4. Choose crops by yield per pot, not by what looks appealing
The plants worth a balcony are the ones that are expensive to buy, quick to crop, or keep producing from a single planting. The ones that waste your space are cheap in shops and need ground.
Start with the reliable group. Cut-and-come-again salad leaves are the highest-value crop on a balcony: sow a trough every three weeks, cut with scissors an inch above the crown, and each sowing gives three or four cuts. Herbs are next — basil, parsley, coriander, chives, mint and thyme together replace a serious amount of supermarket spend, and mint must go in its own pot or it will take over every other one. Spring onions, radishes and rocket all go from seed to plate in four to six weeks.
Then the main crops if you have the sun. Cherry tomatoes, especially bush or tumbling varieties, crop heavily in a 15-litre pot. Chillies and peppers do well in the same size and keep going indoors on a windowsill late in the season. Climbing French beans on a cane wigwam use vertical space rather than floor. Strawberries suit a railing planter or a hanging basket and crop for years.
What to skip: sweetcorn needs a block of plants to pollinate, pumpkins and squash sprawl for metres, maincrop potatoes cost pennies in a shop, brassicas are slow and need netting, and full-size carrots need depth most balconies cannot spare.
Buy plug plants rather than seed for tomatoes, peppers and chillies in a first year. Seed is cheaper but needs heat and light in February, and a failed windowsill sowing puts most people off the whole project.