How to Grow Tomatoes

Gardening chat about growing your own veg often turns to the wonders of home-grown potatoes and tomatoes, but the two are very different crops to grow. Potatoes are much easier, and need little attention, (see growing potatoes.) Tomatoes are the opposite; time-consuming and more difficult.  When growing Tomatoes they need a lot of attention during the growing season starting with potting on, removing side shoots, thinning out the leaves as the plant matures, and as the fruits form, regular feeding and watering. All the effort is worth-while come harvest when it is so rewarding to pick fresh sweet tomatoes straight from the vine and eat them. For me, summer is the smell of tomato vines.

 Tomatoes are an ideal container crop the only drawback is that Tomatoes grown in containers are more prone to drying out during dry spells. If you are planning on growing tomatoes you will need to work out how to keep them watered during holidays. It is very disappointing returning from a lovely holiday to find your tomatoes plants suffering from drought. In the summer, if it is warm, tomatoes need watering several times in a week and if hot, daily attention. A gardening friend or neighbour is good, also there are also some effective irrigation kits on the market.   

    When growing tomatoes outside you need a warm, sheltered spot and if you don't have this in your garden Tomatoes are best grown in a greenhouse. In the growing guide below are helpful tips to ensure you have a successful, tasty crop of tomatoes. Tomatoes are not frost hardy so if you intend to grow tomatoes outside, only plant out when all risk of frost has passed. As a rule of thumb in the UK last frost will usually be at the end of May/first week of June. Even thought plants are sold in the garden centres from Feb - May do not plant out, treat them like a bedding plant and wait until the conditions are warm. Tomatoes grown under glass will fruit earlier and be less prone to blight.

Whether growing from seed or small plants, the first decision is what type of tomato to grow. The main choice is between bush type tomatoes which are, as the name suggests, bushy and suitable for hanging baskets and are generally easier to grow compared with Upright, or Cordon tomatoes. Upright tomatoes need more attention and check out the pros and cons of both types of tomatoes.

The advice below applies to growing all types of tomatoes, whether bush or upright. For advice on the extra steps needed for growing upright tomatoes.

See also: Common problems and diseases when growing tomatoes and How to grow Upright (Cordon/In determinate tomatoes)

10 top tips on How to to grow tomatoes

There is more information about all these tips below;  here is a quick guide checklist:-

  1. Grow a variety of tomato most suited to your growing conditions. For example, if growing tomatoes outdoors pick a variety which is blight resistant, beefsteak tomatoes take need a lot of sun and light whereas smaller cherry tomatoes will ripen sooner if you want an earlier crop. 
  2. Pot on 2/3 times during the growing season.
  3. Harden off before planting outside
  4. Most, most, most important feed and water regularly. 
  5. For upright tomatoes, these are tomatoes with one single stem as compared to bush tomatoes and are also known as  Cordon tomatoes,  remove the side shoots to ensure there is just one central branch.
  6. For upright tomatoes thin foliage throughout the season or the plant will be all leaf and less fruit.
  7. Start feeding when the flowers appear
  8. Once the plant has 3 sets of flowers stop off the top growth.
  9. Stake and tie the plant to support it especially the fruit
  10. At the end of the growing season cut off vines and bring indoors to ripen.

How to Grow Tomatoes From Seed

small tomato plants

The growing season for tomatoes varies a little depending on where in the UK you are growing your crop. The season is longer in the country's south, where you can often germinate from seed as early as late February, with good light conditions and grow through until around late October/early November. Tomatoes need good light and heat to grow well. If your garden is not sheltered it is best to start tomatoes off indoors.    

Tomatoes are easy to get started from seed. Place two or three seeds into a small pot filled with fine compost, cover the seeds with a light sprinkling of compost and they will germinate quickly provided they are kept warm and covered (with polyethylene or propagator) until they have germinated. Tomatoes need a temperature of around 21 C to germinate.

Early in the year when conditions are cool, it is best to germinate in a propagator to create a warm, moist atmosphere. The seedlings will emerge after a few days and once the seedlings emerge, uncover and reduce heat. If seedlings (of any plants, not just tomatoes, ) are left too long in a propagator the warm moist atmosphere will make the seedlings floppy. It is important as soon as the seedling has fully emerged to remove the pot from the propagator, and keep frost-free.

When deciding a variety of tomatoes to grow from seed, think about the size of the tomato. The large beefsteak varieties will need a longer, sunnier growing season to ripen than the smaller cherry type. This means where in the country you are gardening may be an important factor in deciding which type of tomato to grow. This is particularly true if growing tomatoes outside as opposed to in a greenhouse which provides a more sheltered growing environment.

As with all plants grown from seed, they can become leggy if light levels are poor. This is because the seedlings stretch towards the light, and if the seedlings are in grown in conditions where the light is uneven, or low light conditions, it will produce poor seedlings for potting on. Early in the year tomatoes grown inside, and in particular on a windowsill, can easily become leggy. If you do grow on a window sill where the light is predominately from one direction, turn the plant regularly. If the seedling turns out leggy, don't throw it away, but when potting on plant it deeper to overcome the problem. 

Tomatoes seeded in early spring will come to fruit later in the summer, depending on the weather conditions  and will produce fruit from late July onwards.  By November the plants will be finished, and can be thrown away or composted. In our climate tomatoes are an annual plant growing for just one season.

Video advice and tips on successful germination from seed.

