Start with an Honest Look at Your Space

Before you buy a single pot, spend a week watching your balcony. Which way does it face? A south-facing balcony will bake in summer and dry out fast, while a north-facing one may stay cool and shady for most of the day. Note how many hours of direct sun the floor and the railing get, and whether the wind whips through from a particular direction. A fifth-floor balcony beside a main road will behave quite differently from a sheltered ground-floor terrace tucked behind a hedge.

This reconnaissance matters more than any plant list. Herbs such as rosemary, thyme, sage, oregano and lavender want at least six hours of sun a day and will sulk in shade. Mint, chives, parsley and coriander are far more forgiving of a dim corner. If your balcony is a wind tunnel, you will need tough, narrow-leaved plants that shed the breeze rather than catch it — think sea thrift, lavender, ornamental grasses and hardy geraniums.

Measure the floor area and, just as importantly, the railing height. A balcony that feels cramped on the ground can still be wonderfully productive if you use vertical space with tiered planters, hanging baskets and railing troughs.

Choosing Pots That Can Take the Weather

Balcony containers live a hard life. They freeze, thaw, bake and get shoved about by gusts. Terracotta looks lovely but cracks in a hard frost and dries out quickly; if you love the look, line the inside with a plastic pot or choose frost-proof glazed ceramic instead. Glazed stoneware, heavy-duty plastic and fibreglass all cope well. Whatever you pick, weight is your friend — a lightweight pot with a top-heavy shrub is an accident waiting to happen on a windy day.

Size matters more than you might think. Small pots dry out within hours in July and leave roots cooking against hot walls. Aim for these minimums:

• Herbs: 20–25cm diameter per plant, or a 40cm trough for three or four.
• Bushy flowers: 30cm diameter, with at least 25cm of depth.
• Small shrubs or standard bays: 40–45cm diameter, planted in a pot you can still shift with a sack trolley.
• Trailing plants: 25cm baskets, but be prepared to water twice daily in hot spells.

Every pot needs drainage holes, and a centimetre or two of crocks or gravel at the base keeps them clear. Raise pots onto feet or bricks so water escapes freely and air circulates underneath.

Lightweight Compost and Feeding

You are not filling a border, so you can afford a good-quality peat-free multipurpose compost rather than garden soil, which is heavy, drains poorly in pots and may carry weeds. To keep the load down on a balcony with a weight limit, mix in around a quarter by volume of perlite or coarse horticultural grit, plus a few handfuls of composted bark. This gives you a compost that holds moisture without becoming a soggy brick.

Because container plants are watered constantly, nutrients wash straight through. Start feeding about six weeks after planting, once the compost's own reserves are spent.

• Leafy herbs and flowers: a balanced liquid feed every fortnight through spring and summer.
• Flowering plants: switch to a high-potash tomato feed once buds appear to keep blooms coming.
• Mediterranean herbs: go easy. Rosemary and thyme prefer lean conditions and lose flavour and scent when overfed.

Top-dress pots each spring with a couple of centimetres of fresh compost to replace what has slumped and been lost.

Planting for Wind, Sun and Shade

Group plants by their needs rather than by colour, then arrange the pots so the tallest sit at the back or against the wall, with trailers spilling over the front. That layering gives you the look of a border without the depth.

For a sunny, exposed balcony, build the backbone from rosemary, lavender, thyme, sage and ornamental grasses such as blue fescue. Add colour with pelargoniums, osteospermum, verbena and the tough little diascias. Herbs that earn their place in the kitchen and look good doing it include golden oregano, purple sage and variegated thyme.

For shade, rely on mint, chives, parsley, sweet woodruff and hardy geraniums, plus ferns, hostas and ivy for foliage. If wind is your main problem, plant a low hedge of lavender or a screen of bamboo in a long trough along the railing — it will shelter everything behind it. Fix all troughs and baskets with proper brackets, and check them after every gale.

Watering Without the Faff

Regular watering is the single thing that separates a thriving balcony garden from a sad collection of sticks. In July, a sunny balcony can need watering twice a day, morning and evening. Water until it runs out of the drainage holes rather than giving a token splash, and water the compost, not the leaves.

• Push a finger 3cm into the compost. If it is dry at that depth, water.
• Use self-watering reservoirs or a simple drip kit if you travel or work long days.
• Group pots together to shade one another and slow evaporation.
• Mulch the surface with gravel or bark chippings to lock in moisture.
• Move the thirstiest pots into afternoon shade during heatwaves.

Deadhead flowers weekly to keep them blooming, and pick herbs little and often — that constant harvesting is what keeps them bushy and productive. Repot into a size up every couple of years, and by the second summer you will have a small, fragrant, edible garden that earns its keep far beyond its footprint.