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OUTDOOR TOMATOES IN THE UK


This article contains all the information an amateur gardener needs to grow top quality tomatoes outdoors in the UK. The unique calendar below can be personalised to the weather conditions in your area of the country (click here to do that now). The default setting will be average UK weather conditions.

TYPES OF TOMATO PLANTS FOR PRUNING

There are two types of tomato plants as far as pruning is concerned, in all other respects both types can be treated the same when growing tomatoes outdoors.

BUSH TYPES
These types require no essential pruning other than removing dead or decaying foliage. They naturally reach a certain height and width, then stop growing.

CORDON TYPES
This type will continue growing upwards and outwards and needs to have some basic pruning performed on them when side shoots appear. This is explained in detail, with pictures, later in this article.

If you aren't sure what type your variety is, first consult the seed packet which should give you this information. If you are still not sure than click here to go to our tomato varieties page for this information.

For all the tomato varieties which we have fully reviewed, click the drop down box below, select a variety and then click the More Information Button.


 

QUICK CALENDAR FOR OUTDOOR TOMATOES


  • Sow seeds in pots indoors
    Second week of March 2017
  • Pot up young plants
    Second week of April 2017
  • Harden off young plants
    First week of May 2017
  • Plant out young plants
    Third week of May 2017
  • Begin high potash feed
    When flowers die off
  • Begin pruning cordon type
    When side shoots appear
  • Begin harvesting tomatoes
    First week of August 2017
  • Begin nitrogen feed
    First week of September

WHERE TO GROW OUTDOOR TOMATOES


There are two main methods for growing tomatoes outside in the UK, in grow bags / large containers or in the open ground. From our experience we know that most gardeners grow their outdoor tomatoes in grow bags and containers although we have seen several gardeners grow large amounts of tomato plants on allotments in open ground.

The advantages of growing tomato plants in grow bags and containers are summarised as:

  • The soil conditions in the grow bag are ideal
     

  • No digging is required
     

  • The grow bags can be positioned for maximum sun exposure and wind protection
     

  • Feeding is more easily controlled
     

  • Small portions of land can be used which might otherwise go to waste

The advantages of growing outdoor tomatoes in open land can be summarised as:

  • No purchase of grow bags/ containers needed
     

  • Larger numbers of plants can be more easily and economically grown
     

  • Adequate and consistent watering is far, far, easier
     

  • More trace elements are normally available to the plants in open ground and this leads to better tasting tomatoes

Whichever method is chosen, tomatoes benefit from as much sun as they can possibly receive in the UK. Tomatoes will grow in partial shade although they will produce less of a crop and it will be later in the year. Tomato plants also prefer positions protected from winds.

If you are growing tomato plants in open ground, dig the soil well and add lots of well-rotted organic matter. You are aiming for a free-draining but water retentive soil. A couple of weeks before planting out your tomatoes sprinkle a good handful of blood, fish and bone per square metre (yard) over the soil surface and gently work it in with a rake, hoe or similar.

Grow bags and multi-purpose compost should have sufficient nutrients already in the compost to feed your tomato plants for four weeks. Always use fresh compost bought in the current year, old compost and grow bags used last year will have pests and diseases in them which will almost certainly do damage to tomato plants if used again.

Containers and grow bags must have drainage holes in the bottom and this is often not the case. Check for drainage holes well before planting because it is very difficult to add them later on.

SOWING OUTDOOR TOMATOES



TEMPERATURES FOR SUCCESSFUL TOMATO SEED GERMINATION


Some basic rules need to be followed when sowing seeds. First, tomato seeds require a soil temperature of at least 10°C / 50°F to germinate and above 35°C / 95°F they will fail to germinate. The best temperature range is between 18°C / 64°F and 22°C / 72°F.

A small fall in the temperature at night time is perfectly acceptable although the more even the temperature the quicker the seeds will germinate. In the UK it's almost impossible to achieve the optimum soil temperatures for germination early in the season wherever you live, so we strongly recommend sowing and growing on the seedlings indoors.
 


