How to Grow Tomatoes

Tomatoes are tender, sub-tropical plants that thrive in the warm, sheltered conditions a greenhouse provides, usually cropping earlier and for longer than they would outside. They also grow happily outdoors in a hot summer, given the right variety and a sunny site. We go through both routes below

 

Different types of tomatoes to grow

Tomatoes come in two groups; cordon and bush:

Cordon (indeterminate)

Grows as a single main stem that keeps going upward all season. They need staking or a string to climb. Great for greenhouse growing.

Bush (determinate)

Grows to a set height, stops on its own, and doesn't need side shooting. More compact and self-managing. Good for containers, raised beds, or outdoors without much fuss. 

 

Growing tomatoes in the greenhouse

 

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Growing tomatoes from seed in the greenhouse

Growing tomatoes opens up a huge range of heritage and unusual varieties you never see as young plants. It takes a little more care in late winter, but is well worth it.

 

Top Tip: Resist sowing too many: even half a dozen plants will keep a household in tomatoes all summer.

 

For a greenhouse crop, sow tomatoes from late February to mid-March. Fill small pots or modular trays with moist, peat-free seed compost and sow about 1cm deep. Tomato seed needs around 18 degrees C to germinate, so use a heated propagator, or stand the pots on staging or shelves with a clear plastic bag over the top to hold in humidity. Seedlings usually appear within a fortnight.

In an unheated greenhouse, hold off sowing until the cold has passed, or start the seed indoors and move plants out once it warms up.

As soon as the seedlings show, uncover them and give them as much light as possible to stop them growing thin and leggy. Greenhouse shelving or a seedrack lifts the trays off a cold floor and keeps them close to the glass where the light is best. In a cold spring, a little background warmth from a greenhouse heater keeps tender seedlings safe on chilly nights.

Once each seedling has its first pair of true leaves, prick it out into its own 9cm pot (roughly) of peat-free compost, holding it by a leaf rather than the stem. Plant any leggy seedling deeper, so the lowest leaves sit just above the compost and the buried stem can root. Keep potting on as the plants grow, somewhere bright and no cooler than 16 degrees C.

They should be ready to go into their final position about a month later. Most tomatoes take roughly six to eight weeks from sowing to planting out, then another seven or eight weeks before the first fruits ripen.

Before tomatoes go anywhere cooler than the greenhouse, harden them off by standing them outside during the day for a week or two and bringing them back under cover overnight. This gets them used to outdoor conditions gradually.

 

 

Growing tomatoes from young plants in the greenhouse

If you would rather skip the seed stage, buying young plants is quick and easy. Shop bought plants cost more but tend to be more vigorous, crop earlier and resist disease better. 

Top Top - Whatever you buy, look for sturdy, dark-green plants and check the label to see whether it is a cordon or a bush type, as the two are grown differently.

Do not put a newly bought plant straight outside until it has been hardened off and the weather is reliably warm, though in the greenhouse you can plant a little earlier. Tomatoes do beautifully in large containers and grow bags as well as a greenhouse border, and are wonderfully productive grown in pots in a small space. Use one plant per pot of at least 30cm (up to 45cm for a big cordon), or two per standard grow bag, filled with peat-free compost. Whichever you choose, collecting rainwater in a water butt gives you a steady, soft supply for the thirsty weeks ahead.

Caring for greenhouse tomatoes

Cordon tomatoes can reach 1.8m or more, so support them from the outset. Tie the main stem loosely to a tall cane at regular intervals, or wind it gently around a vertical string tied to a roof brace and anchored under the rootball at planting time. Tomatoes do not cling on their own, so you will need to tie or wind them in as they grow.

On cordons, pinch out the side-shoots that sprout from the joint between each leaf and the main stem, while they are small. Left alone they form a sprawling mass that is hard to support and produces little fruit, so check each time you water.T

Top Tip: When a cordon reaches the top of its support, or has set seven trusses in the greenhouse, pinch out the growing tip two leaves above the top truss. Bush types need no side-shooting; just add a short cane if a laden stem droops.

 

Watering tomatoes in a greenhouse

Watering is the single most important job. Keep the soil or compost evenly moist, watering little and often rather than letting plants dry out and then drowning them. Erratic watering is the main cause of blossom end rot and split fruit.

Plants in pots and grow bags dry out fast and may need watering daily in hot spells. Once the first fruits start to swell, feed every week to two weeks with a high-potassium tomato feed to encourage flowering and fruiting.

Cordon Tomato Variety

 

Top Tip: 

Tomato roots do different jobs at different depths. Finer feeder roots sit near the surface, deeper roots handle water uptake. With that in mind, apply liquid feed to the top of the compost, but water from the bottom by sitting the pot in a tray or capillary matting. It keeps nutrients where the plant can use them and encourages roots to seek out moisture rather than relying on surface watering.

A good extension of this is a simple reservoir setup. Sit pots on gravel over a tray or capillary matting that stays consistently wet. The plant drinks when it needs to, which helps avoid the uneven watering that causes split fruit and blossom end rot.

 

Caring for tomatoes in a greenhouse

Greenhouses can get fiercely hot in high summer, which stresses plants and stops fruit setting. Open vents and doors on warm days and fit blinds or shading to take the edge off the heat. Good ventilation also lets pollinating insects reach the flowers; on still days you can lightly tap or shake the flowering trusses, or mist them, to help the pollen transfer. Damping down the floor on hot days raises the humidity and keeps red spider mite at bay.

