Why the traditional border still works

There is a reason the long herbaceous border has survived every shift in garden fashion. A well-made border gives you more than flowers: it gives you a season. It opens with bulbs, swells through early summer, reaches its crescendo in high summer, then settles into seedheads and grasses that carry the garden through to the first hard frost. In a country house setting, where the border often runs along a wall, a yew hedge or a gravel path, it also does something architects have always understood: it holds the space, giving the eye a rhythm of verticals, mounds and spires.

The traditional approach relies on hardy perennials, supplemented by bulbs and ornamental grasses. That trio is the whole trick. Perennials supply the bulk and the colour, bulbs fill the gaps before the perennials wake up, and grasses knit everything together while extending the performance into autumn and winter.

Getting the ground right

Herbaceous perennials are asked to live in the same spot for years, sometimes decades, so the preparation you do now is the best investment in the border. A border two metres deep and six or seven metres long is a sensible starting size; deeper than three metres and maintenance becomes awkward from one side.

Before planting, clear perennial weeds thoroughly. Ground elder, bindweed and couch grass will not politely stay at the edges, and digging them out after planting is miserable work. Then improve the soil to a spade's depth and beyond:

• On heavy clay, dig in well-rotted manure or garden compost and add grit to improve drainage.
• On light, sandy soil, add plenty of organic matter to hold moisture through summer.
• Aim for a soil that is moist but free-draining, with a pH around neutral; most perennials are tolerant, but they sulk in waterlogged ground.
• If you garden on chalk, work in compost and choose plants that enjoy lime, such as Nepeta, Salvia and Scabiosa.

Leave the ground to settle for a fortnight before planting, and take the opportunity to set out your paths. A mown grass path or a strip of gravel beside the border saves endless trampling of the soil behind the front row.

Designing the planting plan

The classic border is arranged by height, with low plants at the front and tall ones at the back. That works perfectly against a wall or hedge. Where the border is viewed from both sides, put the tallest planting down the centre and graduate downwards to each edge.

Colour is where the character of your border is decided. Two approaches have stood the test of time:

• Harmonious planting, using soft blues, pinks, mauves and silvers, which suits a period property beautifully and always looks calm.
• Contrasting planting, hot oranges and reds against deep purples and bronzes, which gives a border real presence in high summer.

Whatever you choose, plant in drifts rather than single specimens. Groups of three, five or seven of one cultivar read as a sweep of colour rather than a jumble. Repeat the same plant two or three times along the border to pull it together, and include a few plants with strong foliage, such as Alchemilla mollis or a purple-leaved Physocarpus, to rest the eye.

Build in season. Aim for something in flower every month from April to October: Pulmonaria and Doronicum in spring, Peony, Iris and Delphinium in early summer, then Phlox, Helenium, Crocosmia, Verbena and Persicaria into autumn. Finish with Sedum, Aster and late Penstemon, which flower until the frosts.

Bulbs and grasses: the quiet scaffolding

Bulbs are what separate a good border from a great one, because they fill the gap before perennials have made any size. Plant alliums among your perennials for late-spring globes on bare stems, tulips for May colour, and small bulbs such as crocus, snowdrops and Anemone blanda in the front few centimetres. Let the foliage of later bulbs die back naturally; the surrounding perennials will hide it as they grow.

Grasses do the same job at the other end of the year. A clump of Miscanthus, Deschampsia or Stipa adds movement on a still day and structure when everything else has collapsed. They also look superb left standing through winter, catching frost and low sunlight.

Planting, spacing and staking

Plant in autumn or early spring, when the soil is warm and moist. Space most perennials 30 to 45 centimetres apart; they will close the gaps within two seasons and you will get better, sturdier plants than if you crowd them. Water them in well, even if rain is forecast, and mulch the whole border with two to three centimetres of well-rotted compost, keeping it clear of the crowns.

Staking is the difference between a border that looks deliberate and one that flops after a summer storm. Set supports in April or early May, before plants are tall enough to need them. Hazel peasticks suit a period property perfectly, and a grid of twiggy stems hidden in the foliage will hold even a heavy Delphinium upright without looking like scaffolding.

A year of maintenance

Herbaceous borders are not low-maintenance, but the work is seasonal and satisfying:

• Spring: cut back old growth, fork gently around crowns, feed with a balanced fertiliser and mulch. Watch for slugs on new shoots.
• Late May to early June: the "Chelsea chop" on later-flowering perennials such as Sedum, Aster and Phlox shortens plants, delays flowering slightly and reduces the need for staking.
• Summer: deadhead to prolong flowering, water deeply in dry spells, and hoe the edges of the border.
• Autumn: divide overcrowded clumps every three to five years, and plant new bulbs.
• Winter: leave seedheads and grasses standing for wildlife and structure, then cut back in late February or March.

Keep the soil fed and the weeds down, and a traditional border will go on improving for years. Few things suit an old house better than a long sweep of perennials, and few things repay patient planting more generously.