How to Grow Tomatoes

How to Grow Tomatoes: A Practical Guide from Seed to Harvest

Tomatoes are one of our favourite crops for the greenhouse and the garden. There are so many different flavours, types and colours to choose from. Nothing beats wandering outside and picking and eating them fresh straight from the vine or harvesting and preparing a sauce that can be used in soups and other dishes.

They’re not difficult plants to grow, but they are hungry and thirsty. If you follow this growing advice, you won’t go far wrong. Give them warmth, plenty of light and reasonably consistent care and they’ll reward you with a decent crop.

The first thing to check is whether you’re growing a cordon or bush variety. Cordon tomatoes grow tall and need supporting and pruning, while bush tomatoes form shorter, branching plants and are largely left to get on with it.

When to Sow

Tomatoes need a long growing season, but there’s very little advantage in sowing them too early. Unless you have a heated greenhouse and good light, February-sown seedlings can spend weeks becoming tall and pale or be hit by the cold.

For most gardeners, the middle of March to mid-April is an excellent time to sow tomatoes indoors. There’s increasing daylight, the seedlings grow away strongly, and they’ll still be a good size when planting time arrives.

If you have a greenhouse, you can start a little earlier. For tomatoes you plan to grow outside, a later planting will be better to avoid any late cold snaps in May. When you have grown them for a couple of years, you will soon find the best time in your locality. You can always ask some experienced local gardeners who will help you with timing.

The important thing is warmth. Tomato seeds germinate best somewhere nice and warm, so a propagator or warm windowsill works well.

And don't worry if April arrives and you haven't sown any. Get them started. Tomatoes grow quickly once conditions improve and a healthy later seedling will often overtake one that has struggled through the darker days of early spring.

Sowing and Growing Seedlings

Tomatoes are quite straightforward from seed. Fill a small pot or seed tray with seed compost, firm it gently and space the seeds over the surface. Cover them with roughly half a centimetre of compost or vermiculite, water carefully and put them somewhere warm.

You should see seedlings appearing within a week or two.

As soon as they emerge, light becomes more important than heat. Move them to the brightest place you can find. A warm, gloomy windowsill is how you produce those enormously long seedlings that seem determined to reach the ceiling.

Once the first proper tomato leaves appear, move each seedling into its own small pot. Handle it by a leaf rather than the stem and plant it a little deeper than it was growing before. Tomatoes can produce roots from the buried part of their stem, so slightly leggy seedlings can often be rescued this way.

Keep them somewhere bright and frost-free and water when the compost begins to dry.

Turn windowsill plants regularly too. Otherwise, they'll spend their early lives stretching one way towards the glass.

As they fill their pots with roots, pot them on into something larger. By planting-out time, you want sturdy, stocky plants rather than enormous ones already flowering desperately on the kitchen windowsill.

Planting Out

Tomatoes hate frost, so don't be tempted outside by one lovely warm afternoon in April. Wait until the danger of frost has passed and, for outdoor plants, until nights are reasonably mild. You can tell if they get cold by their purple leaves and their ability to sit and sulk!

Before planting, harden them off for a week or two. Put them outside during the day and bring them back under cover at night, gradually leaving them out for longer. Plants raised indoors have soft growth and need a little time to get used to wind, cooler temperatures and proper sunshine.

Choose the warmest, sunniest position you can give them.

Tomatoes grow happily in the ground, greenhouse borders, large pots or growing bags. If you're using containers, don't go too small. A decent volume of compost makes watering much easier later in summer.

Plant them slightly deeper than they were growing in their pots and water them in well.

If you're growing cordon tomatoes, put the support in at planting time. It's much easier than trying to wrestle a cane past a large root system six weeks later.

Supporting and Pruning

This is where knowing what sort of tomato you're growing really matters.

Cordon, or indeterminate, tomatoes naturally want to keep growing upwards and producing side shoots. Train the main stem up a strong cane, string or other support and tie it in loosely as it grows.