HOW AND WHEN TO SOW TOMATO SEEDS


It's important to get the timing of sowing tomato seeds correct because you can sow them too late and end up with a late crop, or, you can sow them too early and end up with a houseful of large, light-starved plants just waiting for the last frost before you can plant them out. 

We recommend sowing tomato seeds in 7cm / 3in pots initially, anything smaller and you will need to pot up (transfer the seedling to a larger pot) more frequently with no benefit.

The best time to sow tomato seed in average UK areas is the second week of March 2015. Click here to personalise dates in the site to your town.

Fill the pots nearly to the top with multi-purpose compost, place one or two seeds (depending on how expensive they are) on the compost surface and then lightly sprinkle a centimetre more compost over the seeds. Gently pat the compost down over the seeds and water, preferably by placing the pots in 3cm / 1 in of water until it is damp through. Place the pots in a warmish area of the house (18°C / 64°F and 22°C / 72°F), with or without light, it doesn't matter at this stage.

The seeds will take one to two weeks until they germinate and a seedling appears. As soon as that happens move the pots to a light and airy position such as a windowsill but not in direct sunlight. At this stage aim to grow them on in a temperature of around 18°C / 64°F - small differences in the temperature are not a problem. However, as always with growing plants on a windowsill, be aware that occasionally night time temperatures can get low and the plants will not withstand much lower than 6°C / 43°F without ill effects and a frost will kill them them stone dead.

Tomato seedling

If you are growing on a windowsill where the light only comes from one direction you will find that the plant bends towards the light. To even the plant's growth up turn the pot halfway round every day or so.

If you want to know how to save tomato seeds, our seven step guide with pictures is ideal. It's easy to do, costs nothing and above all it's fun and environmentally friendly. Click here to go to the page.

POTTING UP TOMATO PLANTS


Roughly four weeks after sowing tomato seed in 7cm / 3in pots the plants will need to be transferred to a larger pot to allow more room for the roots to grow. If you follow our advice on the timing of sowing seed we recommend potting up the plants into 12cm / 5in pots although a centimetre or two more will be fine. To judge when to pot up tomato plants, they should be about 10cm / tall. More importantly, the roots should have reached the base of the existing pot, see the picture below.

Tomato plant ready for potting into larger pot

Roots have reached the base of the pot

Turn the plant and soil out of the old pot into the palm of your hand. Carefully place it centrally into the new pot, do not add any compost to the base of the larger pot before doing this.

Ready for potting up

Tomato plant prior to potting up

Now infill the space in the new pot with more compost, gently firming it down as you go. If you follow these instructions on potting up you will find that the tomato plant is slightly deeper in the compost compared to before and this is ideal. This will allow the stem to sprout new roots higher up the stem and ...... more roots mean more tomatoes at harvest time! The same principle will apply when you plant the tomatoes into their final positions.

Tomato plant after potting up

Tomato after potting up (click to enlarge pic)

The new compost will provide enough nutrients for the next three weeks but after that feed them with a balanced liquid fertiliser once a week at the rate recommended on the packet / container. Keep turning the pot around to ensure light reaches all sides of the plant and it grows upright rather than towards the light.

Tomato plants and seeds for sale

HARDEN OFF TOMATO PLANTS


A week or two before planting out your tomatoes you will need to acclimatise them to outside temperatures and weather conditions, this process is called hardening off. Start this off during the first week of May 2017 by placing the plants in a protected position outside during the day for a couple of hours at first. Day by day increase the amount of time they spend outside by an hour each day. Always bring them inside if a late frost threatens.

YELLOW LOWER LEAVES ON TOMATO PLANTS


When tomato seedlings first grow they have two leaves (called cotyledons), see the picture above here. These leaves are specially designed to protect the growing tip as the plant pushes to the surface. When they reach the surface and sense light the plant immediately begins to produce normal leaves which are designed to convert light into energy and enable the plant to grow a root and canopy system.

