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Tomatoes are sun-worshippers, and in Britain the warmest, most sheltered spot in the garden is often the patio. A south or south-west facing wall or fence soaks up heat during the day and releases it slowly overnight, which is exactly what ripening fruit needs. Grown in open ground, tomatoes can sulk in our cool, damp summers; grown in a pot against a warm wall, they can be moved into shelter when the weather turns, watered precisely and given compost that is far richer than most borders can offer.
The other advantage is control. In a container you decide exactly what the plant eats and drinks, and you can whisk it under cover at the first sign of blight. The trade-off is that pots dry out quickly and nutrients leach away with every watering, so success depends on three things: generous container size, good compost, and a watering routine you can actually keep up with.
Size really does matter. A tomato in a small pot will produce small, split fruit, no matter how lovingly you feed it. Aim for a minimum of 10–15 litres of compost per plant — roughly a 30–35cm diameter pot or a standard grow bag with two plants at most. Bush varieties, sometimes called determinate, cope with slightly less; tall cordon varieties need more. Terracotta looks lovely but dries out fast, so glazed ceramic, plastic or fabric pots are more forgiving. Whatever you choose, check there are proper drainage holes and stand the pot on feet or bricks so water can escape freely.
Fill with a quality peat-free multipurpose compost, or a soil-based John Innes No. 2 if you want a little more weight and water-holding capacity. Mix in a couple of handfuls of well-rotted garden compost or worm castings, plus a slow-release general fertiliser. Never reuse last year's compost for tomatoes: it will be exhausted and may harbour disease. A layer of gravel or broken crocks in the base of the pot helps drainage, though a saucer is useful in high summer to hold a little reservoir.
Wait until the last frost has passed — usually late May in southern England, early June further north — before moving plants outside. Harden them off over a week, bringing them in at night at first. Plant deeply, burying the stem up to the first set of true leaves: tomatoes will grow roots along the buried stem, giving you a stronger plant. Water in well and keep the pot in its final position from the start.
Put the support in at planting time, not later, so you don't spear the rootball. A sturdy bamboo cane, a spiral metal support or a length of twine tied to a bracket on the wall all work well. Tie cordon plants loosely with soft string every 20–25cm as they grow, using a figure-of-eight loop so the stem isn't pinched. Pinch out the side shoots that appear in the angle between leaf and stem on cordon varieties — they divert energy from fruit. Bush varieties need no pinching; just let them sprawl.
Irregular watering is the single biggest cause of split skins and blossom end rot. Little and often beats a weekly flood. In July and August, a pot in full sun may need water twice a day — morning and early evening — and a mulch of grass clippings, compost or bark on the surface will slow evaporation. Water at the base, never over the leaves, to keep foliage dry and reduce the risk of blight and mould.
Start feeding once the first truss of flowers has set fruit. Use a high-potash tomato feed at the strength recommended on the bottle, once a week at first, then twice weekly as the plant loads up. If leaves turn yellow between the veins, a dose of magnesium sulphate, available from any garden centre, usually corrects it. Keep feeding until the last fruits are picked; stopping too early gives you mealy, tasteless tomatoes.
British summers test tomato growers. Keep an eye on the forecast: if heavy rain is due, move pots under an overhang, as wet foliage in warm weather is an invitation to blight. Sheltering pots from strong wind also prevents snapped stems and battered leaves. Watch for aphids on soft growth — a firm spray with water dislodges most of them — and check the undersides of leaves for whitefly, which thrive in still, warm corners.
By late August, pinch out the growing tip of cordon plants so the plant puts its energy into ripening what's there rather than starting new trusses that will never finish. As nights cool, lay green fruit in a single layer in a paper-lined drawer or cardboard box with a ripe banana, or bring whole trusses indoors to a sunny windowsill. Fruits picked slightly underripe will colour up perfectly well in a warm kitchen, and green tomatoes make excellent chutney if the season runs out before the sun does.
Garden Cove shares practical, down-to-earth guidance on coastal and small-space gardening for uk homes for readers across the UK.
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