Ground-covering plants

Plants that creep, crawl and spread over the earth like a warm quilt are called ground cover. They are the fine linens of the landscape. Insulating in winter and sealing in the earth’s cool moisture in summer, these living blankets have an important place in the garden. Underplanting with bulbs and spring ephemerals brings ground cover to life; in designer’s terms, it can be a unifying element that reduces the contrast between disparate structures and textures. Functionally, they can be used to soften the edges and angles of hardscape and delineate garden or border edges, much the way a hedge does.

Ground cover is also excellent for protecting bare soil. A dense covering of plants can stabilize soil, reduce erosion, discourage the growth of weeds, and grow where other plants cannot and should not grow. The 3-foot to 4-foot area adjacent to a house and beneath the roof overhang — called the “no-grow zone” — is an excellent spot for ground cover. Although it’s commonly planted with traditional foundation shrubs, many of these tend to take a beating from the incursions of home maintenance, utility-meter readers, and the typically unbearable growing conditions. As a result, these plants often die out. Close-to-the-house ground cover is an excellent solution to these situations; it also helps direct rainfall and run-off away from the foundation.

Other portions of the home landscape that are well suited to ground cover include hard-to-maintain areas and those too small to accommodate larger plants: small patios, courtyards, narrow strips between paved areas or walls, patches underneath garden ornaments or amenities, and the ubiquitous steep slope. Ground cover is very compatible with tree roots and can easily be planted in place of a mulched tree ring. Besides providing protection from foot and mower traffic, shallow-rooted plants help break up the soil, making more oxygen and water available to larger tree roots. And the organic matter produced from the annual debris of fallen leaves, twigs, flowers and fruit enhances soil fertility. Although the larger and shrubbier kinds of ground cover can conceal this material (thus reducing cleanup time and cost), the more herbaceous varieties will benefit from having leaf litter removed before spring growth begins.

This brings us to the myth that ground cover is the solution to all things. Like all plants, ground cover requires up-front care and attention to get it established and growing. Picking the right plant for the exposure, soil type and sun/shade conditions at a given site is vitally important. Amending the soil and addressing drainage issues will be critical for quick root growth and long-term health. Mulching at planting is a must, to help maintain soil moisture and reduce the pressure from competing weeds. And of course, there’s no question about the need to water after planting and during periods of drought.

Accordingly, some folks take the “easy route” and sow grass instead. I call this a big mistake! Although grass is less expensive up front, maintaining it will cost more in the long run. And while ground covers may take longer to establish and aren’t totally maintenance-free, they certainly require less care than grass over the long haul. Besides, why choose a boring green-all-the-time grass when you have a colorful array of other options?

The term ground cover can mean many things: Plant enough of anything and you’ll get cover. Traditionally, when we think ground cover we think evergreen, low-lying, spreading plants like vinca and English ivy. In fact, these are two plants to avoid unless you place them in small, contained areas. Even then, controlling them can be difficult — they’re tenacious! Ripping them from the ground is tough, and using herbicides on their slick evergreen leaves is next to impossible. It’s best not to torment future gardeners by planting something that will get out of hand when you can go with a more civilized alternative that makes containment one of the more delightful aspects of gardening. It goes without saying that Japanese honeysuckle and crown vetch are definite no-nos.

Depending on the site requirements, there are many, many options for ground cover. In fact, the most limiting factor will probably be your own definition of groundcover. Woody, herbaceous, succulent, grassy plants that are evergreen, semi-evergreen or deciduous with shrubby, vining, sprawling, clumping growth habits are all good contenders. A few of my favorite kinds of ground cover for the garden are sweet woodruff, bugleweed, green and gold, barrenwort, foamflower, creeping phlox and both Allegheny and Japanese pachysandra. There’s a lot of variability within this group alone offering a range of winter interest, fragrance, seasonal flowering display, and interesting textures and forms. These creeping and spreading ground covers make it easy to dig out individual plants around the edges to introduce in new places or fill in the holes. There’s nothing like a carpet of foamflower or sweet woodruff to give a warm spring welcome!

Ferns, grasses and sedges broaden the spectrum of usable plants. The clumping forms of Christmas, ostrich and cinnamon ferns create a nice presence in the garden. Christmas fern is semi-evergreen through the winter, and the other two are quite impressive once hit by a hard frost. They don’t fit the traditional definition of ground cover, but when planted en masse — wow! On the other hand, New York and hay-scented ferns are active spreaders, beautiful after a light frost and perfect for a woodland-garden setting. Some grasses, such as prairie dropseed, fountain grass and feather reed grass, tend to clump and don’t do a good job of stabilizing loose and exposed soil while they’re getting established. But when planted closely in sufficient mass with a light mulch, a very good cover can develop. For hard-to-maintain slopes, hydro-seeding with a meadow mix of grasses and perennials is an excellent possibility to consider. This gives a wild and natural look, and once established, it’s much easier to maintain than a monoculture of creeping junipers. Grasses such as weeping love grass, little bluestem, Indian grass and switchgrass are just a few to consider. The sedges are a fun and tough group. It’s important to select according to the soil moisture of the site: Some like it dry, and some like it wet. Palm, plantain-leafed and the black-flowering sedges are just a few that demonstrate the variability this plant group has to offer. In fact, the number of varieties of ferns, grasses and sedges alone will keep even the most industrious plant-collecting gardener busy for a lifetime.

The last group of ground-covering plants is the often-overlooked shrubs. These include low-growing, sprawling, arching, multi-stemmed plants that, en masse, create dense cover and are in fact very suitable for steep slopes and cut-and-fill areas. Hypericum, memorial, meidiland or rugosa roses, cotoneaster, forsythia, sweetfern and fragrant sumac are a few worth noting. Planted close enough together and watered and maintained during the first year, any of these will get off to an excellent start. It will be only a matter of time before these sprawlers and spreaders cover the ground nicely.

Given the abundant opportunities within the world of ground cover, it’s wise to: keep it simple (choose one to three varieties, depending on the size of your garden; mixing too many different types will make it too busy); plant companionably (don’t plant two kinds of ground cover with varying growth rates — an English ivy thug will quickly outpace the more refined sedum); remember sun, shade and soil requirements (for both the site and the plant); and finally, be patient. Ground cover doesn’t usually move as fast or work as thoroughly as many of us would like. But then we tend to forget that we’re really just working toward developing the finest linens available for covering sweet Mother Earth.

[Alison Arnold is director of horticulture at The North Carolina Arboretum. She can be reached at: aarnold@ncarboretum.org.]