Potting On Tomatoes

tomatoes in grow bag

When growing tomatoes as the plant matures, it will need to be " potted on" which means repotting into a larger pot. In the growing season, you may need to do this about 3 times from the small plug plant stage, until the tomato plant reaches a good which is large enough to go into full size pot or grow bag. 

It may be tempting to save time and put the tomato into a larger pot at the beginning, but this not ideal.  If you put a small plant into a large pot or grow bag, it will not thrive. Pot the tomato plant into a slightly larger pot doing this 2/3 times until planted into its final large growing container. 

It is a good idea to plant tomatoes deep, especially if your seedling is a bit on the weedy side. The only exception is in respect of grafted plants.  The last pot into which you plant your tomatoes as the growing medium for the rest of the summer, should have a diameter of between 20- 30 cms, and the larger the better. If you are growing a grafted tomato plant it is important to ensure when re-potting that graft union is above of the soil. 

Grow bags are often promoted as a good growing medium for tomatoes. Whilst they are convenient, the problem is the depth of compost is shallow which is not ideal. In addition, this can causes problems when watering as the water has a tendency to run off. The bag flatten increasing the difficulty in watering. For tomatoes, regular watering is absolutely essential and irregular watering impairs the flavour and can cause the skins to split later in the season. It is important to get the water to the plants roots. To increase the soil depth which will help with the watering problem, use tape to strap up the bag, or supports as in the image right, to make the bag more rounded. You need to get the plants to a reasonable size before putting into a grow bag as in the image. 

You can grow tomatoes in a greenhouse or outside,  but tomatoes do need a warm, sunny sheltered spot and not all gardens or parts of the country enjoy these conditions. An alternative is to grow in a greenhouse or poly tunnel which creates an ideal growing environment for tomatoes, and offers protection from blight.  Blight can be a real problem but is a rare visitor on greenhouse-grown tomatoes. If planting outside pick the most sheltered spot in your garden such as sheltered sunny patio.

When potting on a tomato plant is a good time to add a water bottle for effective watering, see below.

Short video showing how to pot on tomatoes 

Hardening off Tomatoes

tomato ties too tight

  If you are intending to grow your tomatoes outside, you will need to "harden off" the plants before planting them outside. This means getting the plants used to the cooler, less clement conditions outside, as opposed to controlled conditions in a greenhouse, lean to or indoors where the seedlings have previously grown. If you intend to grow outside, in late spring you will need to place the plants outside, starting on days when the weather is at its best placing the plants outside for increasingly longer periods. Only leave outside overnight once the risk of frost has passed. 

 Upright tomato plants get quite large, around 1.5 m (5 ft+ ) so they need plenty of support, especially later in the season when the branches are heavy with fruit and can easily snap. All upright tomatoes need to be tied to canes to support the plant and the fruit. The image left illustrates the wrong way to tie in a tomato plant. When the tie was put on, it probably looked Ok but as the plant has grown, the tie has tightened and damaged the stem. To avoid this use soft ties, check regularly and loosen as the plant grows. I like raffia as a plant tie, it's very strong and looks natural.   

Temperature wise tomatoes are less than happy below 15 C at night, and below 10 C could damage the plant. If the weather turns unexpectedly cold, protect the plant with a fleece. Equally too hot and the plants are not happy, ideally not above 35 C. This means on very warm days it is essential to ventilate the greenhouse and perhaps spray the floor with water if it is very hot to cool the greenhouse.  It follows from this that almost all conservatories in the summer months are too hot for growing tomatoes.

 It is essential for a good crop of sweet tomatoes to water and feed regularly, and this is true whatever type of tomato you are growing. All types of tomato plants need watering regularly, and it should be  increased the tomatoes fruits form and get larger. If you are growing tomatoes under glass or in a greenhouse, the tomatoes will need watering daily on warm days to make sure plants do not dry out. If the plant dries out this can cause the fruit to have tough split skins, and a less sweet flavour. One aim of growing your own tomatoes is to have sweet tasting fruit; irregular watering will impair the flavour. Regular feeding is equally important and feed with proprietary tomato feed as soon as the first flowers appear, and feed regularly throughout growing season. The bottle will give instructions to ensure the correct amount of feed to water ratio. 

The image left shows how not to water a tomato plant. It is important to try and avoid splashing feed or water the leaves which can raise the chances of disease.

The image right shows an effective way to ensure the water goes to the tomato roots. Cut the bottom off a plastic water bottle and sink it into the pot when you are potting on the tomato. This enables you to funnel the water down to the roots away from the leaves.

How often  should you water tomatoes? There is no rule of thumb, plants need less water when they are small so as the plant grows water more regularly. Do not let the compost dry out and the warmer it is the more water the plants need.

A foolproof way to ripen tomatoes

how to ripen tomatoes

  There is a perception that tomatoes can be difficult to ripen once the main summer is past. Often in October as the nights are drawing in the light levels are dropping, the plant is slowing down, and the fruit doesn't seem to ripen. The tomato plants still have loads of green tomatoes and chutney isn't the solution. 

When it's turning chilly, depending on Autumn weather, cut the tomatoes off the plant on the vine and lay them on cardboard/newspaper in a spare room, conservatory or in a dish on a sunny windowsill and they will ripen. The Sunday Gardener has used this simple method to ripen tomatoes for several years without fail. The vines need to be somewhere warm, and the fruit will ripen.

I found this method to work well when one year moving house in early Autumn. It was not practical to move the tomato plants and take them to the new house and so the only thing to be done was to cut all tomato plants down. The trusses of fruit were cut and left on cardboard in a warm place, and 80%+ ripened

last updated 12.05.2020