 

Growing tomatoes in raised beds and outdoors (from seed and plants)

 

If we’re honest, with the unpredictable nature of the UK climate, it is much safer to sow tomatoes indoors, on a sunny windowsill if you don't have access to a greenhouse. Once they are young plants though you do not need a greenhouse to grow good tomatoes.

In a warm summer they crop well outdoors in a raised bed, in the open ground, or in pots and grow bags on a sunny patio. A raised bed warms quickly in spring, drains freely and lifts plants away from soil-borne trouble, all of which suits tomatoes. 

Top tip: The crucial rule outdoors is frost: tomatoes are tender and will not survive even a light one, so when to plant out tomatoes comes down to your last frost date.

Where to position tomatoes outside

Tomatoes need all the warmth and light they can get, so choose your warmest, sunniest, most sheltered spot, ideally against a sunny wall that traps heat. Full sun is essential. Avoid exposed, windy sites that rock and snap tall plants, and steer clear of frost pockets. A south-facing raised bed or a row of grow bags on a sheltered patio are both excellent.

 

Watering, soil, spacing and supporting tomatoes outdoors

Soil: tomatoes are hungry, thirsty plants that love rich, free-draining but moisture-retentive soil. Plant deeply, with the first leaves just above the soil so the buried stem roots. Avoid the same ground two years running, to stop soil diseases building up.

Spacing and support: set plants 45 to 60cm apart, in rows if you have several, checking the packet as larger varieties need more room. For cordons, push a sturdy cane in next to each plant at planting time and tie the stem in loosely as it grows, removing side-shoots and snipping the main stem after about four trusses outdoors, where the season is too short to ripen more. 

For growing tomatoes in grow bags or pots, use one plant per 30cm-plus pot or two per grow bag. Bush types need little or no support and are the easiest choice for containers. Our month-by-month raised bed guide sets out the seasonal jobs in more detail.

Watering: consistency is everything. Water regularly and evenly to keep the soil steadily moist, as the swings between bone dry and sodden are what cause splitting and blossom end rot. Containers may need daily watering in hot weather. A useful trick is to sink a pot into the ground beside each plant and water into that, so moisture goes straight to the roots rather than sitting around the stem.

 

 

The best tomato companion plants

A little companion planting helps an outdoor tomato patch look after itself. Basil is the classic partner, said to help deter pests and a perfect flavour match on the plate; French marigolds are some of the best companions of all, repelling whitefly and nematodes; and nasturtiums act as a sacrificial trap crop that lures aphids away from your tomatoes. Chives and borage are useful neighbours too, drawing in pollinators and beneficial insects.

It pays to know what to keep apart as well. Do not grow tomatoes next to potatoes, as the two share the same blight and planting them together helps the disease spread. Keep brassicas such as cabbage and broccoli away, since they compete hard for the same nutrients, and avoid fennel, which releases compounds that inhibit the growth of most nearby plants.

 

When and how to harvest tomatoes when they're outside

Outdoor tomatoes ripen a little later than greenhouse ones, usually from August into early October. Pick each fruit as it colours up fully and comes away easily, checking the plants every few days through the season. As nights cool and blight risk rises, bring in the last of the crop rather than leaving it on the plant.

Tomato pests and problems and how to avoid them

Given warmth and steady moisture, tomatoes are easy and healthy. Most problems come from erratic watering or poor air flow, so good habits prevent the majority of them. Here are the ones worth knowing, including the common problems when growing tomatoes in a greenhouse.

Blossom end rot shows as a hard, sunken, blackened patch on the base of the fruit. It is caused by irregular watering, which stops the plant taking up calcium, rather than by disease. The cure is prevention: water little and often to keep moisture steady, and never let pots dry out completely.

Fruit splitting and cracking happens when a dry spell is followed by a sudden flush of water, swelling the fruit faster than the skin can grow. Once again, consistent watering is the answer. Pick fruit promptly as it ripens, before it has a chance to split.

Tomato blight is the main threat outdoors, much more so than under glass. It thrives in warm, wet weather, turning leaves brown and mottled and spreading dark, sunken patches over the fruit. Affected plants should be removed and binned, not composted. To avoid it, grow blight-tolerant varieties, keep plants under cover where you can, space them for good air flow, and remove the lower leaves as fruit sets to improve ventilation around the base.

 

Cooking with tomatoes

There is no better reward for a summer of growing than a bowl of your own ripe tomatoes. Eat them simply, sliced with a little olive oil and salt, or put a glut to good use with one of these recipes from chef Gill Meller on the Rhino blog:

• A roast tomato sauce for everything, slow-roasted with garlic and thyme, then sieved into a rich sauce you can freeze

• Plum, tomato, beetroot, red onion and mint salad, a fresh raw salad that makes the most of a summer harvest

If you have more tomatoes than you can eat, the roast sauce freezes beautifully, while whole fruit keeps best at room temperature out of the fridge, where the cold dulls the flavour. Any green tomatoes left at the end of the season will ripen on a sunny windowsill, or make excellent chutney.

Growing tomatoes is one of the simple joys of the gardening year. Give them warmth, a sunny spot and a steady drink, and they will repay you generously all summer. Once you have the hang of them, you might branch out into cucumbers under the same glass, or try a perennial like asparagus in the bed next door.