Yellowing lower leaves on a tomato plant 

As the plants grow and develop true leaves the seedling leaves have no purpose any more so they turn yellow and eventually fall off of their own accord. You can of course gently pull them off as soon as true leaves develop.

The point being made is that yellowing seedling leaves are completely natural and nothing to be concerned about.

If more lower leaves start to turn yellow then that is a concern. The normal reason for yellowing leaves on tomato plants is that there is a shortage of nitrogen. To correct add a balanced general purpose liquid fertiliser to the water when you water the plant. The frequency and amount are as stated on the packaging.

Another reason for yellowing leaves is that the plant is simply too big for the pot and needs to be potted up. If a large plant is grown in a small pot the roots are not able to absorb sufficient nutrients to support the above ground growth and the leaves may start to turn yellow.

Another possible reason for yellow tomato leaves is that the compost is water-logged. This also stops the roots absorbing nutrients and causes yellow leaves. The solution is to stop watering for a short period of time.

PLANTING OUT TOMATOES


Only plant out your tomatoes when all danger of frost has passed, in average UK areas this is the third week of May 2015. Click here to personalise dates in the site to your town. If you are planting them directly into open ground prepare the soil by digging it to a fine tilth to a spade's depth. Sprinkle a handful of blood, fish and bone per square metre / yard onto the planting area and work it into the soil surface.

Tomato plants prefer a soil which is slightly acidic although they will grow successfully in most garden soils. The ideal pH would be in the range 6.0 to 6.8. A neutral soil has a pH of 7.0. Click here to learn more about soil pH levels.

The procedure for planting is the same for grow bags and in open soil. Use a trowel to dig a hole slightly wider than the pot and about 5cm / 2in deeper. Place the plant in the hole and infill with the surrounding soil / compost gently firming it down as you go. The plant will end up 5cm / 2in deeper below the soil surface than before allowing the newly buried part of the stem to sprout more roots as the plant grows. Water in well to settle the soil around the roots and also provide initial moisture.
 

One good idea for planting out tomato plants in grow bags, pots and in open soil is to use a bottomless container filled with compost. The picture below (click it to enlarge and see more clearly) shows a bottomless pot (we simply cut the base off with a sharp knife) filled with multi-purpose compost. The pot is placed over prepared open soil but can just as easily be placed into a hole cut into the top of a grow bag.

When planting in open soil this gives the young tomato plant an ideal soil into which it can initially establish itself. When the roots reach the base of the pot they will grow easily into the normal soil.

Tomato plant in bottomless container

The benefits for using the same system with grow bags is that the tomato plants have a larger area to spread their roots and absorb nutrients, it also reduces the need for frequent watering.

Allowing enough space between plants is important to permit good airflow and reduce the risk of fungal diseases such as blight. The space depends to a great degree on which variety of tomato plant is grow so follow the instructions on the back of the packet of seeds. A spacing of 45cm to 60cm (18in to 24in) between plants should be fine in most cases.

Cordon tomato plants will need support during the growing season. Where they are grown in open ground a single stick can be inserted into the soil near the plant. Allow for 1.2m above ground and about 50cm below ground. Tie the main stem into the support as it grows. The same can be done for plants grown in grow bags although commonly the are grown against a fence which can sometimes be used to provide support.

COMMENTS / QUESTIONS LEFT BY OUR READERS

Date: 19 April 2017 From: Grant
QUESTION: Following your excellent, clear instructions, my tomato seedlings (moneymaker, gardener's delight and losetto) are now enormous, 12-16 inches! I think this is because they have been grown on a warm, very light windowsill. Some of them are flowering now (intending to pinch those out) so I'm very keen to get them planted out following your schedule for my area in the first week of May, and I am hardening them off at the moment. My question is, what day and night temperature range will they tolerate/thrive in? I'm worried that it's not going to be warm enough for them to harden off over night in time to hit the 1st wk May planting out target.
 
