just about everywhere these days. If you have a yen to decorate your roof or other areas with Iris tectorum, you can purchase one from Plant Delights Nursery, Inc,.
9241 Sauls Road, Raleigh, NC 27603, (919) 772-4794; www.plantdelights.com. The print catalog is available for the unconventional price of 10 first class stamps or one box of chocolates.