Tomato

The tomato came out of the western coast of South America, was domesticated in Mesoamerica and reached Europe in the sixteenth century, where it was grown as an ornamental curiosity for two hundred years before anyone would eat it. It is now the most widely grown garden vegetable in the world, and it is the plant that teaches new gardeners the most, because it responds visibly to everything you do and does not forgive irregular attention.

Sowing and the frost date

Tomatoes are killed by frost and sulk below 10 degrees, so the whole calendar is built backwards from the last frost in spring. Sow indoors about six weeks before that date, in warmth, at around 20 degrees, and keep the seedlings in the brightest place you have or they stretch immediately.

In a temperate northern garden that means sowing February to April. In a temperate to warm temperate southern garden it means August to November, with the exact date depending on your own last frost far more than on the month. In frost free subtropical areas, in either hemisphere, the timing is set by heat instead: plants sown to fruit through midsummer often set poorly, because pollen fails above about 32 degrees.

Pot the seedlings on into individual pots as soon as they have their first true leaves, and plant out after the last frost, burying the stem deeper than it was; a tomato roots from its buried stem and makes a stronger plant.

Light

Six to eight hours of direct sun. There is no way around this one. Less light means fewer flowers, later fruit and noticeably thinner flavour.

Water

This is the plant in this journal that wants the most water and the most regularity. A fruiting plant in a pot in hot weather may want watering twice a day. Water at the base, in the morning, and mulch the surface to slow evaporation.

Evenness matters more than volume. A plant that dries out and is then soaked splits its fruit, because the flesh swells faster than the skin can stretch, and it develops blossom end rot, the dark sunken patch on the base of the fruit that people mistake for a disease. It is a plumbing problem: calcium cannot reach the fruit through a plant whose water supply keeps stopping.

Feeding

Use a balanced feed while the plant is making stems and leaves, then switch to a high potassium tomato feed once the first truss of flowers appears, weekly or fortnightly to the end of the season. Too much nitrogen late on gives a large green plant with little fruit.

Cordon or bush

Cordon, also called indeterminate, varieties grow up one stem indefinitely and need a support and regular removal of the side shoots that appear where a leaf joins the stem. Bush, or determinate, varieties stop at a set height, carry their fruit in a rush and should not be pinched at all. The label tells you which you have, and treating one like the other is the commonest beginner mistake.

Harvesting

Pick when the fruit has full colour and gives very slightly to a squeeze, roughly July to October in the north and December to April in the south. Fruit picked slightly under ripe finishes indoors, but never in the fridge, which flattens the flavour permanently. At the end of the season, green fruit ripens indoors beside a banana.

Ailments

Blossom end rot and splitting are both watering problems. Blight is the serious disease and moves fast in a wet season, so outdoor plants in a damp summer need air, base watering and the affected leaves removed at once. The ledger below has the rest.