Why a balcony is a proper wildlife patch

A balcony is not a compromise. It is a different habitat, and in some ways a better one. You are higher up, away from the slug pressure that flattens a young seedling in a border overnight. You catch more sun and more wind. Warmth lingers in brick and railings after the sun has gone down, which suits late-foraging bumblebees. If you have space for four or five deep pots, you have space for a genuine little patch of wildflowers — and once those flowers open, the insects find them with remarkable speed. A window box of cornflowers on a third-floor balcony in a town centre will pull in red-tailed bumblebees, hoverflies and, if you are lucky, a hummingbird hawk-moth. Get the basics right and it becomes a small, dense, reliable pit stop on a route that other people's gardens have left patchy.

Three flowers that do the heavy lifting

Start with plants that feed insects and cope with the specific pressures of a balcony: drying wind, restricted roots, and reflected heat from walls and glass.

• Cornflower (Centaurea cyanus) — a hardy annual, quick from seed, flowering in roughly twelve to fourteen weeks. The open, flat flowers are easy landing pads for bees, and goldfinches will take the seeds if you leave the heads on. Sow in March or April for summer flowers, or in September for sturdier plants that bloom earlier the following year.
• Ox-eye daisy (Leucanthemum vulgare) — a perennial with a taproot, so give it depth rather than width. Long-flowering, drought-tolerant once established, and a favourite with small beetles and hoverflies. Cut it back hard after the first flush and it will often give you a second, shorter flush in late summer.
• Bird's-foot trefoil (Lotus corniculatus) — low, sprawling, and the food plant for common blue caterpillars. It fixes its own nitrogen, so it does not need feeding, and its yellow-and-orange pea flowers keep going from May to September.

If you have room for more, add field scabious, yarrow, viper's bugloss and wild marjoram. All are drought-tolerant and all are nectar-rich.

Pots, compost and the drainage question

Size matters more than beauty. Aim for pots at least 30cm across and 35–40cm deep for the daisies and trefoil; a 45cm depth gives roots room to keep going through a July heatwave. Terracotta dries out faster than glazed ceramic or plastic, which is worth knowing before you buy a matching set in the sale.

Use a peat-free compost, ideally a mix — roughly two parts peat-free multi-purpose to one part soil-based compost such as a John Innes No. 2. The loam holds water and nutrients, and it gives the whole pot more weight so it does not skate across the balcony in a gust. Add a handful of horticultural grit or perlite for drainage, and put a layer of broken crocks or gravel in the base.

Top-dress the surface with 2cm of gravel or bark. It slows evaporation, keeps seeds from splashing out, and stops cats from treating the pot as a litter tray.

Watering: where most balconies go wrong

Balcony containers dry out faster than anything in the ground — wind strips moisture from the compost surface and leaves. In a hot spell you may need to water once a day, sometimes twice. The mistake is little and often: a daily dribble wets only the top inch, and the roots below stay dry while the surface looks damp.

• Water thoroughly until it runs out of the drainage holes, then stop.
• Water in the early morning or evening, never at midday in full sun.
• Check by pushing a finger in to the second knuckle. If it is dry down there, it needs water regardless of how the surface looks.
• Stand pots in saucers in hot weather, but empty them after an hour so roots do not sit in stagnant water.
• Group pots together — they shade each other and the whole cluster holds humidity.

If you are away often, a self-watering container with a reservoir takes a lot of the anxiety out of August.

Looking after them through the year

Deadhead the cornflowers and daisies to keep flowers coming, but stop in late August and let the last heads ripen. Leave the seedheads standing over winter — they look good in frost, and the birds will work through them. Cut perennials back to about 10cm in early spring, before new growth starts. Do not feed wildflowers heavily; a weak liquid feed once a fortnight through the flowering season is plenty, and over-rich compost gives you floppy leaves and few flowers.

What the birds take, and how to help

Garden birds need insects far more than they need seed, especially through the breeding season, when a pair of blue tits may bring several hundred caterpillars a day to a nest. That is the strongest argument for leaving the aphids alone. Do not spray. A few greenfly on the trefoil will feed hoverfly larvae and ladybirds, which in turn become food for chicks.

Add a shallow dish of water — no more than 3cm deep, with a couple of pebbles in it so nothing drowns — and refresh it daily. Site it where a cat cannot sit in ambush. Keep feeders clean and washed weekly with hot soapy water, and if you use them, place them a metre or two away from the pots so the birds do not foul the flowers.

Do those things and a balcony becomes something more than decoration: a small, high, well-stocked larder for the wildlife that passes your window every day.