The fashion in gardening is moving away from the free-form style of the cottage garden to one of more massing — using just a handful of plant species but grouping them in large quantities.
You will find this at the Chicago Botanic Garden’s Evening Island in Glencoe, designed by James van Sweden, which showcases scores of switch grass, goldenrod and other perennials planted in large swaths for a bold, natural look. Some 66,000 perennials of 66 species, along with 13,400 ornamental grasses of 12 species are grouped there in what is often described as the New American Garden.
Like those used on Evening Island, there are many perennials suitable for use as ground covers — ground-hugging plants to shrubs up to three feet tall that have the ability to spread and suppress weeds.
You may be familiar with the common types — ivy, vinca and euonymus — but there are countless others that can help suppress weeds and provide color, especially if you have a spot in the garden that receives six or more hours of direct sun.
“Sun often offers more possibilities than shade,” says landscape architect Charles Fisher of Clarendon Hills. “Low woody shrubs and roses, masses of perennials and grasses, and mat-forming flowering plants make for great ground covers.”
Some of his sun-tolerant favorites that provide multiseason interest include the native grass little bluestem (Andropogon scoparius), `Walker’s Low’ catmint, Hypericum `Hidcote,’ Perovskia `Little Spire,’ `Gro-Low’ sumac, `Nearly Wild’ rose and creeping thyme.
“A ground cover planting may be a small or expansive monoculture, or it may be a tapestried herbaceous border, or a prairie-inspired mixed-species planting,” Fisher says. Being sensitive to your garden’s soil and site and using your imagination, Fisher says, “can lead a gardener to many plants not previously used as ground covers.”
Here are four sun-tolerant ground covers to look for this spring. All are hardy in Chicago’s Zone 5 climate.
Lavandula angustifolia `Nana’
Zones 5 to 10
This dwarf blue lavender grows slowly, forming dense mounds of fragrant foliage with thin blue flower spikes above blue-gray leaves. Lavandula angustifolia “Nana” grows about 10 inches tall and about 16 inches wide.
“Lavenders can be quite tall,” says Ava Salman of High Country Gardens in Santa Fe, N.M. “If you have a smaller setting, this one is nice. It’s only about 10 inches high, so it’s nice for a rock garden or for edging a perennial border. And it’s one of the more cold-hardy lavenders.”
Like sedum, lavender is best used in an area that has extremely well-drained soil. Its heat tolerance makes it useful along walkways. “Lavender requires sharp drainage, so in our soils, it is best to add coarse torpedo sand as an amendment,” says horticulturist Barbara Collins of Elmhurst.
She recommends mulching lavender with a layer of finely crushed limestone. Collins cuts back dead branches in spring to promote growth. After the plant finishes blooming, she cuts it back by one-third to improve the shape.
Combine lavender with coreopsis, blue oat grass, sedum or annuals, such as petunias, zinnias and low-growing cosmos. The foliage mellows to a silvery-gray by winter.
Aster novae-angliae `Purple Dome’
Zones 3 to 8
Beginning in September and lasting nearly a month, a profusion of 1-inch bright purple flowers cover this compact, mildew-resistant New England aster. At 18 inches tall and up to 30 inches wide, `Purple Dome’ produces a mass of color that attracts migrating butterflies.
Full sun and evenly moist soil keep `Purple Dome’ performing at its best. In late June, cut all of the stems back halfway to keep the plant compact and to produce more blooms.
Pair `Purple Dome’ with Sedum `Autumn Joy,’ coneflower, fountain grass (Pennisetum `Little Bunny’), perovskia, liatris, Joe Pye weed, `Fireworks’ goldenrod and butterfly bush.
Festuca glauca
Zones 4 to 8
At 8 to 10 inches tall and wide, this diminutive clump-forming grass offers a delightful dash of color to the summer garden.
“The mounds of blue-green finely textured leaves of this grass are a great contrast in the garden,” says horticulturist Ron Picco of The Morton Arboretum in Lisle.
Heat and drought tolerant, fescue struts its stuff when planted with coreopsis, sedum, gaillardia, penstemon, lavender, veronica, salvia and catmint. All of them prefer full sun and a well-drained soil.
Depending on the cultivar, fescue’s fine leaves may be azure to metallic blue. Besides the straight species, you will find newer cultivars `Boulder Blue’ and `Elijah Blue,’ with dramatic blue foliage.
Sedum cauticola
Zones 4 to 8
At 2 to 4 inches tall and about a foot wide, this sedum makes a nice carpet under butterfly bush, baptisia, Perovskia (Russian sage) and other tall sun-loving perennials. Rosy pink flowers top the small, fleshy blue-gray leaves arising from purple stems. Plant it with partners that like sunny, well-drained sites such as taller sedums (S. `Brilliant’ or S. `Carl’), penstemon, lavender, blue oat grass, blue fescue, dianthus and sempervivum. It makes a nice combination with compact varieties of coreopsis, such as `Sweet Dreams’ and `Zagreb.’ It creates an interesting edge for patios, sidewalks or driveways where it can trail onto cement or bricks while withstanding the reflective heat.
“These are plants that need good drainage,” says Dan Biernacki of Ted’s Greenhouse in Tinley Park. “They’re great for the xeriscape [dry] garden where nothing else grows. They are low maintenance and require little or no water.” Biernacki notes that good drainage during the winter is crucial to these plants, which can rot easily if they sit in standing water.
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Where to buy
Here are a few sources for sun-loving ground covers:
Gethsemane Garden Center, 5739 N. Clark St., 773-878-5915; www.gethsemanegardens.com
High Country Gardens, a mail-order service of Santa Fe Greenhouses in Santa Fe, N.M., 800-925-9387; www.highcountrygardens.com
Klehm’s Song Sparrow Perennial Farm, 13101 E. Rye Rd., Avalon, Wis., 800-553-3715; www.songsparrow.com
Ted’s Greenhouse, 16930 S. 84th Ave., Tinley Park, 708-532-3575; www.tedsgreenhouse.com
The Fields, 1850 Caton Farm Rd., Joliet, 815-744-7841; www.fieldsnursery.com
The Growing Place, 25W471 Plank Rd., Naperville, 630-355-4000; www.thegrowingplace.com
The Natural Garden, 38W443 Illinois Highway 64, St. Charles, 630-584-0150; www.thenaturalgardeninc.com
White Flower Farm, 800-503-9624; www.whiteflowerfarm.com
