Why you should plant ornamental grasses this season

Piet Oudolf’s style of perennial planting as seen in Berne Park Bottrop, Germany
Piet Oudolf’s style of perennial planting as seen in Berne Park Bottrop, Germany - Alamy

Ornamental grasses are so useful, in so many ways. They can be threaded through a border to unify a planting scheme: the classic example of this is Dutch garden designer Piet Oudolf’s use of Calamagrostis x acutiflora ‘Karl ­Foerster’. He snakes this metre-high, ramrod-straight “rocket” of a grass through late-season perennials to ­create an enduring backbone that persists into winter. At the other end of the scale, the Japanese Hakon grass Hakonechloa macra curtsies lower than any other. This deciduous, long-lived grass comes in gold and green variations and it’s very good in simply planted containers. Other grasses produce veils of tiny, lacquered beads, and some, such as the South American Pampas grass, Cortaderia selloana, act as strict punctuation marks: proceed no further!

The imposing South American Pampas grass
The imposing South American Pampas grass - Alamy

The difficulty is choosing the right grass for you, because many are at the northern limit of their range when planted here. Your location will affect flowering times: for example, my varieties of Miscanthus sinensis creep into flower in September, a full six weeks later than those in the banana belt of southern England. Some grasses fail to flower at all in the cold Cotswolds where I live. It’s a step too far for ­panicums, for instance. I’ve learnt not to bother. Neil Lucas of Knoll Gardens is an expert on grasses and his new book, Grasses for Gardens and Landscapes, reflects years of knowledge garnered in this country. Knoll ­Gardens supplies a wide range of well-grown plants; the garden opens widely and you can book in for masterclasses.

All of the grasses suggested below (apart from the seed-raised ones) can be planted in the garden now. If you’re on heavy clay, add some coarse grit to the base of the planting hole.

Spring sensations

The most useful early-season grasses have a low, evergreen presence because the garden is mainly full of ground-hugging plants at that time. The golden foliage of Luzula sylvatica ‘Aurea’, the greater wood rush, ­provides a splash of sunlight and I love to see it pushing through dark leaf ­litter, under deciduous hazels or viburnums. The taller Luzula nivea, aptly named the snowy wood rush, produces slender stems topped with clusters of apple-white flowers. These are rushes, honorary grasses.

The lime-yellow foliage of the golden wood millet, Milium effusum ‘Aureum’, lights up the ground over the winter months and that’s unusual. Most golden-leafed plants turn green when temperatures fall. As May approaches, airy wands of shiny yellow beads gleam in late-spring sunshine, persisting into summer. This dainty grass does self-seed, but it’s easily spotted and removed. A little later, the 30cm-high wood melic, Melica uniflora f. albida, produces heads of white rice-like beads and it’s the perfect partner for hardy ferns. This creeps, but not aggressively so, and it will self-seed too. Find a quiet corner for this delicate beauty.

Some grasses seem tailor-made for pots and containers. The fine-tuned Carex testacea, known as orange sedge, is another honorary grass. It swirls and arches downwards from a tight waist. The colour changes throughout the year, from ginger to cola, as long as it’s in a bright spot. I love this rugged New Zealander when it’s underplanted with blue Anemone blanda.

Cortdaeria richardii and Cotinus coggygria ‘Royal Purple’ in Val Bourne’s garden
Cortdaeria richardii and Cotinus coggygria ‘Royal Purple’ in Val Bourne’s garden -

Summer magic

Summer grasses create a golden haze in sunlight and Stipa gigantea, or the giant oat grass, is the most indispensable early-summer performer. It needs full sun, or a very bright position, along with a spacious spot because the fine glaucous foliage forms a substantial mass. It survives wet winters far better than many other stipas and it doesn’t mind being trimmed round the outer edges in winter. This prevents it from smothering its neighbours. Tall stems splay outwards, like a series of giant golden sparklers. The heads oversee May’s purple alliums and carry on until late autumn, becoming more etiolated as the days cool off and shorten. I saw it mass-planted in a serpentine border at St Hilda’s College in Oxford, jostling among an equally tall pink mallow named Althea armeniaca, along with purple Verbena bonariensis and Verbena rigida. Stunning!

