A balcony vegetable garden: starting with what you have

Sun, wind and the wall behind you

Count your hours of direct sun on a clear day in June, not in March. Six hours or more facing south or west means tomatoes, peppers and strawberries are possible. Four to five facing east is enough for lettuce, spinach, chard and nearly all herbs.

The wall behind you cuts both ways. By day it reflects heat back and at night it releases it slowly, which pushes a tomato weeks ahead in a northern summer. In a heatwave that same wall becomes an oven: move pots half a metre forward.

Wind is the underrated factor. There is almost always more of it up high than at ground level, and it dries pots faster than sun does. A reed screen or a row of tall pots on the windward side helps more than you would think.

Pot sizes and weight

For fruiting crops — tomato, pepper, courgette — ten litres is the minimum and fifteen is better. Leaves and herbs manage in five. The smaller the pot, the more often you water; on a sunny balcony in July that is the difference between once and twice a day.

Account for weight. A fifteen-litre pot weighs around twenty kilos wet. Ten of those is two hundred kilos across a few square metres. Most balconies carry that fine, but put heavy pots against the building or over a supporting wall rather than at the edge — and check first on an older balcony or with your building manager.

Stand pots on feet or tiles. Directly on the floor, water pools, which stains, rots roots and cracks pots in a frost.

Watering in summer

A balcony in full sun needs water every day in July and August, twice on the hottest days. That is where most balcony gardens fail: one weekend away is enough.

Bigger pots, a layer of mulch and water reservoirs in the base stretch your margin from half a day to two. Going away longer, a simple drip system on a tap timer is more reliable than a neighbour.

What to sow in year one

Start small: one tomato plant, a trough of loose-leaf lettuce and two pots of herbs. That is enough to learn the rhythm of watering and harvesting without one failure ruining the season.

Sow lettuce and spinach in March and April, and again in late August for an autumn harvest. Start tomatoes indoors in March and only move them out after mid-May.