Lee Valley & Veritas Gardening
Newsletter
Lee Valley 35 Years  
  Volume 8, Issue 8 - August 2013    
 
Groundcovers: The Glue of the Garden
Lamiastrum
Variegated groundcovers such as Lamiastrum brighten up a shade garden.
 
Groundcovers are landscape workhorses that serve both practical and design-related functions in the garden. In terms of practical functions, they provide an alternative for covering steep slopes where mowing grass would be hazardous. They also retard soil erosion, suppress weeds, and shade and cool the soil. When planted around the bases of trees or parallel to tree roots that have come to the surface, they guard against grass-trimmer and mower damage. They can even deter animals; I've seen prickly pear cactus (Opuntia humifusa) used as a groundcover around the base of a building to ward off cats and dogs. Groundcovers can also act as splash guards to prevent soil-borne fungi from getting onto the foliage of other plants, such as roses. There are dependable groundcovers for sunny and shady areas, wet and dry soils, acidic to neutral soils and even windy spots. They function as living mulch, thereby saving you time, money and effort.
 
Creeping phlox
Creeping phlox makes a great filler in rock outcrops and rockeries.
 
In terms of design functions, groundcovers join together the different areas of the garden. They also link different plants (shrubs, trees and perennials) in coordinated compositions. Visit a Japanese garden and see how sheets of moss provide a continuous carpet for azaleas, ferns and pines. Groundcovers also establish line and form to lead our eyes around and through the garden. This is enhanced by using finer textured groundcovers as background plants. Another one of their design functions is to act as living curbs that define various garden areas and give them a finished look. Groundcovers such as sedums, creeping phlox (Phlox subulata), thyme and various rock cresses (Arabis spp.) serve as gap plants by filling cracks and crevices in rock outcrops and rockeries. Furthermore, groundcovers make excellent foils and screens, reducing the scale of logs and stumps, softening the bases of garden statues and masking the ripening foliage of spent bulbs.
 
Woodland phlox
The fragrant blooms and glossy leaves of hardy epimedium
 
Due to their variety of form, foliage and flowers, groundcovers make excellent partners in plant combinations. In my shade garden, I rely heavily on the white blossoms of foam flower (Tiarella cordifolia) combined with perfoliate bellwort (Uvularia perfoliata) and also woven through barren strawberry (Waldsteinia fragarioides). Foam flowers make an attractive companion when planted beneath yellow-flowering, shade-tolerant Japanese rose (Kerria japonica) or with woodland blue phlox (Phlox divaricata). The leaves of variegated groundcovers, such as the Lamiastrum and Ajuga species, act as flashlights in the shade garden. For appealing texture and form combinations, try Bergenia species with Heuchera, and ferns and hostas with ivies. On hot dry slopes, I like one of the many spreading strawberries (Fragaria spp.) planted with thyme and ajuga, or with thyme and barrenwort (Epimedium spp.).
 
Bergenia
Lovely Bergenia adds some eye-popping color to the garden.
 
My broad and flexible definition of groundcovers includes various shrubs, vines and ornamental grasses. I also include taller plants that spread and coalesce, such as May apple (Podophyllum peltatum), Solomon's seal (Polygonatum spp.) and various ferns. Low-growing compact junipers, such as creeping juniper (Juniperus horizontalis), particularly 'Plumosa Compacta', 'Prince of Wales' and 'Wiltonii', are worthy candidates for sunny, drier sites. Cascading shrubs such as weeping forsythia (Forsythia suspensa), rockspray and cranberry cotoneaster, and various euonymus species are ideal for creeping over the edges of rocks, walls and planters. Ornamental grasses such as the spectacular Japanese blood grass (Imperata cylindrica 'Red Baron') and the pin-cushion shaped blue fescue (Festuca spp.) make excellent groundcovers bordering a path or edging a border. Two groundcovers that have done particularly well edging the scree beds of my Toronto, Ontario, garden (Canadian hardiness zone 6) are black mondo grass, with its ebony leaves, and prairie smoke (Geum triflorum), with its pink feather-like hairs. Turf is also a useful groundcover that imparts neatness and order, provides a place for children to play, and acts as a stage to offset the vertical planes of the house.
 
