The ultimate guide to growing tomatoes

Tomato 'Alicante' from Thompson & Morgan

Tomatoes are an easy, satisfying crop
Image: Tomato 'Alicante' from Thompson & Morgan

You can't beat the taste of sun-warmed tomatoes straight from the vine - and they're so easy to sow and grow! Growing your own allows you to enjoy special varieties that can’t be bought in a supermarket. That’s because commercial growers need to focus on the disease-resitant cultivars that provide high yields. At home, your tomato crop can be chosen for scent, flavour, size, texture, colour and even lycopene levels. Here are some top tips on how to grow terrific tomatoes. 

Browse our full range of tomato seeds or choose tomato plants for a shortcut to success. 

How do you sow tomato seeds?

Check out this video for a step-by-step guide to sowing tomato seeds

Sow your tomato seeds in March or April, approximately 6-8 weeks before the final frost, or earlier if you're growing your tomatoes in a greenhouse. 

  • Sprinkle the seed thinly onto good quality seed compost. 
  • Cover with 1.5mm of compost and water lightly with a fine-rose watering can.
  • Keep the compost moist, but be careful not to over-water as wet conditions can encourage ‘damping-off’ disease, and other mould problems. 
  • Tomato seeds usually germinate in 7 to 14 days if you maintain a steady temperature of 21 degrees celsius. 
  • Pot on the tomato seedlings as soon as they're big enough to handle. 
  • Hold the plants by the leaves, taking care not to touch the stems, and transplant them into 7.5cm (3in) pots. Protect the plants from frost, cold winds, and draughts which might kill them.
  • If you're only growing a few plants, simply sow two seeds into a couple of 7.5cm (3") pots and remove the smaller plants as they begin to grow. 

How do you grow tomato plug plants?

Watch this video for a step-by-step guide to growing tomatoes from plug plants

Tomato plug plants are a great way to save time and space. Here’s how to get the most from them:

  • When your tomato plugs arrive, remove from the packaging as soon as possible and give them a good watering. 
  • Your plugs will have strong root systems, but they’re still too small to go outdoors or into a full size pot just yet. 
  • Pot up your plugs into 9cm pots using good quality peat free multi-purpose compost, handling the root ball to guide them in. 
  • Plant the plug deeply, up to the juncture of the first two true leaves and the stem. 
  • Firm the soil around the base of the plug gently with your fingers.
  • Water your pots well to settle the compost snugly around the roots. 
  • Leave your plugs for a few weeks in these pots in a warm sunny spot, keeping the soil moist. 

What variety of tomato should you choose?

Cherry Tomatoes Plum Tomatoes Heirloom Tomatoes Medium ('Normal') Tomatoes Beefsteak Tomato
Tomato 'Gardener's Delight' Tomato 'Crimson Plum' Tomato 'Ananas' Tomato 'Tigerella' Tomato 'Super Marmande'
Tomato 'Gartenperle' Tomato 'Aviditas' Tomato 'Craigella' Tomato 'Cristal' Tomato 'Gigantomo'® F1 Hybrid
Tomato 'Sweet Aperitif' Tomato 'Shimmer' F1 Hybrid Tomato 'San Marzano' Tomato 'Moneymaker' Tomato 'Gourmandia'
Tomato 'Losetto' Tomato 'Principe Borghese' Tomato 'Bellandine' Tomato 'Orkado' Tomato 'Buffalo Steak'
Tomato 'Suncherry Premium' Tomato 'Nagina' Tomato 'Buffalosun' Tomato 'Alicante' Tomato 'Crimson Blush'

If you're still undecided, take a look at our comprehensive tomato selector guide to help you choose which varieties to grow.

How do you grow tomatoes in a greenhouse?

