Why perennials are the backbone of a small garden

When every square metre has to work hard, perennials that flower for months on end are worth their weight in gold. Annuals are brilliant, but they need replacing each year, and in a courtyard, balcony or narrow border that repetition of cost and effort soon adds up. Choose the right herbaceous perennials and you plant once, then enjoy colour from early summer right through to the first proper frosts of October or November.

Three groups do this more reliably than almost anything else in British gardens: hardy geraniums, rudbeckia and salvia. Between them they cover sun and part shade, cope with our damp winters, and ask for little more than an annual tidy-up. Get the planting and the mid-season cutting back right, and they will reward you for years.

Hardy geraniums: the reliable front-of-border filler

These are cranesbills, not the tender pelargoniums sold as bedding. They are tough, slug-resistant once established and remarkably long-flowering. The standout for sheer stamina is Geranium 'Rozanne', which starts in June and continues until the foliage is cut down by cold. It mounds to around 40–60cm tall and can spread 90cm across, making it generous but not thuggish.

• Geranium psilostemon — vivid magenta flowers with black centres from June to August. Taller, at about 90cm, so plant it where it can lean on a neighbour or a discreet support.
• Geranium wallichianum 'Buxton's Variety' — soft blue flowers with a white eye, sprawling habit, ideal for softening the edge of a path.
• Geranium x oxonianum — one of the best for dry shade, and it will repeat-flower if cut back after its first flush.

After that first flush, shear the whole plant back to about 10cm with shears. Fresh leaves appear within a fortnight and a second wave of flowers follows. Divide congested clumps every three or four years in spring or early autumn, and water them in well.

Rudbeckia: golden colour for late summer

Rudbeckia carries the border through August and September, just when many early perennials are flagging. Rudbeckia fulgida var. sullivantii 'Goldsturm' is the classic: golden-yellow daisies with a dark central cone, roughly 60cm tall, clump-forming and long-lived in a sunny spot. For containers or the very front of a border, look for shorter forms such as Rudbeckia hirta 'Rustic Dwarfs', which stay around 45cm.

They want full sun and a soil that holds moisture in summer but drains freely in winter — wet crowns in January do more damage than any frost. Protect young shoots from slugs and snails in spring, when the emerging foliage is at its most tempting. Divide every three to five years, and leave the seedheads standing into winter; they look superb frosted and goldfinches will thank you.

Salvia: long-distance flowering with real presence

Salvias bring vertical accents and rich colour, and the hardy herbaceous types are far tougher than their Mediterranean looks suggest. Salvia nemorosa 'Caradonna' produces deep violet spikes from late May into July, then again into September if deadheaded promptly. Salvia x sylvestris 'Mainacht' is similarly reliable and slightly more compact.

• Shrubby types such as Salvia microphylla 'Hot Lips' flower from June to the first frosts, but need a sheltered, sunny spot and sharp drainage.
• Salvia guaranitica 'Blue Enigma' is taller and tender, so mulch the crown thickly in autumn or lift tubers in cold areas.

Drainage is everything. Add grit to heavy clay, plant on a slight mound and mulch with gravel rather than compost to keep the collar dry. Cut herbaceous salvias back to the base after the first flush; for shrubby types, trim the flowered stems but never cut into old, leafless wood.

Pulling the planting together in a tight space

Layer the three groups so something is always in flower. Put hardy geraniums at the front, rudbeckia in the middle and salvia behind for height. Repeating each plant in threes creates rhythm in a small border far more effectively than dotting one of everything about.

Colour-wise, the magenta and violet of geraniums and salvia sits beautifully against rudbeckia's gold. Add a gravel mulch and a few dark-leaved plants for contrast, and the scheme looks deliberate rather than random. In containers, use a minimum 30cm pot, fill with a loam-based compost and group a geranium, a dwarf rudbeckia and a compact salvia for a display that runs from June to October.

Seasonal jobs that keep the show going

The difference between a fortnight of colour and five months of it comes down to routine maintenance.

• Deadhead weekly from June onwards, cutting each spent flower stem back to a strong bud or leaf joint. This is the single biggest factor in prolonging flowering.
• Try the Chelsea chop in late May: cut one in three stems of rudbeckia and later salvias back by a third. You get bushier plants and flowers staggered over several extra weeks.
• Water deeply twice a week in dry spells, and daily for containers in hot weather. A thorough soak beats a daily sprinkle every time.
• Feed with a balanced granular fertiliser in spring, then switch to a high-potash liquid feed from June to August to keep flower production going.
• Mulch 5–8cm of well-rotted organic matter in spring, keeping it clear of the crowns, and divide any clump that flowers poorly or dies out in the centre.

Do that, and your small space will be delivering colour long after the bedding plants have given up.