Choosing and growing grasses
Grasses have been much taken up by garden designers in the last decades, and gardeners are using them more and more, too. Grasses give a wonderful sense of mobility and beautiful, gentle sound in the garden, and they are wonderful with perennials in a border, as part of a prairie planting, or even in containers. The quality of their flower- and seed-heads is enhanced when they’re back-lit by the sun, and persisting seed-heads look entrancing when frosted. They give value and interest for months, with long-lasting spikelets (flowers) and equally valuable foliage.
There are cool-season grasses, which flower by midsummer, and warm-season grasses, which flower in late summer or autumn. Some are fluid and loose, and some are structural, architectural plants; some are evergreen, and even those that aren’t make attractive ‘skeletons’ in the winter, especially lovely when frosted. They are not all green, either – there are beautifully coloured and variegated grasses. Most like to be in full sun, but there are some that thrive in shade, and there are others that will cope with coastal exposure. In short, there’s a grass for every garden, small, large, courtyard, patio or balcony.
Large specimen grasses
For bigger gardens, some large grasses, like evergreen Pampas grass (Cortaderia selloana), make wonderful specimens, especially when grown with a deep green hedge behind it to show off its mound of arching leaves and enormous, silvery, feathery plumes. For smaller gardens, there is a more compact form (C.s. pumila) and there is also a pink-flowered form (C.s. Rosea). The New Zealand pampas grasses carry their plumes to one side of the stem; toetoe (C.fulvida) is another big grass, with golden-brown flowers which persist well into winter, but it is not for the coldest areas, and needs protection in its first winter. C. richardii, another big New Zealand pampas grass with creamy flower panicles, is salt-tolerant, so particularly suitable for coastal gardens. Cortaderias need full sun and moisture-retentive, well-drained soil; the leaves have very sharp edges, so don’t grow them if you have small children and wear gloves when cutting out damaged leaves.
Some of the larger silver grasses (Miscanthus sinensis) can also make good specimens, particularly the 2m tall M.s. Malepartus with its slender, arching leaves with a white midrib and reddish, feathery flower-heads from late August. The majestic M.s. Silberfeder (Silver Feather) AGM grows as tall as 7’/2m and is always the first miscanthus into flower; the silvery plumes last well into winter. Miscanthus is deciduous; it needs fertile, well-drained soil, preferably moist, and most need full sun; cut back to the base in late winter to let the new growth come through.
Another good specimen grass is the cool-season golden oat grass, Stipa gigantea, with long-lasting, golden, oat-like flowers from midsummer on long, arching stems to 8’/2.5cm above a much lower mound of evergreen leaves. It is particularly good on a corner where two beds meet, as you can see through the flower-stems and flowers to the planting beyond. It’s beautiful when back-lit by the sun. Grow in full sun and fertile, well-drained soil; despite the delicacy of the flowers, this grass tolerates coastal exposure.
Grasses grown in groups
Some grasses are very effective grown en masse, if you have the space, like the very adaptable, evergreen pheasant grass (Anamanthele lessoniana), with its narrow, orange-streaked, olive-green leaves and airy, crimson flowers in midsummer. It will grow in full sun or partial shade in any well-drained soil, and tolerates drought and exposure; avoid a gravelled area, as it’s a copious self-seeder.
For a more architectural effect or in a formal courtyard, try grid-planting the wonderfully upright feather reed-grass Calamagrostis x acutiflora Karl Foester AGM, whose narrow, bronze flowers emphasise its 5’/1.5m verticality. The shorter, slightly more arching C.x a. Overdam is variegated, with vertical cream stripes and airier, purplish flowers, which appear quite early; it is also a good plant for borders. Calamagrostis likes well-drained soils, in full sun or partial shade.
This way of growing grasses is a drawn from the tall-grass prairies of mid-west America, with late-flowering perennials growing among warm-season grasses. On the prairie, self-sown plants formed ever-changing, low-maintenance communities, all liking the same conditions, but moist, cool Irish conditions are a long way from the hot, dry summers, searing winds and freezing winters of the American prairies. Although seed-sown prairie plantings can sometimes survive in northern European gardens, they are often overwhelmed by cool-season plants, and it’s far more common to plant grasses and perennials in drifts.
This is a method popularised by the Dutch designer and nurseryman Piet Oudolf, using prairie plant cultivars bred to cope with the northern European climate, and non-prairie plants which suit the style and conditions. The idea is to choose ‘matrix’ plants, usually tall grasses planted in large numbers to anchor the planting, and then perennials, all planted in drifts. This is not all that different from planting an herbaceous border (with the maintenance that implies) although the planting will evolve somewhat over the years. The big difference from border planting is that it’s best in the open, not backed by a wall or fence, so that the grass-heads can be back-lit by morning, noon and evening light – the different effects are fascinating and enchanting.