Slowly ripening tomato 'Sungold' variety on stem

Varieties like 'Sungold' thrive in greenhouses
Image: Tomato 'Sungold' from Thompson & Morgan

Growing tomatoes under glass produces an early crop, especially if you choose recommended varieties like 'Sungold', the quick-maturing 'Shirley' or the beefsteak 'Country Taste'. Here are some tips for greenhouse growing:

  • Sow your tomato seeds in 7.5cm (3") pots from February onwards, according to the instructions on the seed packet.
  • Plant your young plants when they’re about 15-20cm (6-8in) tall and the flowers of the first truss are just beginning to open. 
  • If you're growing in a greenhouse border, make sure you dig in plenty of garden compost or well-rotted manure during the winter, and do remember to rake in a general purpose fertiliser before planting.
  • If you've used your borders for tomatoes before, change the soil before growing them again or soil pests and root diseases can be a problem. 
  • Growing tomatoes in pots or a grow bag? Remember they'll need a lot more water and care.
  • Plant your tomatoes about 45cm (18in) apart, leaving 75cm (30in) between rows, and if you're planting into a grow bag, limit yourself to two plants per bag. 
  • Tomatoes prefer a temperature of 21 - 24C (70 - 75F) and will perform poorly at temperatures above 27C (81F) or below 16C (61F). 
  • Make sure you ventilate the greenhouse regularly to deter pests and diseases.

How do you grow tomatoes outside?

Cluster of tomatoes on stem with green tomato on lower level

If you don’t have a greenhouse, use tomatoes that are known to flourish outdoors, like 'Moneymaker'
Image: Tomato ‘Moneymaker’ from Thompson & Morgan

For the best results, choose trusted favourites like 'Moneymaker', 'Gardener's Delight', or 'Alicante' that are all known to do well outside. Alternatively, if you're growing your tomatoes in hanging baskets, go for trailing varieties like 'Tumbling Tom Red' or 'Tumbling Bella'. Here are some tips for outdoor growing: 

  • Wait until approximately 6-8 weeks before the last frost is forecast and sow as directed on the seed packet in 7.5cm (3in) pots. 
  • Plant out the young vines when they're about 15-20cm (6-8in) tall, the flowers of the first truss are just beginning to open, and the risk of frost has passed.
  • If you're planting into the ground, make sure you dig in plenty of garden compost or manure during the winter, and just before planting, rake in a general purpose fertiliser. Tomatoes are hungry plants!
  • Plant your tomatoes about 45cm (18 in) apart, leaving 75cm (30in) between the rows. 
  • If you're using grow bags, limit the number of plants to two, and do remember they'll need extra watering and care.
  • To save space, try growing your outdoor tomatoes in hanging baskets, or upside down. Simply plant a young tomato plant through a hole in the bottom of a bucket or similar hanging container, and fill the container with multi-purpose compost. Suspend the bucket from a bracket and allow the plant to dangle beneath it.

How do you train tomato plants?

Two groups of tomatoes supported by ties

To ensure healthy tomato growth, training them to rely on a support is crucial
Image: Tomato 'Crimson Crush' (Grafted) from Thompson & Morgan

How you train your tomato vines depends on which varieties you’re growing.

  • Cordon/indeterminate: The most common tomatoes, these single-stemmed plants grow very tall, sometimes reaching 2.5m. You do need to provide support and remove the side shoots. 
  • Semi-determinate: Similar to indeterminate varieties (grown as cordons) but producing shorter plants.
  • Bush/determinate: These varieties stop growing sooner than cordons with the stem ending in a fruit truss. They’re referred to as 'bush' and 'dwarf' types, and are suitable for hanging baskets. They don't require any pruning.

With indeterminate and semi-determinate varieties (cordons), tie the plant to a support as it grows. Pinching out the side shoots as they develop concentrates the plant's energy into producing fruit. When the cordon reaches the top of its support, cut out the tip of the main stem two leaves above the top flower truss.

For the best quality fruit it's best to limit the number of fruit trusses to six per plant. If the vine doesn't reach the top of its support by late summer, cut out the main tip anyway to give the remaining fruits time to ripen.

Determinate varieties (bush/dwarf types) don't need pruning or training and happily sprawl along the ground or around the pot they're growing in. Determinate varieties can stop flower production after several trusses, but you can encourage continued upward growth by training up the topmost side shoot.