ANSWER: My routine for hardening off tomato plants is to put them out at day time (bringing them in at night) for a week and then also against a house wall at night for another week.

You know your own climate better than anyone else, and there has just been a few nights of slightly colder night temperatures compared to normal. I would think that a temperature below 7C begins to cause a problem for tomato plants especially if it occurs two or three nights in a row. 4C or below and the risk of damage is significant.

On those figures, I look at the 7 day weather forecast (the Met Office forecast not the BBC or others) on the day I plan to plant them out and take it from there. At this time of year the temperatures can increase quite quickly even over a week.

If space really does become a major problem and the weather just simply isn't acting according to plan, I have been known to move half of my plants off the windowsills and onto the floor of the coolest room of the house. Next day I swap them round. Not ideal I know, but it buys an extra week without any major problems. A week at this time of year a week can make all the difference.
 

Date: 15 April 2017 From: Elizabeth
QUESTION: April 2017 as a novice grower. Wondering why my tomato plants, which are 12 inches high, have flowers on them. They have been in my conservatory.
 
ANSWER: Some tomato plants flower early, some flower late. Growing conditions also influnce when flowers are produced.

You are growing your tomatoes in a conservatory which is probably warm so the plants think summer has arrived.

Unless you live in the warmest areas of the UK, my advice at this time of year would be to pinch off (prune off) the flowers and let the plant put all its energy into growing roots and foliage for the moment. It will produce more flowers in a few weeks and these can remain.

Date: 18 March 2017 From: Brian S
QUESTION: Billingham In the Northeast the climate is generallu colder than the South. When (roughly) is the earliest I can plant well established tomato plants in a small greenhouse? I appreciate that temp. is important. My plants are ready now to plant to a permanent site (greenhouse, unheated) and I was hoping to do this in the middle of March. You advice would be appreciated
 
ANSWER: It all depends on how much risk you want to take. Billingham in Durham is indeed in a cooler part of the UK. The last frost is normally around late April but most gardeners would not plant out tender plants until mid to late May in your area of the UK. Frost damages tomato plants considerably and in many cases will kill them.

Your unheated green house will give some protection againsta frost but not much - maybe shifting the dates by a week or two. With those comments you can decide if the middle of March is a risk worth taking. I certainly wouldn't take the risk.

Date: 21 July 2015 From: J Blackmore
QUESTION: I'm a bit of a novice a growing, I bought some easy to grow tomato seeds and it said on there I could put in propagator in from Feb onwards which I did, they are now 3 inches high and wanted to know if I should put them in bigger pots outside in my greenhouse
 
ANSWER: Always question what they say on the on the seed packet! Always double check it out.

First, assuming you live in an average UK temperature area (there are significant differences in temperature in the UK), I would suggest sowing tomato seeds in the second week of March, aound now.

The problem with sowing tomato seeds earlier is that the plants cannot stand any frost damage. An unheated greenhouse provides only minimal protection against frost. So I would suggest that the plants are only safe in the greernhouse from mid April. Prior to that the plants need to be kept in a frost free place with lots of light.

You say you are a novice, so you will soon find out how much room your current tomato plants take up - by the beginning of April they will will have grown significantly.

As far as potting up the plants is concerned, that depends on what size of pot they are in now. As a general rule of thumb, they will need potting up when the height or width of the plant is twice the width of the pot.

Date: 21 July 2015 From: J Blackmore
QUESTION: A lot of the tomatoes are very small like marbles also the leaves look very tired have been growing in a large window box filled with garden soil for last 3 years, should i change soil?
 
ANSWER: Yes, change it for good quality multi-purpose compost. Garden soil is not the best for growing tomatoes in containers, multi-purpose compost gives far better results.