Stipa gigantea is an early-summer performer
Stipa gigantea is an early-summer performer - Alamy

I am a great fan of Stipa barbata, a feather grass with slender ostrich-like silken plumes in midsummer. It’s the garden version of Rapunzel, although the dart-pointed seeds detach themselves by late summer. However, this temperamental short-lived grass needs good drainage and a warm site, so it can be hit and miss. Wet winters sometimes see it off, so I’ve been unfaithful. I’ve planted an easier feather grass from Peru, named Stipa ichu, also sold under Jarava ichu. I saw this metre-high grass flouncing through Roger and Jenny Lloyd’s plant-packed NGS garden named Highfield Farm near Pontypool, an area of Wales with plenty of rainfall. This garden also opens for groups; check out the NGS website.

Movement is an added bonus when it comes to ornamental grasses and the tempo can change from a slow waltz to a quick foxtrot, according to the weather. The New Zealand Toetoe grass, Cortaderia richardii, rises to three metres or more and, on windy days, it resembles an agitated Simon Rattle in full flow. It produces tall stems by early July, topped by flowing beige flowerheads. That’s 12 weeks before its South American cousin, Cortaderia ­selloana, begins to produce rigid, upright plumes. But toetoe needs a large garden. Mine began to threaten the nearby stone wall, so it went. I miss the mad ­conductor. My hedgehogs used to hibernate in it too.

Stipa ichu, also sold under Jarava ichu: a feather grass from Peru
Stipa ichu, also sold under Jarava ichu: a feather grass from Peru - Alamy

Seed-raised grasses are easily grown and they add a gossamer touch in sunnier positions. Although many are really short-lived perennials, I treat them as annuals and sow in April, because they fail to overwinter. Quaking grass describes Briza media perfectly, because the tiny pale-green spikelets dance in the breeze. There’s a new, compact one named ‘Golden Bee’ that’s on my ever-expanding shopping list. I always find room for Hordeum jubatum, the bristly crook-necked foxtail barley, and Pennisetum macrourum. The latter produces long, slender buff-white “tails” by late summer. It’s fairly perennial here.

Perennial pennisetums form fluffier bottlebrushes in shades of coffee, cream, burgundy and smoke-black. Their bristles are adept at catching September dew drops, but if you’re above the Watford Gap they will perform in autumn rather than in summer. The hardiest stalwart, for cooler climes, is Pennisetum alopecuroides ‘Hameln’. I admired the browner ‘Cassian’s Choice’, used by Charlotte Harris and Hugo Bugg at September 2021’s autumnal Chelsea Flower Show. It hasn’t performed in this sunless ­summer, so the jury’s still out.

Year-round grasses for your garden
Year-round grasses for your garden

The late-late show

Taller grasses come to the fore once the days shorten and there’s plenty of choice. Taller molinias, or purple moor grasses, have arundinacea (meaning reed-like) in their Latin name. They produce their flowerheads by late summer, but need cutting back by Christmas at the latest, because the stems crash. They’re a variable lot visually. The airy ‘Transparent’ is very see-through, as the name suggests. ‘Karl Foerster’ turns a rich yellow as temperatures fade. The ever-trembling ‘Windspiel’ and the upright ‘Skyracer’ also colour up in autumn. Variable seedlings will occur.

It is miscanthus season and they’re just as variable as molinias. The fresh plumes can be reddish purple and ‘Ferner Osten’ and ‘Malepartus’ are both superb examples. Excellent silvers include ‘Silberfeder’, the most reliable flowerer in cooler gardens. They all fade to buff brown or white in time. Good and very available forms, suited to smaller gardens, include ‘Kleine Silberspinne’ and ‘Starlight’.

However, it’s not all about feathery awns: some miscanthus have wonderful foliage too. Gertrude Jekyll (1843-1932) cast light and shade in her Munstead Wood garden with the horizontal yellow stripes of ‘Zebrinus’, a much more graceful plant than the similar ‘Strictus’. The finely variegated green and white ‘Morning Light’ forms a fine, cool column, but only flowers after a hot summer. In any case, they’re a distraction. Like a teenager trying to grow a beard. If you want brash, the broader green-­centred and white-edged leaves of ‘Cosmopolitan’, or the slightly less out-there ‘Cabaret’, both provide bold ­foliage with a touch of the exotic.