You'll notice little shoots appearing where each leaf joins the main stem. These are the side shoots, and on cordon tomatoes I pinch them out while they're small. Leave them all on and you soon end up with a tomato jungle that's mostly leaves and surprisingly difficult to water.

Check once a week because side shoots have an impressive ability to go from “I'll pinch that out tomorrow” to another entire tomato plant.

Bush, or determinate, varieties are different. Don't remove their side shoots. Their naturally branching habit is where much of the crop develops.

Later in summer, I remove some of the lowest leaves from cordon tomatoes, particularly anything touching the soil. It improves airflow and makes watering easier.

Towards the end of the season, you can also pinch out the growing tip of cordon plants once they have several good trusses of fruit. At that point, I'd rather the plant concentrated on ripening the tomatoes.

Watering and Feeding

If tomatoes could write their own care instructions, “please be consistent” would probably be at the top.

A plant in full growth with fruit developing can drink a surprising amount of water, particularly in a greenhouse or container. Check them regularly and water thoroughly when they need it.

Try not to let plants become bone dry and then absolutely flood them. That cycle is one of the reasons fruits split and can contribute to blossom end rot.

Water the compost or soil rather than soaking the foliage, and if you can, water in the morning. It leaves less humidity hanging around the plants overnight.

Once the first fruits have set, start feeding with a tomato fertiliser according to the instructions on the product. Tomatoes are hungry plants, particularly in pots and growing bags where nutrients are limited.

Don't assume that twice as much feed means twice as many tomatoes. It doesn't.

The best tomato plants aren't necessarily the ones with the darkest green leaves and most enormous growth. You're after a healthy plant carrying plenty of fruit.

Harvesting

This is the bit you've been waiting for.

Pick tomatoes once they've developed their proper colour and feel ripe but still firm. Give the fruit a gentle twist and it should come away easily, although I often use snips for larger trusses rather than risk damaging the plant.

In warm weather you'll probably find yourself picking every few days. And do pick them. Leaving ripe fruit hanging around doesn't improve it and simply gives pests and splitting more opportunity.

Towards the end of summer, remove any flowers that clearly have no chance of producing ripe fruit. You want the plant putting its remaining energy into the tomatoes already there.

If autumn arrives with plenty of green tomatoes still hanging on, don't write them off. Pick sound fruit before frost and bring it indoors to ripen or make them into Green Tomato Chutney.

Enjoy eating tomatoes straight from the vine as you are working in the garden. That's half the point of growing tomatoes in the first place.

Common Problems

Blight is the one tomato growers dread. It tends to arrive during warm, humid weather and causes dark patches on leaves and stems before spreading rapidly through the plant and fruit. Remove affected material promptly. Outdoor tomatoes are particularly vulnerable in wet summers, while keeping greenhouse foliage dry and providing good ventilation helps reduce problems.

Blossom end rot appears as a dark, sunken patch at the bottom of the fruit. It's linked to calcium uptake, but before reaching for a bottle of something, look at your watering. Irregular moisture is very often behind it, particularly with container-grown plants.

Split fruit has much the same story. A dry plant suddenly gets plenty of water, the fruit swells quickly and the skin can't keep up. More consistent watering usually sorts it.

Yellowing lower leaves aren't automatically a disaster. Older leaves naturally deteriorate as the season progresses. Remove them if they're looking tatty, but widespread yellowing deserves a closer look at watering, feeding and root health.

Aphids and whitefly can gather around soft young growth, particularly under glass. Check the undersides of leaves regularly — catching a small infestation is considerably easier than dealing with several generations of it.

You'll also occasionally find flowers that simply drop without setting fruit. Cold nights, excessive heat and poor pollination can all be responsible. Greenhouse plants benefit from good ventilation, and gently tapping flower trusses can help move the pollen around.

Finally, don't panic about every curled leaf. Tomato plants are surprisingly good at looking slightly unhappy when they're hot, recently pruned or growing vigorously. Look at the whole plant before reaching for a remedy. If it's green, growing and setting fruit, it's probably doing all right.