Which ornamental grasses are right for my garden?

Ornamental grasses, why are they the swaying stars of the autumn border

Every season brings its own garden wonders and, apart from the awe-inspiring colour of leaves, ornamental grasses are the stars of early autumn. Grass seed heads and flower heads look beautiful for months. They are more durable than most flowers and certainly delight the senses for a longer period of time than the beautiful show of autumn foliage. But did you realise that there are several different categories of ornamental grasses? Each grows into a form that is distinctly different from others. Some are more suitable for gardens than others, especially small spaces.

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Clump-forming types

Many Miscanthus grasses are cespitose in habit, forming into mounds that come from a central point, as in the photo above. They don't generally spread outwards too far as they don't use 'runners' for reproduction. These cespitose grasses are probably the most common of the ornamental grasses, and some of the most loved, of all types. They have a mounded habit, bunching out from a central base. The grasses form a pleasing, tight tussock which doesn't tend to spread beyond where you've put it, once it has matured into its ultimate size. These are a gardener's friend because you can rely on them not to take over your garden they stay roughly where they are put. without spreading to different locations.

Some of them have viable seed, however, and new plants can therefore spring up around and about quite easily. ‍Anemanthele lessoniana (above), also known as pheasant's tail grass, is a superb cespitose tyle ornamental grass that stays in a pleasing clump. But it does spread by seed.

Long-lived tussocks

Examples of cespitose grasses include Deschampsia cespitosa, a grass with golden stems and fine seedheads, being native to Britain. Also the tussock-forming Molinia caerulea; the immensely popular Stipa gigantea and sedge grasses such as some Carex and Festuca. Many of these cespitose ornamental grasses are long-lived and over time they can form large tussocks. Some are evergreen, thereby providing structure and form all year round.

Matt-forming grasses

Then there are mat-forming ornamental grasses, a term that doesn't really do justice to some versatile wonders of the autumn border. Calamagrostis Karl Foerster, for example, is a popular vertical grass that gradually spreads into ever-increasing clumps. It grows deliciously, but slowly, bigger with each passing season. ‍ It has upright, straw-coloured stems and seedheads that look great as a vertical accent in a garden and this grass can withstand just about any amount of wind too. It's also good in coastal gardens. 

There's a very good reason why certain cultivars are developed, as one of this Calamagrostis parents (C. epigejos) spreads so vigorously that it can quickly take over an entire garden. Phalaris, for example, are vigorous, spreading grasses, some of which love damp places. They can easily swamp you if they are not kept in check. ‍

The plumes of pampas grasses and other clump-forming ornamentals looks beautiful against the right background. They need space to spread but won't travel too far.

Useful as groundcover

Grass-like plants such as Liriope species and Ophiopogon, can be treated very much as groundcover as they will creep and reproduce, almost without you noticing.  Bulrushes and common reed are excellent examples of grasses that aren't always welcomed in a garden environment due to their spreading nature. ‍Bulrushes, or Typha species, can be vigorous and spreading and can soon take over a pond.

Turf grasses that spread

Turf grasses need little explanation. They run using stolons, and they seed too. They can be mown and don't generally form into mounds. Turf grasses are utility species which are ideal for lawns, sports pitches and for grazing by animals. We grow them for their useful carpeting habit and their fresh colour rather than their seedheads and beautiful habits. ‍

Bamboo

But in the same scientific family of Poaceae are bamboos, of which there are around 1000 species. Some of these are giants and many are thugs of the plant world, spreading vigorously using a running habit. But others are sedate, clump-forming beauties that are well-worth fitting into a garden, if you have the space. These include Fargesia and Bambusa, some of which grow to only two metres high. ‍The Fargesia in the photo is being used as a hedge and is clipped, but generally this type of bamboo is well-behaved.

The largest bamboo in the world

Dendrocalamus giganteus is just about the largest bamboo species you will ever find, and this is not generally available here in the UK because it isn't hardy in our climate. It is also called giant or dragon bamboo, because it can grow to a height of up to 35m! The diameter of the stems is up to 30cm and it has a dense, clumping habit. Native to China, Thailand and Myanmar, this is a naturally occurring plant but also grown as a crop. It can be used for scaffolding, boat masts, rural housing, water pipes and furniture.

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Some are great in pots.

Here in the UK, there's a bamboo for just about any garden and even a courtyard. Why? Because this is a plant that will tolerate being in a pot provided you feed and water it regularly. It offers great screening potential and is supremely eye-catching, particularly when the stems are cleared of shoots in order to achieve vertical impact. Choose the appropriate plant for the space, and don't be too afraid of its height. It's the spreading that can pose a problem, so pick a clump-forming variety instead.

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Bamboo has the most amazing stems which can add vertical drama when cleared of shoots. Even in a small place, a large specimen looks impressive. Give it some space around the stems to enable you to gain the full, structural benefit of its appearance. This is a sculptural plant which can add instant impact. Two good ones for this purpose are Phyllostachys aurea and Phyllostachys nigra. Enjoy!