Tall, warm-season grasses like silver grasses and calamagrostis work well for the matrix, along with big drifts of sturdy, colourful perennials like heleniums, taller rudbeckias, phlox, asters, golden rod, bergamot, tall achilleas and small-flowered sunflowers like Lemon Queen. Choose perennials with different shapes, colours and flowering times, and include species plants as well as cultivars, for a naturalistic and interesting look. Finally, add a few random tall plants that set off the others and give a more naturalistic feel.
You can include plants that were reared a long way from a prairie – what is important is that all your plants like the same conditions – full sun and well-drained soil being the most important – and can be cut back at the same time. This can leave the bed rather bare in the early part of the year, so many people plant early bulbs and a few low, early-flowering perennials among them.
This style of planting is best in a large bed, but It’s perfectly possible to plant up quite a small bed, preferably an island bed, as long you can squeeze in five at least of each perennial, and more drifts of grasses.
Grasses also have their place in a border. Grasses with a strong architectural quality are good as structural elements planted at regular intervals along the border. Silver grasses (Miscanthus sinensis) are particularly good, including the excellent and reliable M.s. Ferner Osten (Far East) AGM, with slender green leaves with a white midrib which turn coppery in autumn, and gorgeous, deep-red plumes from mid-August, which gradually fade to silver. Another real beauty is my own favourite, M.s. Morning Light AGM, a smaller, wonderfully graceful fountain of slender, arching, pale green leaves with narrow ivory edges which never grows stout and shapeless. M.s. Morning Light will only produce its pink, plumy flowers after a really hot summer, and it flowers late, but its supreme elegance earns it a place in any border; it is also, unlike most silver grasses, tolerant of light shade.
Korean feather reed-grass (Calamagrostis brachytricha) is also good in borders, with arching, grey-green leaves turning golden-yellow in autumn and fluffy purplish flowers, which persist well into winter, and are especially lovely when frosted. Pheasant grass (Anamanthele lessoniana) gives a looser, evergreen structure, but beware of its tendency to spread by seed and grow stocky.
Molinia grasses like Transparent can be planted in the middle of a border, with the lovely slender stems allowing views to the plants behind, in the same way as ‘transparent’ perennials like Verbena bonariensis (purple top) or giant scabious.
Taller grasses in borders look well with herbaceous perennials with fairly substantial leaves and with richly-coloured, clearly-shaped flowers, especially ones like those of Allium sphaerocephalon, tall sanguisorbas like Red Thunder, or hardy geraniums, which rise above their clump of leaves as bright, rich dots of colour against the mobile, linear grasses.
Pony-tail grass, Stipa tenuissima, and its even lusher cultivar Pony Tails, is a smaller perennial grass for near the front of the border; jade green at first, it fades to blonde, and seeds about mildly. It’s stunning with clipped box, and with smaller perennials like Achillea Walther Funke, Geum Queen of Orange and Sanguisorba Tanna.
Grasses come in varied and beautiful colours and in variegated forms. Some of the most attractive grasses are steely-blue, and because they draw the eye, they can be used as focal points in a border. Elymus magellanicus forms a dense clump of metallic blue leaves, up to 3’/90cm, which remain evergreen in mild areas, and has taller stems of blue flowers in early summer. Cool-season, drought-tolerant Festuca glauca is equally blue, but much smaller at 1’/30cm, and with pretty blue flowers.
Carex buchananii, the leatherleaf sedge, has slender bronze leaves, and its cultivar Red Rooster is copper-red. Carex testacea, the orange New Zealand sedge, is an attractive orangey-brown in full sun, and the little red hook sedge, Uncinia rubra, is a mahogany red. Like all sedges, they like a reliably moist soil.
Tough, deciduous Hakonechloa macra Aureola AGM, the golden hakonechloa, makes a low but imposing tussock of arching yellow leaves striped green, taking on reddish tints in autumn; a real eye-catcher, it likes moist, humus-rich soil and full sun or partial shade.
If you have a shady border, Bowles’ golden grass, Milium effusum Aureum, is 2’/60cm, has gorgeous bright yellow foliage in spring, and looks wonderful with blue spring bulbs and against the unfolding croziers of ferns. Short stems of green flowers appear in early summer.
Growing grasses in containers
Because they have such a long season of interest, grasses are very useful in containers, livening up a balcony, patio or courtyard. Any of the small colourful sedges or Festuca glauca can be planted in identical pots for a formal effect in a small space, or be used to contrast with or complement a group of potted perennials or small shrubs. Taller grasses with an architectural quality can be grown in large pots as single specimens, or in pairs, either side of steps, say.
For a tiny courtyard pool, try the golden-variegated slender sweet flag, Acorus gramineus Ogon, a slow-growing, 1’/30cm grass-like perennial with slender, yellow leaves vertically striped with greenish-yellow; it will grow in 2”/5cm of water, as a very attractive marginal plant, or in reliably damp soil.
Go to the Future Forests website for more information about these grasses and grass-like plants, and more.
- Maria Collard