Ground Cover Plants
Every new gardener soon discovers that any soil he leaves bare will quickly be invaded by plants. Some of these may be the children of self-seeding plants he is growing nearby, but more often they will be weeds. If you look under a thick shrub whose branches sweep the ground you will find few if any weeds. Weed seedlings, like any other plant, need light in order to grow: deny them light and they will quickly die. Hence the value of what are known as ground-cover plants.
Any plant, large or small, that effectively shades an area of soil around it for most of the year is a prospective candidate, and many are now valued specifically for their ground-covering abilities. It is the modern way to reduce time needed for garden maintenance. It can also be a most colourful way, especially if low-growing plants are used as ground cover under and around trees and larger shrubs, or over bulbs which will grow through them to the light. But it is not a miracle method: ground-cover plants will not kill off established weeds like couch-grass and ground elder. The first step, therefore, is to dig and weed the area thoroughly, or treat it with a complete herbicide. For the first season or two after planting you must also hoe and hand weed around the plants until they grow together. Thereafter, however, there will be very little weeding to be done.
Many of the bushy and prostrate conifers are expert ground coverers, as are shrubs such as Erica cornea, Berberis thunbergii, the ivies (Hedera), Mahonia aquifolium, and Pernettya mucronata, which have been dealt with elsewhere. Good border plants for this purpose include the lungworts (Pulmonaria), the navelwort (Omphalodes cappadocica), garden pinks (Dianthus), hardy geraniums, day lilies (Hemerocallis), catmint (Nepeta), ice plant (Sedum), and knotweeds (Polygonum).
A surprising number of rock plants excel as ground-cover plants. I do not mean the true alpines, which need a specially prepared site with perfect drainage, but old favourites such as yellow alyssum, white arabis, some of the thrifts (Armeria), rock cress (Aubrieta) in its various hues from purple to pink, some of the delightful rock phloxes, the rose-pink Saponaria ocymoides (easily raised from seed), as well as many saxifrages and sedums. Given reasonable drainage and a place in the sun they will spread themselves on the flat and make a carpet of colour in their season.
Of special importance are those plants that do not insist on a lot of sun in order to flower, or that have coloured foliage. These are the ones that can be grown under and between shrubs and around taller plants. Some of them are well known, like the lily-of-the-valley (Convallaria), whose scented bells appear in spring, and the June-flowering London pride (Saxifraga umbrosa), which makes neat, close-packed rosettes of leaves and bears dainty spires of tiny pink flowers in June. Lady’s mantle (Alchemilla mollis) is a grow-anywhere plant admirably suited to the front of a border. Its soft, pale-greyish green leaves appear pleated at first before opening up into their rounded shape. The tiny sulphur-yellow flowers are borne in loose sprays above the foliage from June to August. Although somewhat subdued in its colouring, it makes an excellent ‘contrast’ plant in sun or partial shade. Its leaf height is about 300 mm (1ft), with flower stems nearly double this.
A lighter touch is provided by the pearl ever-lasting (Anaphalis triplinervis), with its oval, pointed, grey leaves and tiny white ‘ever-lasting’ flowers that bloom for up to three months in summer. It grows about 230 mm (9 in) tall, is partial to moist soil, but must have an open position with plenty of light, where it quickly makes large clumps.
It is hardly surprising that the large, rounded, shiny, leathery leaves of bergenias (members of the saxifrage family) led to these plants being called elephant’s ears. Bergenia cordifolia and its cultivars and hybrids are essentially evergreen except in the worst of winters. Usually deep green in colour, the foliage of some bergenias changes to bronze or maroon in the winter. The flowering season is early to late spring, according to type, when clusters of carmine to pink or white blooms, usually bell-shaped, open on thick stalks. Foliage height is usually 200-300 mm (8-12 in), but is a little less in some of the modern hybrids.
Among plants that are less commonly grown, although they are not so rare as they once were, are the various coloured-leaved forms of the common blue bugle (Ajuga reptans) such as grey-green and white ‘Variegata’; ‘Multicolor’ (’Rainbow’), with leaves that are mottled with yellow and flushed with pink; and ‘Burgundy Glow’, whose foliage is tinted with shades of wine red. All are easy to grow in moist soil and develop the best foliage in light shade. Their spires of blue flowers appear from April to June, but often have a second showing in late summer.
