It is said that nature abhors a vacuum. Nothing illustrates that dictum better than a patch of bare earth. Left to its own devices, an open, unplanted space in the garden will be quickly colonized by weeds. To keep those areas looking good, we turn to groundcovers. Perhaps the most ubiquitous one used by landscapers in our area is bark mulch. Every spring there is a ritual of spreading shredded bark over beds and borders in an effort to create a weed-free perfect chocolate brown backdrop for trees and shrubs. Gardeners often long for less sterile groundcovers, something with more life and interest than a sea of shredded bark. Many plants, used en masse, can be used as groundcover, but generally plants considered good groundcovers have the following attributes:
• low growing (maximum height of less than 24 inches)
• vigorous and spreading without being invasive
• sufficiently dense to inhibit the growth of weeds
• extensive root system to minimize soil erosion
• relatively low maintenance
• provide multi-season interest
• create unity in a landscape design
Most gardeners are familiar with the "big three" groundcovers -- English ivy, Japanese pachysandra and periwinkle (Vinca minor). These are readily available and time-tested, but there are many excellent plants to try if you're ready to move beyond the ordinary and add some pizazz to your garden.
For sunny areas
• Plumbago (Ceratostigma plumbaginoides) ---- A low growing perennial that gets 9 to 12 inches tall with a spread of 12 to 18 inches. The leathery, oval leaves are topped with gentian-blue flowers in late summer. In the fall, the foliage changes to a beautiful, burgundy-red color. It grows best in rich, moist, well-drained soil. This is an excellent groundcover with multi-season interest for sunny to part-sunny areas.
• 'Tom Thumb' cranberry cotoneaster (Cotoneaster apiculatus) -- This compact, low-growing, deciduous shrub grows 1 to 2 feet tall and spreads 3 to 6 feet wide. Small, light pink flowers top the dense, shiny green foliage in spring. Fall foliage is a brilliant red. Grow in average, well-drained soil. This shrub is an excellent choice for cascading over a wall, or adding interest to a hilly area.
• St. John's wort (Hypericum calycinum) -- A stoloniferous sub-shrub that grows 12 inches tall and 24 inches or more wide. In summer, the leathery, rich-green leaves are topped with large, five-petaled, yellow flowers that have numerous, bushy stamens with reddish anthers. Grow in average, well-drained soil. St. John's wort is an excellent groundcover for naturalized plantings or stabilizing hillsides.
• 'Rose Carpet' Chinese indigo (Indigofera pseudotinctoria) -- A low-growing shrubby plant that reaches a height of 8-12 inches, with a spread of 2-4 feet. Rose, pea-like flowers form in summer and continue intermittently into early fall. Grow in average, well-drained soil. This groundcover can be used on slopes, open woodland areas, mixed borders or foundation plantings.
• 'Gold Strike' creeping juniper (Juniperus horizontalis) -- This prostrate shrub grows 6-8 inches tall and slowly spreads 4-6 feet wide. The striking foliage of this juniper emerges bright yellow in the spring, matures to gold over the summer and takes on coral tones in the fall. Grow in average, well-drained soil. 'Gold Strike' makes a dramatic statement growing in a sunny rock garden.
• 'Dark Dancer' white clover (Trifolium repens 'Atropurpureum') -- This spectacular groundcover has purple-black, green-edged, clover-shaped leaves that are topped with white flowers in the summer. Grows 3-6 inches tall and 12-18 inches or more wide. Grow in average, well-drained soil. Beautiful in and around patios, along pathways, around ponds or in a rock garden.
For shady areas
• 'Ice Dance' variegated sedge (Carex morrowii) -- This evergreen sedge grows 12-15 inches tall and quickly spreads to 18 inches or more wide. The stiff, grass-like foliage is dark green in the center with a bright-white border. Grow in average, moist, well-drained soil. The form and texture of 'Ice Dance' adds a nice dimension to a shade garden.
• 'Crimson Fans' red-leafed mukdenia (Mukdenia rossi) -- This unusual groundcover is a slow-growing, clumping perennial that reaches 8-12 inches tall and 12 inches or more wide. Its large leaves sport 5-9 sharply-cut lobes and emerge dark green, marked with bronze, in the spring. Also in spring, bell-shaped, white flowers top the foliage. As the season progresses, the bronze coloration changes to a rich-burgundy color. Grow in rich, moist, well-drained soil. The texture and color makes a beautiful addition to a woodland garden.
• Allegheny pachysandra (Pachysandra procumbens) -- Our native pachysandra is much more elegant than its Japanese counterpart. A clump-forming, semi-evergreen perennial with beautiful, pewter-green foliage, the plant grows 8-12 inches tall and has a slow, spreading habit. In the spring, fragrant bottlebrush-like white flowers are borne on 2- to 4-inch spikes. When fall arrives, the foliage takes on a beautiful, mottled-silver coloration. Grow in average, moist, well-drained soil. This native is an excellent choice for a woodland garden and pairs beautifully with ferns.
• 'Silver Shimmers' lungwort (Pulmonaria) -- Who can resist the beautiful lungworts? This eye-catching perennial has silver-plated leaves with speckled margins. In spring, the pink buds open into platinum-blue flowers. 'Silver Shimmers' grows 6-12 inches tall and spreads 1-3 feet wide. Grow in rich, evenly moist, well-drained soil. The light foliage makes a stunning addition to the dark recesses of a woodland garden.
• 'Heronswood Mist' foamflower (Tiarella) -- The foliage of this clumping perennial is a light green with a cream frosting, topped with pink highlights. In spring, light pink flower spikes are formed. The plant grows to 12 inches tall with an equal spread. Grow in average, moist, well-drained soil. Because of the beautiful foliage color, this is a nice groundcover to illuminate a shady area.
• 'Illumination' creeping myrtle (Vinca minor) -- A cultivar of periwinkle, its beautiful leaves set it apart from its common parent; the leaves are bright gold and edged with a border of irregular green. Like its parent, this evergreen groundcover sports blue flowers in the spring. It grows 6-12 inches tall with a continually spreading habit. Grow in rich, moist, well-drained soil. It is a beautiful plant to integrate into a shady woodland garden.
Judging from many landscapes, one would think that "the big three" are the only groundcovers to be found. There are myriad choices of interesting plants that will add beauty and distinction to your garden. There will be some maintenance, such as weeding and soil preparation, to get groundcovers established. However, over the life of a garden, live plants are more economical and attractive than bark.
Steve Piskor is a Penn State master gardener and Pennsylvania certified horticulturist. Columns by master gardeners will sometimes appear in place of the Garden Q&A by Sandy Feather, a Penn State Extension educator.