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Gardening with Grasses

Read a fascinating and in depth article written by Becky Martin, the Nursery gardener, on how gardening with grasses can create maximum impact.

Grasses were probably among the first plants to be cultivated by ancient man when he started to grow cereals for food. These species have been developed into our modern cereal crops which feed the world. Ornamentally, grasses come and go as fashion changes, but they are currently mainstream in garden design. They feature heavily in prairie planting schemes, modern minimalist gardens, as well as designs with native plants and for wildlife.

In gardening, the term “grasses” is used loosely to include many plants which, botanically, are not grasses. There are over ten thousand species of grass, and over 3 thousand species of sedge. Restios, rushes and sedges are not grasses, though bamboos are. Apart from their linear foliage, plants like Ophiopogon and Phormium bear no relation to grasses, but are often on sale in the “grasses” section. For gardeners, as long as a plant’s individual cultural requirements are met, the taxonomy can take second place.

It is however, helpful to understand a bit about the way grasses work. They fall into two categories: warm temperature grasses and cool temperature grasses. The distinction is made on the way they grow and metabolise, or photosynthesise. Warm temperature grasses grow fast from spring to autumn but are most efficient at high temperatures. They open their pores at night to take in carbon dioxide, thus reducing the risk of moisture loss. In our climate these are late to start into growth, grow slowly until the weather warms up and then grow steadily gathering speed for flowering at the end of summer. Growth stops with the onset of cold weather, but this brings good colour changes in the foliage. They remain dormant all winter. Arundo , Cortaderia, Eragrostis, Imperata, Miscanthus, Molinia, Panicum and Pennisetum all fall into this group. Cool temperature grasses make optimum growth in cooler moister conditions, like our spring and autumn. These grasses tend to stop growing if the weather is too hot and dry. Lawns are a perfect example. They tend to flower in early summer and may remain evergreen, or semi-evergreen. This group includes most lawn and cereal species and also Carex, Luzula, Milium, Festuca, Poa and Stipa.

The growing season matters because grasses dislike disturbance when they are dormant. The warm temperature grasses will have exhausted themselves at the end of the summer, especially if they have flowered, and may not recover from being moved or divided in the autumn. The best time to meddle with all grasses is therefore in spring or early summer when they are in active growth.

There are two ways of using grasses in the garden. First is as a flat surface (much as you would use carpet as floor covering in a house) and is generally a lawn. The second is when plant is selected for the individual qualities it will contribute to your planting scheme, chosen in much the same way as a shrub or perennial, and planted singly or in groups. Grasses are versatile and widely varied, there will be a grass for every conceivable garden situation. They provide texture, are invaluable for wildlife, both as a food source and for shelter. They provide a safe winter haven for overwintering insects. They change subtly over the seasons. They can provide a substantial screen or an attractive border edge. They catch the light beautifully, particularly when the sun is low early or late in the day, though early morning adds dew to the picture. Above all they are easy to look after.

Deciduous grasses will have become straw or biscuit coloured over the winter, and show no green. These will need to be chopped back hard to allow the new shoots to emerge. That really is all you need to do, once a year. If you fail to do this, the new growth will come through the still-standing dead growth and look unattractive, and be very fiddly and time-consuming to sort out. The grass can be cut right down to ground level, taking care not to damage any visible new shoots. If you have a rabbit problem, leaving about 20cm of the dead growth seems to lessen the damage. This is best done at the end of winter before growth starts. A word of warning here; don’t be enticed by wonderful pictures of hoar frost crystals, and sparkling ice on your winter grasses. In Cornwall such frosts are rare and unreliable

Evergreen grasses require different treatment, and the regime here is less clear cut. Young plants will need only a tidy up by hand-pulling the scruffy or dead parts out. If the plant does not look better, or it is an older plant, you can cut it hard back, but this must only be done when you can see it is growing strongly. Some evergreen or semi-evergreen grasses will not regain their fresh young looks, and are better replaced after a few years. Many will have self-seeded by then; Anemanthele lessoniana and Carex ‘Frosted Curls’ are good examples of this.

In general, grasses need little or no feeding. Too much nitrogen will result in soft, lush green growth of a uniform colour, and more likely to flop over. Lawns and silage fields are a perfect demonstration. The plants are stronger and colours more pronounced without generous feeding, or on poor soil.

Often a few grasses are mixed in with other plants in a planting scheme where they add texture and contrast. On the other hand, they may be the predominant plants in a scheme, in which case it is desirable to add some other plants for contrast. But what? The plants that fit the bill here are those without too much leaf higher up, those with strong flower shapes, or flowers that appear to float above the grasses. Phlomis russeliana is an excellent contender. Its evergreen leaves obscure the bottom of the grass but its candelabra seedheads add a bold structural pompom effect all winter. Sedums perform similarly. For added contrast at higher levels, Verbena bonariensis is useful, as are Gaura and Persicaria orientalis.

The treatment of spaces between grasses deserves a mention. It is quite fashionable to mulch the area between your grasses with gravel or slate chippings. This looks smart to begin with, but is hard to keep that way. As winter approaches the deciduous grasses lose their colour and tend to shed some debris. The easiest thing is to leave the dead material in situ, but some gardeners may not like this approach and prefer to rake it up as it falls. If you have a coarse mulch, it will be hard to rake up the debris. Inevitably, your grasses will shed some seed, and whilst some species are easy to identify at very early stages, many are not, and you may end up with a freshly sown “lawn” between your clumps of big grasses. The only way to deal with this is to hoe it, but this also will be difficult in all but the finest mulch or gravel.

My personal favourites which have all grow well for me here in Cornwall are as follows:

Cortaderia richardii – a pampas grass from New Zealand which has a tidy evergreen mound of foliage and graceful arching flower plumes. More elegant than Cortaderia.

Pennisetum macrourum – a medium sized chunky grass with wonderful six inch long fuzzy flower heads. Will run but not problematically.

Miscanthus sinensis ‘Cosmopolitan’ - a strong growing variegated Miscanthus with broad leaves. Makes a reliable and fast back-of-border plant. Good backdrop.

Miscanthus sinensis ‘Morning Light’ - a strong growing finely variegated grass with a slightly arching vertical effect. Tidy and easy.

Molinia arundinacea ‘Skyracer’ a tall grass with elegant wiry arching see-through flower stems

Luzula nivea - a native perennial woodland evergreen which grows in shade and has little white flowers which appear to float

Milium effusum ‘Aureum’ - an annual for shade with bright yellow-green leaves. The seeds appear like tiny gold beads hanging from an arching stem. Self seeds gently.

Anemanthele lessoniana (formerly Stipa arundinacea) - a really useful evergreen grass which has wonderful red-bronze autumn colour, but will grow well in shade and remain green. Moves well in the wind. Self seeds.

Hordeum jubatum – wild barley. Short-lived but self seeds. Attractive textured grass, dries well.

Lagurus ovatus – Bunny Tails. Irresistibly tactile white flower heads.

Stipa tenuissima – a delicate fine grass, invaluable for adding texture and movement. Catches the light wonderfully.

Carex comans ‘Frosted Curls’ – pale grey-green blades curling back on themselves. Easy and useful at border front.

And finally, two books I would recommend are The Encyclopedia of Grasses for Livable Landscapes by Rick Darke which is a lavishly illustrated and beautifully written book about grasses all over the world. For a more practical slant, Designing with Grasses by Neil Lucas (of Knoll Gardens, Dorset) gives excellent advice on growing grasses in the UK, with useful lists of grasses for different situations. Christmas is not that far away!