Perhaps at their best when growing in light shade, the barrenworts (Epimedium) spread slowly to make a carpet of dainty evergreen foliage topped with sprays of mostly yellow, red, or pink flowers in mid-spring to early summer. There are several species and hybrids that are garden-worthy. Among the prettiest are E. x versicolor ‘Sulphureum’, which has coppery coloured young foliage in spring and pendulous, pale-yellow flowers, and the Japanese E. x youngianum ‘Niveum’, with bronze foliage and showy white blooms. Most of these plants grow 230-300 mm (9-12 in) tall, although their flower sprays may be considerably taller.
Happy in sun or partial shade, the alum roots (Heuchera) are as good around shrubs as in a front-of-the-border spot. The most common species is H. sanguinea, a hardy perennial which is easily raised from seed, although the colour of the seed-grown plants is not always true to the rosy red of the parents. You can buy a number of named cultivars, however, with flowers from scarlet, through purple-red and pink, to white. The plants form clumps of rounded leaves some 200 mm (8 in) high. The long dainty stems of the tiny trumpet flowers are more than twice as tall and put on a display for months from June; they make good cut flowers, too. Heucherella, a cross between Heuchera and a related Tiarella species, is a similar plant but somewhat larger and more vigorous. Its cultivar ‘Bridget Bloom’ carries a profusion of light-pink flowers in spring and often gives a second show in late summer.
The rose of sharon (Hypericum calycinum), one of the St John’s worts, spreads horizontally by means of stolons (prostrate creeping stems) and is an excellent ground coverer, especially on a bank. The large golden blooms, each up to 75 mm (3 in) across, with a central ruff of stamens, flower from June to September; although the plant grows happily in shade it flowers well only in the sun. It is an evergreen by inclination and the old foliage is best sheared off in early spring before the new growth appears. The rose of Sharon’s method of spread makes it a highly competitive shrub that is inclined to invade the territory of low-growing neighbours -even a well-established lawn – so be careful where you plant it.
Few plants can surpass the perennial candytuft (Iberis sempervirens) ‘Snowflake’ as a ground coverer. It spreads gently by means of underground stems to form a dense mat some 230 mm (9 in) high and as much as 1m (3-1/4ft) across. Its dark, evergreen foliage is effective all the year round and the plants are smothered in dazzingly white flowerheads in May. Apart from being a few inches shorter, the cultivar ‘Little Gem’ is very similar. Both can be increased by means of cuttings or by careful division. It is sometimes suggested that these plants should be grown in sun, but I once grew ‘Snowflake’ for many years in a rather shady spot, where it continued to thrive and flower well.
Creeping jenny, or moneywort, is often to be found in rock-plant lists under its botanical name of Lysimachia nummularia. It is a vigorous evergreen creeping plant that grows almost anywhere in moist soil. Its prostrate stems are lined on either side with small, round, bright-green leaves; golden, buttercup-like flowers open along these leafy chains in June and July. Equally easy to grow is its golden-leaved cultivar, ‘Aurea’, which, although a little less quick-growing, makes a wonderful splash of colour from spring to autumn. In winter the leaves turn to a very light brown colour.
Few foliage plants can outshine the gold-leaved form of our native herb marjoram (Origanum vulgare ‘Aureum’). Its leaf colour is brilliant and when viewed from a distance is frequently mistaken for a patch of flowers. Reaching a height of some 230 mm (9 in), it produces magnificent clumps that remain vivid for most of the year. Its tiny, hardly noticeable purple flowers bloom in July and August.
One of the best evergreen ground coverers for shady areas, Pachysandra terminalis, has toothed, shiny leaves of rich green that give a luxuriant appearance to the area. It carries dainty spikes of white, scented flowers in early spring. Happy in acid to neutral soil, it steadily increases its area of influence by means of underground stems, creating a 250 mm (10 in) thick mat of growth. It will happily swamp low-growing neighbours, but it cannot harm larger shrubs and trees. ‘Variegata’ is a silver variegated form that I find more attractive than the type species.
A plant I value for the contrast its ferny foliage can make with other plants is rue (Ruta graveolens). The colour of the species leaves is grey-green, but in its cultivar ‘Jackman’s Blue’ they are blue-grey and very striking. The height and width of the plants is about 450 mm (18in). These rues are evergreen and prefer a place in the sun, but provided the soil is well drained they do not seem to mind whether it is light or heavy. It pays to cut back the plants in spring to help keep them bushy.
Another attractive evergreen lover of shade is Tiarella cordifolia, one of the foam flowers. Its foliage creates a 100 mm (4 in) high carpet that is green in summer and tinged with bronze in winter. In May and June the plants carry feathery plumes of white flowers above the leaves. Given a moist, peat-enriched soil in the shade of shrubs it can spread quickly – not to say rampantly – but it is certainly one of the prettiest shade flowers. T. wherryi enjoys the same conditions, but is clump-forming, slow-developing, and therefore a less efficient ground coverer. It may, however, be a better choice for a very small garden. The flower plumes of this species are pinkish white.
