Start with the sunniest spot you have

Butterflies are cold-blooded, so the warmest corner of your garden will always be the busiest. A border that catches sun from mid-morning until late afternoon, sheltered from strong wind by a hedge, fence or wall, will support far more life than a larger bed in shade. Spend an hour watching it on a sunny day before you plant anything: butterflies will show you the warm pockets where they like to settle.

Leave a few flat stones or a patch of bare, sun-baked earth. Butterflies need to bask with their wings spread before they can fly, feed and mate, and a warm slab of stone is as important to them as any flower.

Nectar plants for adult butterflies

Adults need sugar, and they are surprisingly fussy about how they get it. Single, open flowers with a landing platform and easy access to nectar are ideal; double blooms and highly bred bedding plants are usually useless. Aim for something in flower from April right through to October.

• Spring: wallflowers, especially the long-flowering Bowles's mauve, plus aubrieta, honesty and forget-me-not.
• Early summer: field scabious, catmint, thyme, chives, alliums and hardy geraniums.
• High summer: lavender, marjoram, buddleia, Verbena bonariensis, betony, common knapweed, purple loosestrife and yarrow.
• Late season: asters, sedum, single dahlias, cosmos, rudbeckia and echinacea.

Plant in generous drifts rather than one of everything. Butterflies find blocks of colour from a distance, and a single marjoram plant in July can be smothered with peacocks, commas and small tortoiseshells. Marjoram and lavender are the two hardest-working plants in any butterfly border — if you only make room for a few things, make it these.

The other half of the life cycle: caterpillars

Nectar keeps adults alive, but caterpillars need leaves, and most British species are extremely fussy about which ones. Plant only nectar flowers and you will get visitors; plant larval food too and you get residents. Two groups matter most in a wildflower border.

• Stinging nettles feed the caterpillars of peacock, small tortoiseshell, red admiral and comma. They want nettles growing lush and young in sunshine, not the tired shade-grown clumps at the back of a shed. In a border, sink a large pot or bottomless bucket into the ground to stop the roots running, or keep a discreet patch tucked behind taller perennials. Cut half of it down in June and the other half in July, in rotation — females prefer to lay on fresh regrowth, and this keeps the patch leafy rather than seeding itself everywhere.
• Native grasses are the food plants of meadow brown, gatekeeper, ringlet, speckled wood and all the skippers. Cocksfoot, Yorkshire fog, meadow foxtail, timothy, red fescue and bent grass are all valuable. A tussocky edge, a metre-wide strip left unmown, or a few clumps woven among perennials will do the job. Leave them standing over winter and cut in late February or early March.

If you have room for more, add bird's-foot trefoil for common blue, garlic mustard or honesty for orange-tip, and holly and ivy nearby for holly blue. Brimstones need alder or purging buckthorn — if there is space for one shrub, that is the one to choose.

Designing it so it works all year

Wildflower borders have a reputation for looking scruffy by August, but that is a design problem rather than an inevitability. Give the planting a skeleton and it will hold together beautifully even as the nettles go over.

• Use tall, see-through plants such as Verbena bonariensis and bronze fennel to knit the border together without blocking light.
• Anchor the back with structural evergreens: rosemary, lavender, cotton lavender or a clipped shrub.
• Cover the ground with geraniums, alyssum and thyme to suppress weeds and shelter insects.
• Let grass tussocks read as a deliberate feature, either as a gravel-garden matrix or in a defined band along the front edge.
• Repeat two or three key plants along the border so the eye reads rhythm rather than randomness.

Maintenance that helps rather than harms

The way you look after a border matters as much as what you plant in it.

• Never use insecticides, including sprays aimed at aphids. Caterpillars are the casualties, and aphids feed the hoverflies and ladybirds that do the work for you.
• Delay cutting back until late February or March. Seedheads feed birds through winter and hollow stems shelter overwintering larvae and pupae.
• Leave some leaf litter and undisturbed soil in corners for pupae to sit out the cold months.
• Keep a shallow dish of damp soil or sand sunk to ground level. Males of many species gather there to take up minerals from damp ground.
• Water new plantings through their first summer, and top up the mulch with garden compost rather than bark, which smothers ground-nesting species.

Sourcing plants and planting them well

Choose British-grown, peat-free plants wherever you can, and look for wildflower plugs of native provenance for the grasses, knapweed, scabious and betony. Autumn is the best time to plant, while the soil is still warm; spring works well too, provided you water diligently through the first summer.

Nettles and native grasses are easy and cheap from seed, and a packet scattered in a prepared patch will give you a caterpillar nursery within a season. Please do not lift wild plants from the countryside — many are legally protected, and most transplants sulk and die anyway.

Give a new border two or three seasons to settle. Then one warm July morning, with a peacock feeding on your marjoram and a ringlet flickering over your tussocks, you will know the whole thing has quietly become a habitat.