The role of the ground cover category of ornamental plants and its’ place in the built landscape is a murky subject at best and is downright confusing for most gardeners. What are they, how to use them, and why would one ever want them is a question that many gardeners ponder. When referring to groundcovers one often gets a blank look, or hears about Junipers and Ajuga. That may have been the case before 1970, but the world of groundcovers is so much broader than this that it’s time for an overhaul of the subject. The perennials and ornamental grasses revolution of the 80’s, and the native plant recognition of the 90’s, and the New American Garden development of the millennium with all the new species of low growing spreaders, as well as new forms of Roses, Spiraeas , Forsythias and other traditional shrubs has changed all our old conventions.
Groundcovers used be considered one of the five layers of the living landscape; Trees, Shrubs, Flowering Perennials and Grasses, Groundcovers, and Bulbs. That view considers that all those other layers are separate and distinct; the reality is that the boundaries are blurred, and in the real world, many shrubs with woody stems and persistent aboveground bodies perform the duties of a groundcover, as do the masses of hardy perennials or the prairies of grasses and forbs.
A groundcover is any species or material that serves to inhibit the invasion of an area by the disturbance adapted species we call weeds, or that protects the soil from erosion. This includes lawns, monocultural beds of spreading species like Ivy or Ajuga, densely planted areas of hardy perennials like Astilbes or Hardy Geraniums, mixed species plantings including flowering and foliage plants, low growing shrubbery or conifers, replications of forest understory or salvaged transplant mats of wild plant populations. It can also include mineral layers like sand or gravel, crushed glass, wave washed pottery fragments, and organic materials like shredded bark, compost and leaf mulch.
We look at many styles of landscapes to find the one that appeals to our needs and tastes. The established campus style landscapes with their serene sweeps of uniform textures, contrast with cottage garden beds filled with so many species that they overflow each other in their rioting. Some are severe with isolated specimens in a vista swept clean of competition or support; some are tidy with rows of cultivated individuals and surrounding soil kept cultivated. These are complimented by a neighbor’s home with lawns and herbaceous borders against trimmed hedges, and bordered by another with gravel beds and specimen boulders. Each of these and a thousand others addresses the needs of the landscape in its own way.
Look at the big, beautiful, uncontrolled world, and you see the seamless carpet of uninterrupted beauty rolling on in every direction. There are trees, shrubbery, flowering perennials and a carpet of green that covers all the soil and creeps up the rocks and drools over into the creek edges. There are no interruptions, no objectionable presences, and no note of disturbance until a road, a house lot, or an erosion scar interrupts the harmonious scheme and the tapestry is disturbed. Once bare earth is exposed and opportunity for colonization is offered, there is place for those species evolved for rapid occupation of unoccupied soils.
These species have a few characteristics in common; they spread rapidly, reproduce easily, mature early, and produce abundant offspring. They are the Band-Aids of the earth, created and developed to cover the vulnerable bare places, to bind the soil to the site and to exult in their successes by producing as many copies of themselves as possible. These are generally rough, tough plants, and we look at them as less desirable in our domestic spaces than the ones we have chosen. These special plants are pejoratively known as weeds, and we designate them as being the undesirable ones.
Most gardening and landscape problems are design problems. The landscapes we develop are usually simplified versions of natural ones we observe, mixed and blended from sources worldwide, but generally these gardens are responses to situations we encounter. We build homes in a forest, or along a shore, or in grassland, and our first step is to clear away the native plant communities, then to excavate the organic soils that would not support our buildings. The fact that they are required to support the existing landscape is overlooked or ignored and the building sites are filled with sterile mineral soils. These are compacted, graded and drained so they will remain stable, and their very lack of vegetation is one of the criteria used to choose these fill soils.
When we look off at the wild Alaskan landscape we see a layer of shrubs or grasses, this is usually Blueberries and Menzetia mixed with ferns, the shore edging wetland grasses, or the meadows of mixed grasses, sedges and flowers. The beauty of the scene is so overwhelming that we often fail to analyze the combinations. Once we look with a deconstructivist eye, we can see that the reason it appears so unified is that our eyes stop penetrating at one of the layers. There is almost always another layer or two below the one we are looking at, but who cares? We can’t see it so we don’t pay it any attention. In the world of the earth scientist or the soil microbiologist there are so many other layers that we could proceed down for hours, but as landscape scale workers and designers we need only concern ourselves with the limitations of a casual glance.
Landscape design is much like set design for the theater or movies. We suggest a scene, providing the guidelines and some key elements, and the participant provides much of the rest. We show icons of ornamental trees, a selection of flowering shrubs or a combination of conifers highlighting some sense of repetition or contrast and tie them together with a web of common foreground and we have a landscape. Each person who experiences the setting will carry off another individualized response; our job is to make sure that no disturbing elements thrust themselves through the skin of our illusion to disturb the viewers’ sense of well being. That is where the choice of groundcover will be felt the most clearly.