Among the most useful and best-loved of all ground-covering plants are the periwinkles (Vinca), which grow and flower in both shade and full sun. If you have space to cope with it the variegated form of the greater periwinkle (V. major ‘Variegata’) is the best. Its foliage is well marked with creamy-white and shines out even in a dull spot. The wandering shoots can be several feet long, however, and will scramble over the soil as they lengthen, eventually rooting at their tips. In very small plots, therefore, a better choice is the lesser periwinkle (V. minor) in one or other of its several cultivars, which offer leaves variegated with yellow or white as well as both single and double flowers in plum purple, blue, or white. Reaching some 200 mm (8 in) high, they do creep, but slowly, and are easily kept under control. Their main flowering time is April to June, but you will find that odd flowers open any time from then until the autumn. Although periwinkles are shrubs, when large enough they can be lifted, divided up, and replanted like border plants at any time between September and April.
Presumably on account of its size (I cannot think of any other reason) Waldsteinia ternata is usually listed under rock plants or even alpines. Yet it is a very versatile plant, flourishing in sun or shade, in dry soil or moist. It produces an evergreen mat, some 100 cm (4 in) high, of dark-green leaves which somewhat resemble those of the strawberry, but are smaller. It is a very well mannered plant, spreading but not rampant, and bears sprays of bright-yellow flowers in spring.
Some of the ornamental grasses are also useful ground-cover plants and add colour for many months of the year. I particularly like the old gardener’s garters (Phalaris arundinacea ‘Picta’). It grows well on any soil from sand to clay and, although more luxuriant of growth where the soil is moist, copes very well if it tends to dry out during the summer. What is more it does not mind being planted in a spot shaded by a wall or fence. It is a graceful plant that can reach 1m (3-1/4ft) in height, with stout stalks and white-striped leaves, and is eventually topped with feathery flower plumes. It is not an evergreen, but the dried stems and leaves remain attractive for most of the winter and can be left in place until new growth is due in early spring.
Much shorter at 150 mm (6 in) tall, although the flowering stems can be almost twice that height, Festuca glauca makes neat clumps of bright blue-grey that are as useful for edging as they are planted in bold groups, and provides an interesting contrast with broad-leaved plants. F. eskia is a dark green species that also makes dense ground cover. Both these need a sunny site and well drained soil. Bowles golden grass (Milium effusum ‘Aureum’), on the other hand, is happier in cool soil and shade, where small plants soon make solid clumps. It is particularly effective in spring, when its colour is bright gold. This grass will cast a little seed about, but as all its progeny are golden, too, this is no real disadvantage.
There is no mistaking the relationship of the 300 mm (1 ft) tall Lamium maculatum with the common dead-nettles, owing to the shape and form of its foliage and pink flowers. Its dark green leaves, each with a broad centre stripe of silver, make an interesting display throughout spring and summer. Most striking of all is its cultivar ‘Beacon Silver’, in which the silver area covers almost the entire leaf surface. Having bright yellow leaves, but still with the silver stripe. L.m. ‘Aureum’ stands out well, but is rather slow growing. Both the species plant and the cultivars thrive best in shade and humus-rich soil that does not dry out. Given these conditions they quickly spread to make large mats of growth. Unfortunately, slugs enjoy both these conditions and the plants as well, so slug bait is called for every spring.
The related yellow archangel (L. galeobdolon ‘Variegatum’) is a much more vigorous plant. It has very attractive small silver-marked leaves, but it sends out long trails that rapidly march across the ground and even up among the branches of low-growing shrubs. It is ideal for growing beneath trees, where it will settle down to provide a handsome mat 250 mm (10 in) high, but it is not safe to plant elsewhere unless you are prepared to curb its invasive tendencies.
By careful selection and siting, ground-cover plants eventually create a living carpet of green, grey, silver, yellow, red, and purple foliage that is effective in most cases the whole year round; their flowers can be regarded as a delightful bonus. Most of these plants should be planted about 300 mm (1ft) apart to give quick coverage, and this entails using a lot of plants. However, since most of them root as they spread or make vigorous clumps, they can be divided up every season or two to make more of them until you have sufficient for all your needs. You cannot do this with any of the conifers or with most of the shrubs you use for this purpose, but these do not in any case need to be planted so close together.