When I was studying horticulture in the late 1990s, received wisdom dictated that you should group blocks of three or more of the same plant, thereby achieving a patchwork of colours and textures. These conventionally planted borders looked a bit static and old-fashioned to my eye, so I began to experiment by adding a few of the neighbouring plants to the edges of the blocks to break them up, and bringing in some of the newly popular grasses to maximise the sense of movement.

I didn’t know it at the time, but I was using what has since become known as tapestry or mixed-matrix planting. In the past two or three years, the technique has become so popular that at the RHS Chelsea Flower Show and the other big shows – always reliable barometers of what is in vogue – few show gardens have been without an area of mixed-matrix perennial planting.

It is impossible to pinpoint the origin of this fashion. In that curious way in which a trend seems to sweep across the creative community, many of the world’s garden designers – including some of our own – have simultaneously moved in the same direction.

Inspiration came, in part, from prairie planting, which takes its influence from the natural planting of the plains of North America. The colours of that style are often subtle and subdued – and, as the name suggests, it is better suited to wide expanses of land than a back garden in Birmingham. Mixed-matrix planting, in contrast, can be used successfully on a small scale, and the method lends itself to both urban and rural settings.

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The key to getting the look right is to bring in softer plants to fill the gaps between more solid individual perennials. Grasses are particularly useful; the thread-like Stipa tenuissima instantly melds things together and stops the scheme looking bitty. Stipa gigantea, favoured by the designers, adds softness, movement and transparent height. This wonderful grass was the star performer when Tom Stuart-Smith wowed the crowds at Chelsea last year with his seemingly effortless but exquisitely planted beds.

This is what it’s all about: the appearance of informality, movement and natural planting. Beneath this apparent insouciance, however, is a carefully conceived planting scheme. Attention to detail, with the plants closely positioned to avoid gaps and hide bare soil, will ensure that they combine to make a satisfying whole, rather than a sporadic mishmash.

Grasses may be obvious contenders, but other plants can fulfil the same adhesive role. Bronze fennel is particularly useful, not only for its russet-coloured stems, billowing airy foliage and delicate flowerheads, but because it is tall and weaves its magic amid other stately perennials. Another good softener is the cloud-like Crambe cordifolia, which forms a frothy haze of tiny white flowers, but looks best when the rather messy foliage on the lower parts of the stems is hidden by neighbouring planting.

Also important is the shape of the perennials that these glue together, and the size of their flowers. Strong, slender vertical stems are invaluable: clumps of upwardly mobile salvias and some of the daintier varieties of verbascum spear their way through the adhesive plants that surround them. Other suitable perennials, such as scabious, san-guisorba, geum and knautia, have small, button-like flowers on skinny stems that will dart among the neighbouring grasses.

Another useful contrasting shape is provided by horizontal flowerheads amid these verticals and dreamy grasses. Achilleas may be short-lived, but they are well worth adding for their flattened heads of tiny flowers in offbeat colours.

Whether you opt for the subtlety of tone on tone or the vitality of clashing brights, colour is crucial to successful mixed-matrix planting. I have seen wonderful examples involving only the softest pastels; pale dusky pinks work beautifully with the shimmer of airy molinias and silken Stipa tenuissima. But some of the most memorable schemes have used intense colour combinations – often including imperial purple with orange, lime or gold – that develop into a rich haze of shimmering brilliance with the addition of bronze fennel and ruby-tinted grasses.

Because mixed-matrix planting relies on mid- to late-season perennials and grasses, it can be difficult to sustain year-round. The best solution is to underplant with spring-flowering bulbs – in particular tulips. Leave the grasses to catch the haw frost through the winter and cut them back just as the bulbs emerge. To stop the dying leaves of the tulips spoiling the effect, as the fresh new perennial and grass foliage breaks ground, I prefer to lift them after flowering and put in new ones each autumn.

Bear in mind, when spacing the plants initially, that they will all bulk up. Leave room for grasses to grow and fill the space with more perennials to begin with, moving them elsewhere when the grasses have filled out. Once the planting is fully established, you will find that it needs refreshing and reorganising every few years.

RECOMMENDED PLANTS

Foeniculum ‘Purpureum’: best suited to full sun, bronze fennel has airy, plume-like foliage and attractive dull-yellow flowers that are followed by distinctively aromatic seeds.

Geum ‘Dolly North’: glowing orange flowers on slender stems are produced throughout the summer over a clump of basal leaves.

Imperata cylindrical ‘Rubra’: this flame-like grass forms well-behaved, upright clumps of leaves that are initially green, then turn scarlet and crimson.

Knautia macedonica: one of my must-have perennials, blessed with small burgundy flowers that last for ages on the tips of the skinny stems.

Salvia x sylvestris ‘Main-acht’: slender spikes of rich indigo-purple, a colour of such intensity, it glows.

Sanguisorba ‘Tanna’: at only 16in, this low-growing form makes neat mounds of foliage, the thin stems topped with bobble-shaped flowers in deep crimson.

Scabiosa atropurpurea ‘Chile Black’: a wonderful form, with maroon flowers. Stipa gigantea: ideal for mixed-matrix planting on a grand scale, the golden oat produces 6ft flowering spikes above the basal clump of leaves, but is so transparent that low-growing plants are veiled rather than obscured.

Stipa tenuissima: a justly popular, tactile grass. At about 20in in height, the silky fronds are not too tall, allowing the flowers of most suitable perennials to shine through.

Verbascum ‘June Johnson’: good for providing a strong vertical accent. The mauve-flushed apricot flowers work well with bronze carex or fennel.

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