Leading garden designers and horticulturists have discovered that sedges fulfill a number of key roles in the landscape and fix problems other plants struggle to solve. They work in dry shade or wet soil, they resist deer browsing, they don’t need spraying, and they sustain wildlife and control erosion. You can even grow them in that most inhospitable of sites, amid the surface roots of old trees. But there is an even greater role for this humble genus: as a replacement for the oceans of mulch that have come to define so many gardens across the land.
“You have to keep applying mulch. With sedge, you plant it once and it’s good to go,” said George Coombs, a research horticulturist at Mount Cuba Center in Hockessin, Del. He is preparing to put some 80 species and varieties of sedges through a methodical three-year trial to determine their value to home gardeners. Another aspect of the trial is to identify varieties that can be used as a substitute for lawns that struggle in the shade. You probably wouldn’t want to walk all over a sedge lawn, but you’d need to cut it only once a year.
Whether sedges will free us of our mulch (or lawn) fixation remains to be seen, but what is clear is that sedges deserve a place in every garden. They have great utility but also bring a contemporary natural beauty to the landscape.
It is their role as a filler, a subordinate plant amid showier blooms and specimens, that gives sedges their power. They are the glue that binds a whole scene together.
Sedges inhabit, mostly, shadier gardens. If you want to use them in full sun, you have to pick your variety with care and make sure it gets enough water. In hot, dry sites, ornamental grasses will be happier while giving a similar effect.
There are two aspects to sedge planting I find alluring. First, they offer ground cover options in areas of dry shade, which is one of the toughest site conditions you can address. Second, they are an alternative to the ubiquitous plantings of old-fashioned or overused ground covers such as liriope, vinca, pachysandra and English ivy. You might add mondo grass to the list, though I still think its diminutive scale is valuable in small gardens.
Sedges are in leaf from late winter to late fall, and some stay green through the winter. This unchanging aspect makes them a great foil to dainty flowering bulbs and perennials that can grow through the field of green leaves.
Many sedges have flower and seed heads, but they are generally not of great ornament. One large species, tussock sedge, has interesting large spiky seed heads in early summer.
Others produce their seed heads in the spring, but sedges are in essence valued for their foliage effects. You can distinguish a sedge from a grass by cutting a stalk — in section it is triangular, giving rise to the adage “Sedges have edges.”
But there is another significant difference that places sedges squarely in a modern approach to ecologically driven gardening. Many of them provide sustenance to the caterpillars of butterflies and other pollinators. The Pennsylvania sedge, for example, feeds as many as three dozen species of caterpillars.
Traditionally, gardeners used Asian and New Zealand sedges as small ornamental plants; the shift in the past five to 10 years has been toward native species that are generally less decorative but when used in blocks and masses provide some of the finest textures of any garden plants. Replacing pachysandra with Pennsylvania sedge, for example, is like exchanging dumplings for angel hair pasta.
“It speaks to a woodland setting that is very soothing and peaceful,” said Shannon Currey, marketing director of Hoffman Nursery, a wholesale grower of grasses and sedges in Rougemont, N.C.
The nursery lists 35 sedge varieties, up from just two in 1991. Most of them are native species or their cultivated varieties. Today’s orders might contain thousands of plants for use in institutional settings or environmental restorations, but many are going to sophisticated, ecologically minded residential gardens, typically designed by professionals.
Sales of sedges have tripled in the past decade, Currey said.
The rise of the sedges mirrors the mainstream acceptance of ornamental grasses a generation ago, and just as some of the early grasses turned out to be inferior garden plants or invasive and fell from favor, the sedges are going through a similar period of introduction and experimentation.
Some seem destined to last. Among the native species, by far the most popular is Pennsylvania sedge, which is apple green, finely textured and forms spreading colonies in the shade garden.
Because sedges are found in a variety of habitats, the gardener is bound to find one that will be happy in a given site, except, perhaps, hot, dry beds with poor soil.
For those areas that are in shade with many competing tree roots and constantly dry soil, the choices include Appalachian sedge, bristle-leaf sedge, blue sedge and Texas sedge.
In difficult wet areas, the options include the palm sedge, Gray’s sedge, Cherokee sedge, Bowles’s golden sedge and tussock sedge.
Some of the showier sedges can be used as accent plants, even in containers, but as ground covers and living mulches, they should be planted in numbers. This becomes more economical if you plant in small sizes and allow them to spread and grow together. They fill in after two or three years.
Sedges grow here
Most types of sedges do fine in southern Idaho climate, says Anju Lucas, head of the perennials department at Edwards Greenhouse.
▪ They need more water than grasses, so are often used around ponds.
▪ They grow best in soil that can retain water, so sandy soil would not work, for example.
▪ They prefer partial shade but should be OK in full sun provided they get even more water.
▪ They are evergreen and will survive typical Idaho winters.