Oliver Radcliffe
Choose varieties that can cope with a British summer
In a cool climate, the tomato you grow outdoors has to be tough. It needs to ripen quickly, tolerate the odd cold night, and — above all — stand a fighting chance against blight. That disease, Phytophthora infestans, is what ends most outdoor tomato seasons during a wet August, turning healthy foliage black and collapsing the plants within days. Choosing resistant varieties is the single most useful decision you will make.
Look for types bred with blight resistance built in. Crimson Crush, Mountain Magic and Ferline are all reliable croppers in the open, and Lizzano — a compact bush variety — does well in a large pot on a sheltered patio. Cherry and small plum tomatoes ripen faster than big beefsteaks, so if your season is short, favour those. Gardeners' Delight remains hard to beat for flavour, and a plum such as Roma gives you plenty of fruit for sauces and roasting.
If your plot is exposed and windy, lean towards bush (determinate) varieties. They stay shorter, need no staking and suffer less from wind rock than tall cordons.
Start your seeds under cover
Tomatoes need a long season, so give them a head start indoors. Sow from late February to mid-March in modules or small pots of peat-free compost, at about 18–21°C. Germination takes seven to ten days. As soon as the seedlings show, move them somewhere bright — a south-facing windowsill or a heated propagator lid removed — because poor light now produces pale, leggy plants that never quite recover.
Prick them out into 9cm pots once the first true leaves appear, and grow them on at around 15–18°C. Slightly cooler conditions make for stockier, tougher plants than a hot windowsill.
Resist the temptation to plant out early. Tomatoes stall below about 10°C, and cold nights cause blossom drop and those disappointing plants that flower but never set fruit. Harden them off over seven to ten days, putting them outside in a sheltered spot by day and bringing them back in at night. Plant out after the last expected frost — late May in southern England, early June further north and in Scotland.
Find the warmest corner you have
A south-facing wall is worth its weight in gold. Brick and stone absorb heat through the day and release it overnight, giving you a microclimate several degrees kinder than the open plot. Plant about 30cm from the wall, and set cordons 45–60cm apart so air can move between them.
If you are lucky enough to have a polytunnel or greenhouse, use it — even an unheated one transforms results. Grow plants in the border soil rather than pots, which dry out and fluctuate in temperature, and open vents on warm days to keep humidity down.
When planting, bury the stem up to the first set of leaves. Tomatoes root along the buried stem, giving you a stronger plant. Water in well and stake cordons immediately, before the roots settle.
Water steadily and feed at the right moment
Irregular watering is the main cause of blossom end rot, the sunken black patch on the base of the fruit. It is not a disease but a calcium uptake problem, triggered by soil that swings between bone dry and soaking. Water little and often, preferably in the morning, and mulch with compost or grass clippings to hold moisture.
Begin feeding once the first truss has set fruit — not before, or you will get lush leaves and few tomatoes. A high-potash tomato feed once a week is ample. Pinch out the sideshoots on cordon varieties weekly: these are the little shoots growing in the angle between a leaf and the main stem, and they sap energy without producing fruit. Leave bush varieties alone.
Keep blight at bay and ripen the harvest
Blight spreads in warm, humid spells, so keep an eye on the forecast in July and August. Remove any affected leaves the moment you spot them, bag them and put them in the bin — never on the compost heap. If blight reaches the stem, harvest what you have and ripen it indoors.
Simple measures help a great deal: water the soil rather than the foliage, strip the lower leaves up to the first truss to improve airflow, and avoid overcrowding. A makeshift polythene canopy over outdoor plants keeps rain off the leaves and can buy you several extra weeks.
In late August, stop cordons two trusses above the last set fruit and cut watering back as the tomatoes colour. Fruit ripens from the bottom of the plant upwards. Pick at first blush and finish them on a sunny windowsill, or in a drawer with a ripe banana — the ethylene it releases speeds things along.
Before the first frost, bring in anything still green. Lay the fruit in a single layer in a paper-lined box somewhere cool and dark, and check it every few days. Whatever refuses to ripen makes excellent green tomato chutney, so nothing goes to waste.