Large scale designs, with vistas that include full views of mature trees will call for a larger size ground cover, it may be as large as the mounding humps of ‘Roseum’ Rhododendron and Mugo Pine planted as a screen. Moving closer and smaller in scale, those elements, those 6 to 8 ft Rhododendrons and Pines will need a groundcover of smaller shrubbery like Spiraea ‘Little Princess’ and Viburnum trilobum ‘Compacta’ at about 2 ft. Closer still and smaller in scale, an 18 inch groundcover of Epimedium or Catmint will serve, and under them as we get smaller and closer still we can use ground hugging Lysemachia ‘Creeping Jenny’ or Creeping Canadian Dogwood, Cornus canadensis.
The scale we work at determines the size of the groundcover we choose, and the same area can be viewed at several scales at the same time. There are many landscapes that borrow larger vistas from the surrounding scenes, and as we ratchet our view down, closer and closer we can focus on smaller and smaller scale plant combinations.
There is also the element of time to consider, landscape creation works in the three dimensions of all other design, but it also works with the passing of time, the change of season, and the change that works in the world. Imagine a slope in the front of a home, supported by largish stones, clustered irregularly and half buried in the soil to mimic a naturalistic mountain scene. Snow melts off and the first spring flowers emerge, tiny Primroses, tips of Crocus and the first Snowbells. Flowers burst out within an inch of the soil; it is still so cold that there are very few plants emerging from dormancy. There is no competition, no weed pressure, and carpets of Primula juliana are sufficient to cloak the soil.
Two weeks later, and the first ‘Pom Pom’ Primula denticulata are showing, flowers first but quickly followed by pointy crystalline edged leaves of pale green. By the time they have gotten eight inches tall, there is a carpet of young grasses or chickweed sprouting up around the bottoms of the Primroses. This is the time for the carpeting effect of the Purple or White Rock Cresses, they will overgrow the invaders, and we will have our treasured Primroses with a beautiful bed of bloom sheltering them. The Daffodils emerge, under planted by Astilbes, and as the golden flowers of the Narcissus fade, the emerging ruddy ferny leaves will not only provide weed cover, they will also conceal the fading stalks of the spring bulbs, and they look so nice with the early blooming Globe Flowers.
The secret to remember when planting a full season floral display is that many plants can occupy the same ground space over the space of the growing season. As they come into and pass out of bloom their physical shape changes, stems rise and fall, blossoms open and close, and the heavier seed pods pull the stems downwards. The earlier blooming species fade back as the later emerging ones come up, our same slope with the half buried boulders can be home to Columbines, Campanulas, Shasta Daises, Bee Balm, Irises, Delphiniums, Lilies and Rudbeckias as the season progresses.
Just as we design our flower beds for maximum floral display, we can do the same for the larger landscape; our layers of interest can change over the season. A bed featuring some of those new Yakusimaina Hybrid Rhododendrons like “Yaku Princess” can start the season with a carpet of early bulbs, something small so they will be in scale with the shrubbery, like deep blue Muscari and dwarf “Tete a Tete” Narcissus. As the bulbs fade, a layer of Epimedium rubrum emerges, the deep bronze leaves seem to leap up out of the ground in a week, and each plant gets two feet across, with dozens of delicate arching stems of tiny columbine-like red and yellow flowers. The Epimedium makes a great combination with the fuzzy grayish green leaves of the Rhododendrons, and get large enough that any weeds that would like to show up are hidden.
Carrying on from the Rhododendron group, and linking them to another planted area we could use a layer of the low growing Spiraeas, something twiggy with lots of stems and thousands of small leaves. I love the bright green “Limemound” or the gold and red “Goldflame”. These will get about two feet tall and three feet wide, so if they are planted on 3 ft spacing, they will grow into a single mass. They can be purchased as 4 inch pots in the spring, or as bare root starts pretty economically.
Look at the landscape around Eaglecrest, the rolling dwarf Blueberry, Fern and Menzetia shrubbery carpeted with Dogwoods, Low Bush Cranberry, Crowberry, and Nagoon creates a complete picture. That model will serve us extremely well. We can vary the species as our design demands, but the shapes and final group form is an extremely attractive result.
Bark mulch, compost, or shredded evergreens from the tree services work as temporary covers; they cover the soil, provide a uniform background and protect the bases of the larger shrubbery and trees as they get established. They are an expensive and laborious long-term solution for an established landscape, and should be looked upon as a temporary phase. They do the job while the living groundcover layer is getting established. There is also the worry that bark mulch will be heaped up around the trunks of the trees and shrubs as a weed control effort, resulting in crown fungus infestations.
Groundcovers are an essential part of the home or commercial landscape; they lower maintenance efforts, control soil erosion, suppress or conceal unsightly invasive species, and provide the background for our featured performers. The groundcover layer can also provide a changing colorful display, co-coordinated with the larger plants in our designs. Designed as integrated components in a planting scheme, they will remind us not to bash the trunks of our trees with lawn mowers or weedeaters, direct traffic along preferred routes, reduce inputs as far as soil enhancements and drainage efforts go, and complete the spaces we create as stages in the theater of our lives.