Groundcovers for the Garden Designer Gary L. Koll er An eclectic selection of unusual plants for innovative gardeners. With one foot firmly planted in the living col- lections of the Arnold Arboretum and the other in the Landscape Architecture Depart- ment of the Harvard Graduate School of Design, I look at plants for novel uses that may not be fully appreciated by the garden- ing public. I have long believed that the cohe- siveness of a well-crafted garden relies heavily on the successful application of groundcovers. These plants can be used as a "substrate" through which other plants emerge, and which knits the planting into a composition that is visually and spatially pleasing. Given time and the appropriate conditions for growth, groundcovers potentially can reduce the maintenance requirements of the total landscape. Having the opportunity to visit many plant collections as well as developed gardens, I have come across a number of plants that appear to have all the qualities of a successful ground- cover, but are seldom cultivated as such. What are those qualities, you might well ask? Most good groundcovers are little more than very successful weeds controlled and put to good use. The plants not only must maintain them- Epimedium pmnatum var. colchicum in bloom. From in are selves the spot where they planted but the Arnold Arboretum Archives. also must be able to spread outward and colonize an ever-expanding area. With many good groundcovers, the primary concern is not of most volunteer weeds, and tough enough to encourage their growth, but rather to con- to survive neglect, poor soils, and extremes of tain them by installing restraining devices at drought and cold. Groundcovers should main- the perimeter of the space allowed them. tain their foliage in good condition all sum- A good groundcover should be rather low mer long and not die back prematurely, and dense enough to suppress the intrusion leaving a patch of bare earth where late sum- 25 Artemisia stellerana ‘Silver Brocade’ m bloom. Photo by Gary Koller. Anemone canadensis mer weeds can move in. While a groundcover can be either woody or herbaceous, the focus The rapid growth habit of Anemone canaden- in this article will be on less familiar herba- sis leads some gardeners to dub it as "invasive;’ ceous species that deserve greater recognition and I have been cautioned against deploying and testing. As you read about the following it in the landscape. However, it is precisely plants, bear in mind that each one has this trait that enables the plant to make a strengths that can be used to advantage in tight, dense cover and to persist in difficult garden-making as well as weaknesses to be locations. While it may not be a plant for the suppressed. mixed perennial border, it could be used very What follows is a selection of plants that appropriately in challenging areas: beneath I am still learning about and that seem to have trees and shrubs, or in locations where it can a bright future as groundcovers for our be contained by barriers that restrict its gardens. I hope that one or more of them may spread. be unfamiliar to you, and that I may entice I can envision this plant being used to good you into acquiring them for testing under your advantage in parking islands, between side- own growing conditions and maintenance walks and buildings, and in urban parks to fill regime. My comments are offered here in the in empty spaces that invite weeds. The small spirit of challenge-to encourage you not only white flowers in early summer persist for to keep an eye out for plants with unusual var- several weeks and are charming if not spec- iations but also to experiment with nontradi- tacular. The attractively lobed foliage remains tional uses of these plants. I welcome hear- green and in good condition all summer long. ing from any readers who might know of This anemone might be improved by the similar plants that deserve wider recognition. selection of compact forms with darker green 26 foliage and a longer flowering period. There with pale yellow variegation in the leaves. is also the possibility of hybridizing Anemone There is some question whether this is a canadensis with other anemones to extend natural variation or a population with a virus. the floral color range, the season of bloom, or If, however, some types are discovered with the spreading tendency. A. canadensis is often good stable variegations, they would be a compared to A. sylvestris, a plant that blooms definite plus for the shade garden. Horticul- several weeks earlier, but one I find a weak ture can be enriched by observant individuals grower under those conditions where A. combing wild plant populations for canadensis thrives. individuals with traits for use. _ superior garden Once found, the plant needs to be propagated