Designing with Grasses – Knoll Gardens – Ornamental Grasses and Flowering Perennials

Quite apart from providing beauty and colour from flower or leaf shape, much as many other plants will do, grasses offer an additional range of distinctive talents that make them invaluable to the gardener and the designer. These near unique qualities can make a huge difference to our gardens, and are so very easy to use successfully. The key characteristics that follow include some that can be enjoyed for their own sake along with others that make grasses particularly useful for certain purposes or situations.

Morning light show – the massed fluffy flowers of Pennisetum Black Arrow radiating every drop of early sunlight in the Dragon Garden.

Sunlit and Backlit

Very few groups of plants are transformed as dramatically as grasses by the effects of different kinds of light. Grasses that really make the most of the light are the ones whose flowers are held clear above the foliage, allowing them to take full advantage of the reflected sunlight. A favourite in this respect is Miscanthus Memory, whose large flowers are held aloft on tall stems and seem to almost glow in the warm sunlight. But there are also many others from which to choose. The fountain grasses such as Pennisetum Fairy Tails or Pennisetum Dark Desire, with their masses of fluffy caterpillar-like flowers, also excel. Panicum, Deschampsia, Calamagrostis and Molinia are all equally responsive to light. For more ideas and examples take a look at our online Sunlit and Backlit gallery.

Miscanthus Memory has large near white flowers that are simply breathtaking when lit up by sunshine.

Hakonechloa macra, the japanese forest grass, demonstrating just how effective its linear shape and form can be in association with other plants and hard surfaces.

Texture and Shape

There are a number of grasses whose foliage has particular textural value. Take for example the japanese forest grass, Hakonechloa macra and its forms, whose refined, elongated leaves make a perfect foil when set against so many different plants or more solid hard surfaces.

However the textural qualities of most flowering grasses can contribute much to the garden scene. The flowers of most grasses will remain intact for many months after the initial flush of colour has long since faded, so if they have a textural quality or fine shape they will provide interest and pleasure for longer. For example, Miscanthus Flamingo, a first-class garden plant, has the most elegant, delicately pendulous flowers that are coloured a superb deep pink when first open; although this fresh colour soon fades, the shapely qualities of the flower remain and are arguably almost more effective than the first flush of colour.

The textural qualities of the fading flowers of Miscanthus Flamingo are scarcely less effective now than when in full fresh flower.

In the Dry Meadow Poa labillardierei has been used as a matrix grass that is then accented with suitable perennials such as the white flowered Libertia grandiflora.

Matrix and Mass

Grasses that can be used as a base over the entire planting area and from which other plants are seen to emerge are frequently referred to as a matrix grass. Often limited to a single type of grass this approach is becoming increasingly popular as gardeners and designers alike enjoy both the simplicity of effect and the comparatively low level of aftercare required to maintain such plantings. Inspired perhaps by the meadow principle of a generally grassy open space from which other plants emerge. For example at the Hauser and Wirth in Somerset, designed by master designer Piet Oudolf, a base planting of Sesleria Greenlee Hybrid has been used as a matrix from which other seasonal accent plants emerge in turn. With well chosen partners this essentially simple design approach creates a long season of interest and display with comparatively little aftercare.

Sesleria Greenlee Hybrid used very effectively as a base or matrix grass at Hauser and Wirth, Somerset.

Grasses such as the foreground Nassella (Stipa) tenuissima and the background Stipa gigantea can move and sway seductively in even the slightest wind.

Movement and Sound

Whether though graceful movement provoked by a delicate summer’s breeze or when being battered by severe winter gales, the lithe, flexing, almost-continuous motion and rustling sounds of stems, leaves and flowers is a prime attribute of the grass family. Highly evocative of fabulous natural landscapes, such as coastal reed beds on a windy day, the sound and movement of grasses in our designed spaces breathes life into landscapes that can otherwise appear static and stationary. Nassella (Stipa) tenuissima is a quick growing tactile grass that moves in the slightest wind and can bring life and energy into otherwise relatively static landscapes.

Grasses are seldom if ever heavy; their almost constantly moving stems are produced in great profusion, which even at height and when topped with flower, manage to convey an airy lightness almost unequalled in the plant world. Panicum virgatum and its many selections, such as Panicum Merlot, are expert at creating this light and airy mobile effect as they produce quite literally masses of tiny flowers that appear to hang, cloud-like, above the stems and leaves and sway beautifully in even the lightest of breeze.

The cloud like masses of Panicum Merlot flowers, though temporarily stilled in a sharp autumnal frost, are in almost continual motion when encouraged by even the slightest movement of air.

The tall wiry stems of the tall purple moor grass, Molinia arundinacea, can create a wonderfully delicate and transparent effect. This is a well named selection – Molinia Transparent.

Transparency

Their quick-growing nature and lightness of stem equips certain grasses such as the taller molinias and stipas to act as transparent or semi-transparent dividers of garden space. Excellent at providing height without weight in larger plantings—or in small gardens that are often short of space—these plants provide temporary division and something of an air of mystery as the view beyond can still be glimpsed beyond the screen. In this respect the tall purple moor grass, Molinia arundinacea, is a great choice with its quite unique autumn display that sees the foliage, stems and flowerheads slowly turn the most amazing warm butter yellow.

Stipa gigantea, with its tall airy stems, is another good choice because although it can exceed 2 metres (6 feet), it can easily be used in front of much smaller plants at the front or middle areas of a border or larger planting area thanks to the ‘see-through’ nature of its flower stems.

The giant oat grass, Stipa gigantea, produced many tall upright stems early in the season – through which other areas can be glimpsed.

The strong upright habit and early flowering nature of Calamagrostis Karl Foerster makes it an excellent choice for informal screens and division of space.

Screening and Division

The combination of regular outline, flower, movement and longevity allows a number of grasses to be used very successfully as informal screens or hedging. They are just as easy to maintain when used in this manner as they are when used elsewhere in the garden. Effectively self-levelling, the grasses grow to the same height each season without needing to be trimmed during the busy summer period.

A number of grasses can be used in this way and are superb in many situations where an internal division of space might be desirable. Calamagrostis Karl Foerster, Panicum Northwind, Pennisetum Fairy Tails and the rather taller Miscanthus giganteus are all excellent choices. Unlike more permanent screening and commonly seen hedging plants, when used as lightweight ‘hedging’ grasses have few of the drawbacks of more traditional hedges, are long lived, and seldom become too bulky as the stems are renewed from the base each year. Although most grasses when grown together in this way produce a very even outline the effect is generally informal rather in contrast to the strictly formal effect created by tightly clipped woody evergreens such as box and yew. Added to this, the constant movement of stems, flowers and leaves brings the hedge or screen alive. For more ideas and suggestions take a look at our Grasses for Informal Screens and Dividers gallery.

Pennisetum Fairy Tails can make an effective and floriferous mid height informal division of space in sunny open positions.

A repeated use of the same grass, even when used in pots such as with this Hakonechloa macra at Knoll, helps build up a theme and an identity to a planting.

Repetition

Repeated use of a single plant, or several similar ones, is an effective way of giving a garden a theme or recognizable pattern. Repeated plants, in groups or used as individuals, sometimes become known as signature plants because they help give a planting its particular identity. Being quick-growing and amenable to close grouping, and with their distinctive linear outline, grasses are well placed to excel in this role. As repeated individual specimens any grasses that have a distinctive outline such as Miscanthus, Molinia, Panicum, Poa and Calamagrostis are all excellent for this purpose. While those that work well as groups would include Nassella, Deschampsia, Pennisetum and Hakonechloa.