Start with a light audit, not a space audit

Before you buy a single pot, spend a day watching your outdoor space. Most vegetables need at least six hours of direct sun, but that window moves through the day and through the seasons. A south-facing balcony can be a sun trap from March to October, while a north-facing courtyard may only manage three or four hours even in midsummer. Note where the sun actually lands at 10am, 1pm and 4pm — the difference between a courgette crop and a sad, leggy disappointment often comes down to a metre of wall.

Once you know your light, you can plan honestly. Full sun for tomatoes, peppers, courgettes, beans and cucumbers. Partial shade — four hours or so — suits salad leaves, rocket, chard, spinach, radishes and most herbs. Deep shade is for mint, parsley and little else, though even that is worth having when it's fresh from a pot by the door.

Wind matters as much as sun on a balcony. A gusty corner will shred runner beans and snap tomato stems, so plan for a sheltered spot or be ready to rig up a simple screen of netting or trellis.

Containers: bigger is genuinely better

The most common mistake in small-space growing is choosing pots that are too small. A tomato in a 15cm pot will sulk and produce a handful of tiny fruit; the same plant in a 30-litre container will crop for months.

• Salad leaves, herbs, radishes: 15–20cm deep, but wide rather than tall so you can sow a cut-and-come-again patch.
• Bush tomatoes, chillies, dwarf beans: 25–30cm deep and wide, one plant per pot.
• Carrots, beetroot, chard: 30cm of depth minimum. Choose short-rooted carrots such as 'Paris Market' rather than long varieties.
• Courgettes, cucumbers, potatoes: 40–50 litres, one plant only.

Terracotta looks lovely but dries out fast in a British heatwave. Glazed ceramic, plastic or fabric grow bags hold moisture far better, and a layer of gravel or cocoa shell mulch on the surface slows evaporation. Always check for drainage holes — a saucer of standing water will rot roots within a fortnight.

Use a peat-free multipurpose compost and refresh it each spring. Compost loses its structure and nutrients after a season, and tired compost is the quiet cause of most disappointing second-year crops.

Raised beds and grow bags on hardstanding

If your only outdoor surface is paving or concrete, a raised bed is still perfectly possible. Build or buy one around 30cm deep and line the base with a permeable membrane to stop weeds and keep compost in place. Fill it with a mix of about two-thirds multipurpose compost and one-third soil-based compost for weight and water retention — garden soil alone is usually too heavy and often riddled with weed seed.

Put the bed on feet or slatted bearers so water can drain away underneath, and leave a gap against walls for airflow and maintenance. A 1m x 1m bed is surprisingly productive: a row of salad, a row of spring onions, a couple of chard plants and a nasturtium for colour will keep you in leaves from May to October.

Grow bags remain the cheapest route into tomato growing, but do them a favour. Stand them on a tray, cut drainage slits in the base rather than the sides, and plant only two or three tomatoes per bag. Laying a grow bag on its side turns it into a deeper, more stable home for a single courgette or a pair of cucumbers.

Grow up, not out

Vertical space is the most underused asset in urban gardens, and climbing crops are the most generous plants you can grow in a tight footprint.

• Runner and climbing French beans: a wigwam of eight canes in a 40cm pot gives you weeks of picking from July onwards.
• Peas: tall varieties on netting, or dwarf ones such as 'Tom Thumb' in a window box.
• Cucumbers: train the side shoots up a single cane and pinch out the growing tip once it reaches the top of its support.
• Tumbling tomatoes: perfect in hanging baskets and wall planters, where they trail rather than climb.

Fix trellis or netting to a sunny fence or wall with a 5cm gap behind it so plants can be tied in easily and air can circulate. On balconies, use freestanding obelisks and weighted bases rather than drilling into railings. Check your lease before attaching anything to a shared wall.

Crops that genuinely earn their place

In a small space, grow what tastes dramatically better fresh and what costs a lot to buy. Salad leaves, herbs, rocket, cut-and-come-again spinach and chard are all excellent value. Tomatoes, especially heritage varieties, are worth every inch of sun. Sugar snap peas, French beans and strawberries taste nothing like their supermarket equivalents.

Skip maincrop potatoes, parsnips, sweetcorn and anything that demands a long season and a lot of room for a modest return. Save those for an allotment if you ever get one.

Watering, feeding and succession

Containers dry out quickly, so water in the morning when you can — evening watering encourages slugs and mildew. In hot spells, check twice daily by pushing a finger into the compost. A simple drip line or self-watering reservoir pays for itself in a single summer, especially if you go away.

Start feeding once flowers appear. Tomatoes, peppers and cucumbers want a high-potash liquid feed every week or so; leafy crops are happier with a milder, nitrogen-rich feed. Sow a pinch of salad seed every three weeks from March to August for a continuous supply, and keep picking — the more you harvest, the more the plant gives you.