Growing Tomatoes Outdoors in a Cooler Climate

The Honest Truth About Outdoor Tomatoes

Tomatoes grown in the open in Britain will never crop as heavily as those under glass, and that is perfectly fine. What you lose in bulk you gain in flavour, and a bowl of fruit ripened against a sun-warmed wall tastes of summer in a way that shop-bought never does. The secret is to work with the climate rather than against it: choose early, tough varieties, give the plants the warmest corner you have, and be ready to hurry the last fruits along when the nights turn cold. Get those three things right and a decent crop is well within reach, even in a soggy, indifferent summer.

Choose Varieties That Can Take Our Weather

Blight is the great enemy of outdoor tomatoes in Britain, and a wet August can wipe out an unprotected crop in a fortnight. Start with varieties bred to resist it. Ferline and Fantasio have both earned their place on windy allotments, and the newer Crimson Crush family carries strong blight resistance alongside a proper beefsteak flavour.

Ripening speed matters as much as disease resistance. Bush, or determinate, varieties tend to be earlier and need far less fiddling about with sideshoots and canes, which suits an exposed plot. Cherry types are the safest bet of all — small fruits ripen quickly and will usually give you something to pick even after a poor July.

• Red Alert — an early bush cherry that crops well even in a wet northern summer.
• Orkado — compact, early, and perfectly happy in a large pot.
• Romello — a reliable plum type for sauces and chutney.
• Tumbling Tom — trailing, cheerful, and content in a hanging basket by the door.
• Mountain Magic — small, dark and notably blight-resistant.

Grow two or three varieties rather than one. If the weather suits a cherry and spoils a beefsteak, you will still have a basket to carry indoors.

Raising Strong Young Plants

Sow indoors from late February to the end of March, in a warm spot at around 18–21°C. Once the seedlings have their first true leaves, prick them out into individual pots and grow them on somewhere cooler and bright, around 15°C. Strong, slightly stocky plants settle into the garden far better than leggy ones raised in a warm, dim room.

Harden them off properly. Over seven to ten days, put the pots outside in a sheltered spot during the day and bring them in at night, gradually extending the time they spend outdoors. Rushing this stage sets plants back for weeks.

Do not plant out until the soil has warmed and night temperatures are reliably above 10°C. In the south that is usually late May; in northern England, Scotland and Wales, early June is safer. Cold nights cause blossom drop, and no amount of later sunshine brings those flowers back.

Find the Warmest, Most Sheltered Corner

Tomatoes want sun from morning to evening and shelter from wind. A south- or south-west-facing wall is ideal — brick and stone hold the day's heat and release it slowly overnight. Failing that, a fence, hedge or even a row of lavender will take the sting out of the wind.

Avoid the bottom of a slope, where cold air pools and the first frosts strike hardest. Raised beds warm up earlier in spring, and a large pot — at least 30cm across — can be moved to follow the sun or shifted under cover when frost threatens. A dark-coloured container, or a sheet of black plastic laid over the soil a fortnight before planting, will raise the temperature noticeably.

Mulch once the ground is warm, using grass cuttings, straw or well-rotted compost. This keeps moisture steady, which matters more than most gardeners realise.

Planting Out and Everyday Care

Plant deeply, burying the stem up to the lowest leaves; tomatoes will root along it and anchor themselves well. Water in thoroughly, then leave them be for a few days.

Cordon varieties need a stout cane and soft twine, tied loosely so the stem can swell. Pinch out the sideshoots that appear in the leaf joints, and in late July stop the growing tip two or three trusses above the last set of flowers — any fruit set after that will not ripen before autumn anyway. Bush varieties need no pinching at all.

Start feeding when the first truss has set, giving a high-potash tomato feed or diluted comfrey once a week. Water little and often rather than in occasional floods; uneven watering is the usual cause of blossom end rot, those dark sunken patches at the base of the fruit.

Ripening Before the First Frosts

From late August, ease off the watering and stop feeding altogether. Strip the leaves below the lowest truss so light and air reach the fruit, and pinch out any late flowers, which will come to nothing.

Watch the forecast. A sheet of horticultural fleece or a cloche will buy you a fortnight of ripening, and tomatoes shrug off a light chill better than you might think. Fruits that have reached full size will ripen off the plant: pick them at the first sign of colour and lay them on a sunny windowsill, or in a paper bag with a ripe banana, which speeds things along nicely.

Whatever is still green when the first hard frost arrives need not be wasted. Green tomato chutney is a country staple, and sliced green tomatoes fried in a little butter make a fine breakfast. Let one or two of your best fruits ripen fully, then save the seed on a piece of kitchen paper for next spring — a small ritual that closes the year neatly and costs nothing at all.