How much water do tomato plants need?

Watering tomato plants planted in ground

To produce a bountiful crop, tomatoes need regular and plentiful watering
Image: Fotokostic/Shutterstock

Tomato plants need a lot of water and feed if they're to produce a bountiful crop. For best results, water little and often. Some gardeners leave a few filled watering cans to warm in their greenhouse so the water is not shockingly cold from the tap or water butt. There are also those who claim that watering at exactly the same time each day makes a difference to the quality of the fruits. 

Feed your tomatoes with a general liquid feed until the first truss has formed then alternate with a high potash feed to encourage more flowers and fruit.

When should you harvest tomatoes?

Ripe beefsteak tomatoes in basket

Harvest tomatoes as they become ripe
Image: Tomato 'Buffalo Steak' Grafted from Thompson & Morgan

Start picking your tomatoes as the fruits ripen and gain full colour. When frost threatens at the end of the season, lift any plants with unripe fruit on them and hang them upside down under cover. Tomatoes can be successfully frozen if you find you have a glut.

Common problems with tomato plants

Four blight-stricken tomatoes on diseased plant

Like potatoes, tomatoes get blight. Make sure you take the right precautions when growing
Image: Radovan1/Shutterstock

Tomatoes can succumb to several problems, but many of these are caused by growing conditions that can be easily avoided with a little know-how. Be sure that your plants receive the correct amount of warmth, light and water, being careful not to splash the leaves as you water. Here are some of the most common problems and how they can be avoided: 

Tomato blight

A common problem caused by wet weather, particularly with outdoor plants, tomato blight spreads fast, leaving telltale brown patches all over the plant. Not only does blight kill vines, it also rots the fruit. How to stop blight? Grow blight resistant tomato varieties or spray Bordeaux Mixture on your plants early in the summer.

Fruit problems

Irregular watering, or too much water too late in the growth cycle causes fruiting problems like:

    • Blossom End Rot: Dark patch at the base of the fruit, more common if the plant is grown in a grow bag.
    • Blossom Drop: Flower bud falls off.
    • Dry Set: Fruitlet growth stops when the fruit is the size of a match head.
    • Splitting fruit: Large fissures open up on the fruits as they grow.

    The key to a healthy crop of tomatoes is regular, even watering, delivered to the base of the plant. Too much water too late tends to be the problem in most cases, especially with plants grown in pots and grow bags.

    Too much direct sunlight can also damage your crop. Tomatoes need high light intensity to grow well, but too much can cause blotches, scalds or spots on the developing fruit. 'Greenback' is a common problem caused by too much sunlight, leaving the ripe fruit with a hard green area on its 'shoulder'.

    If this is a problem, increase the potassium in your plants' feeding regime and use fleece or shading as a cover in the hottest part of the day. It may also help to use resistant varieties like 'Alicante' or 'Craigella'.

    Insect pests

    Keep a keen eye out for green and white fly because both can spread viruses. Spray your vines with a recommended insecticide as soon as you notice pests. Organic gardeners might prefer to sow marigold seeds nearby which attract beneficial insects that eat pests.

    Leaf problems

    • Curling leaves: May be caused by aphids sucking the sap from them, but if there's no sign of insects the most likely culprit is cold night-time temperatures (more noticeable in early summer). If this is the case, it's nothing to worry about. Learn more about tomato leaf curl here. 
    • Mosaic patterns, streaks or distorted leaf surfaces: Your tomatoes may have a virus, in which case your best bet is to remove and destroy them before the problem spreads. Always disinfect tools, boots, and gloves after handling diseased plants. 
    • Leaf yellowing starting on older leaves and moving upwards: The problem could be a magnesium deficiency which is easy to remedy with a special magnesium feed.

    Growing tomatoes is such a satisfying way to add homegrown flavour to soups, salads, sandwiches and more. For everything you need to know about growing tomatoes, visit our dedicated hub page.

Sue Sanderson T&M horticulturalist

Written by: Sue Sanderson

Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman's nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.

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