Artemisia stellerana ‘Silver Brocade’ and evaluated under different environmental Parched, sunny growing conditions present a conditions. If the plant maintains its unique challenge in many areas of the country. characteristic and is garden worthy, it can then Artemisia stellerana is one of those plants be publicized and distributed. that loves to bake in the sun and that natur- takesimana ally inhabits sand dunes and poor soils. A Campanula native of Asia, it has naturalized itself on This campanula is familiar to only a few dedi- beaches from Quebec to Virginia where it cated perennial gardeners, who mostly use it holds and stabilizes the shifting sand. The cul- in the mixed border. Spreading at a deliberate tivar ’Silver Brocade’, a recent introduction of pace, it forms sizable colonies over time, and the University of British Columbia Botanical because of this tendency, it seems well Garden, was selected for rich gray foliage, a adapted to use as a groundcover. The leaves more finely cut leaf, and a lower, more com- are roughly heart-shaped with attractive, scal- pact growth habit. In the landscape, it can loped edges. The flowers are produced in large look beautiful edging a bluestone path where terminal panicles, which rise out of the basal it has the opportunity to spread out and soften cluster of leaves to a height of 30 to 60 cen- the hard lines, while at the same time echo- timeters (12 to 24 inches). Because of the num- ing the blue-gray color of the stone itself. In ber, weight, and size of the individual flowers, coastal New England, this plant is one of the the inflorescence has a tendency to arch over. best choices for the harsh environmental Individually the flowers are tube-shaped, and assaults encountered by the dunes along the range from a pale, pink-beige to ivory, with ocean. chocolate or bronze markings on the inside of the blossom. If flowering stems are cut back Asarum canadense as the blooms fade, the plant is capable of Few plants tolerate drought and moderate flowering two or three times a summer. This shade as well as the Canadian ginger. It grows tendency to rebloom varies directly with the naturally in the understory of woods in Ohio, amount of light available. Repeat flowering Kansas, and Missouri where it forms diffuse, also appears to be dependent on soil moisture, but widespread colonies. In cultivation and for in extremely dry seasons I have observed with some level of attention, it stays dense that these plants flower less frequently. In any and displays a beautiful moderate green case, I have found that the foliage itself is foliage all summer long. It combines naturally quite drought-resistant. with ferns and other woodland plants. In the Carex siderostricta future, this plant could be improved by some ‘Variegata’ selection for more vigor and darker colored In northern landscapes (Zones 5 and 6), Carex foliage. siderostricta ’Variegata’ has the potential to be James Waddick of Kansas City, Missouri, used much as Liriope muscari ’Variegata’ is recently took me to see a wild population in the south-except that its greater cold 27 ~ ----- ~ --,-,- The fohage of Campanula takesimana. Photo by Gary Koller. hardiness is accompanied by a deciduous where. Barry Yinger, a noted collector of habit. Carex siderostricta ’Vamegata’ forms Japanese plants, tells me that, while there are broad clumps of cream-colored variegated several mediocre forms in terms of degree of foliage, which stand 20 to 30 centimeters tall variegation, a spectacular form is available (8 to 12 inches). It thrives in light shade and from Watanabe Nursery. soils that vary from dry to moist. In extremely While I am not aware that they exist yet, dry locations, I have noticed the white mark- would it not be desirable to select ings of the leaves will assume a tired, epimediums for unusual leaf types, for richer, brownish cast by late summer. This species more saturated, autumn foliage colors persist- mixes well with hosta, astilbe, and ajuga, ing into wintertime, or for foliage marbled forming tapestries of foliage texture and color. with contrasting colors of green? We need to seek out new forms actively and introduce Epimediums them to the gardens of America. I’ll be the first Few plants are as tough, dependable, and per- in line to purchase them. sistent in shaded landscapes as the various species and cultivars of Epimedium. These Liriope muscari plants could be made more useful by the Southern gardens are rich in many forms of introduction of variegated types, which lily turf, which allow for numerous creative presently exist in Japan and perhaps else- applications of this attractive groundcover. In 28 realized that plants with huge leaves and great stature could provide visual excitement and spatial illusion for smaller landscape spaces.