Prairie smoke
Prairie smoke makes a terrific groundcover bordering a path or edging a border.
 
Many vines, devoid of support, will spread across the ground to act as a cover. Consider Virginia creeper (Parthenocissus quinquefolia), chocolate vine (Akebia quinata), trumpet vine (Campsis radicans) and climbing hydrangea (Hydrangea anomala subsp. petiolaris). One of my favorites, winter jasmine (Jasminum nudiflorum), flowers in my garden in January and early February, and even saves some blooms for April. It roots where the nodes on the underside of the leaves come into contact with the ground, thereby producing inexpensive offspring. Take note, however, that some of these vines can become pesky (for example trumpet vine) and can pop up from root runners where you least expect them.

Concern about groundcovers running amok and overtaking the garden is certainly warranted. Goutweed (Aegopodium podagraria), lily-of-the-valley (Convallaria majalis), bracken fern (Pteridium aquilinum), chameleon plant (Houttuynia cordata), stonecrop sedum (Sedum acre), silverweed (Potentilla anserina), ribbon grass (Phalaris arundinacea) and blue wild rye (Elymus glaucus) can spread readily, crowding out other plants in their path. There may be places where you can take advantage of these rapid spreaders though, such as an area with exposed road cuts, a site with severely compacted soils, or a space under the skirts of spruce trees. Be warned though — where these plants are not wanted their removal can be challenging, since root pieces and seeds left behind readily produce offspring. At cottage properties in particular, groundcovers such as Japanese spurge (Pachysandra terminalis), Vinca and various ivies can quickly make inroads into forested areas to the detriment of the native flora.

 
Chameleon plant
Be wary of invasive groundcovers such as the chameleon plant (above).
 
Before purchasing groundcovers, use your scaled landscape plan and plant-spacing tables to calculate the number of plants required. Closer spacing does necessitate buying more plants, but they will merge more quickly and fend off weeds more readily. You can offset the higher cost by buying rooted cuttings in bulk, as opposed to individual potted plants. When planting groundcovers, particularly shade-tolerant ones, a fairly rich compost-fortified soil will help speed their establishment. Annual maintenance is modest and varies with the plants selected. Some, such as Japanese spurge, Vinca, ivies, fiveleaf aralia (Acanthopanax sieboldianus) and cotoneaster, may creep too far and start smothering neighboring plants. Prune back the offending plants with hedge shears to keep them within bounds. Ground-hugging plants can be subject to crown rot, various diseases and damage by ever-present slugs and snails. Lay pea-gravel mulch in sunny locations and bark mulch in shady ones to help keep the crowns drier. The mulch also insulates against winter temperature fluctuations that can cause root heaving. Bring slugs and snails under control by using various baits, traps, copper strips, etc. Leaf mulch could be applied in late fall to further protect evergreen groundcovers such as Japanese spurge, barrenwort, ground dogwood (Cornus canadensis), partridgeberry (Mitchella repens) and ivy from winter foliage dieback. With the onset of warmer spring weather, remove this insulation blanket a bit at a time. Older plants should be divided if their centers have dieback and new growth is directed to their perimeters only.

In conclusion, you really can't go wrong if you stick with groundcovers, the glue of the garden.

Text by Frank Kershaw

Photos by Marnie Wright

Frank Kershaw is an award-winning horticulturist with more than 35 years of experience. He teaches garden design and horticultural courses at George Brown College in Toronto, Ontario, and at the Toronto Botanical Garden. Frank is also a presenter at the Lee Valley seminars at the Toronto stores.

Marnie Wright (gardenwright@muskoka.com) is a lifelong gardener, writer and passionate garden photographer. Her Rocksborough Garden, developed over 30 years, is located in Bracebridge, Ontario.

 
 
 
 
     
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