How To Grow Tomatoes in The UK

How To Grow Tomatoes Is The Most Common Question I’m Asked As a Retired Commercial Tomato Grower. Here Are A Few Tips That Will Help You Grow Superb Tomatoes.

Tomatoes are widely grown and one of the most researched food crops on the planet. So there is a lot of expertise available. However, new and established amateur tomato growers often struggle with toms as how to grow tomatoes isn’t always obvious.

In this article, I’m going to cover the different sorts of tomato, how to propagate tomatoes, how and where to grow them, the best cultural methods, how to feed and water them, how to maximise fruit yields, the pros and cons of grafted tomato plants, tomato blight and when its best to pick toms.

The Origins Of Tomatoes in the UK

British gardeners haven’t always grown tomatoes. The plant isn’t indigenous, it comes from the Andes of Peru, Chile, Bolivia and Colombia.  In its natural state, the tomato is a plant with insignificant small green fruit, so different to what we grow today.  But it’s a crop of great genetic diversity and even now geneticists look to the original species to find desirable traits to breed into modern varieties. The original species all have small green inedible fruit, so it’s quite amazing that mankind has bred such a diversity of cultivars from such an unpromising starting point.

Tomatoes are normally diploid, though a few tetraploid varieties have been produced.

Tomatoes were first brought to the UK around 1590. Before that Hernan Cortes brought them to Europe and it’s possible Columbus brought them to Europe as early as 1493. They were recorded in Italy in 1548.

So in the UK, we were latecomers to tomato growing.  In fact, though they were here for many years they were considered poisonous and not consumed. In a sense that isn’t surprising as the tomato bears the Latin name Solanum lycopersicum and the solanums are the nightshade family.

However, one of the first mentions of tomatoes in the UK was by herbalist Gerard, in his Gerard’s Herbal published in 1597. But they weren’t grown for eating until the early 18th century when some of the gardeners in large country houses started to grow them. By the middle of the  18th century, the fruit was more widely consumed in soups, broths and as a garnish. It wasn’t however until the 1820s that the fruit was widely consumed by “the common people”.

How To Grow Tomatoes: The Different Types and Varieties

There was a time when tomato growing in the UK meant growing the traditional spherical/ round-shaped fruit

Today we have

• Conventional “Round” Tomatoes (often called vine tomatoes, though all tomatoes grow on a “vine”! This is the spherical tomato that grows around 8 fruit to the lb.).
• Plum Tomatoes (used for sauces and pastes, its widely grown outdoors in Italy for the canning/bottling/paste industry)
• Cherry Tomatoes (small and sweet, and if you get lots of sunshine and add potash they are even sweeter, mainly used in salads)
• Grape Tomatoes (like a cross between plum and cherry tomatoes, they are smaller than cherries and the skins are thicker)
• Campari Tomatoes (bigger than cherry, smaller than plum but very juicy and sweet)
• Tomberries (tiny variety about 5mm in diameter and I have to ask why would anyone bother with them?)
• Oxheart Tomatoes (a heritage variety that’s shaped like strawberries, big like beefsteak)
• Beefsteak (weighing up to a pound or two, with plenty of thick flesh they are often used for sandwiches).

There are now more than 10,000 tomato cultivars in existence. Some are listed here.

Choosing A Tomato Variety

Perhaps the hardest part of growing tomatoes is therefore choosing a variety. Personally, I like to grow something tried and tested. Commercially I tested hundreds of varieties but never found anything better than Moneymaker and Gardeners’ Delight. But I have to stress this was for my market. Neither gives the highest yield (which is what many commercial growers want, and these varieties don’t have the qualities that supermarkets want (such as the ability to be moved long distances by air/lorry or the shelf life they want).  But they do have good flavour and suit amateur conditions far better than many modern varieties which have been bred for commercial use with some being sold into the amateur market.

Determinate or Indeterminate Tomato Varieties

There are two main types of tomato and this often confuses people a lot. The difference is down to botanical properties which differentiate the way they grow. They are called determinant and indeterminate growth.

Simply put determinate toms grow to a certain height and no further. The upward growth is replaced by a truss of flowers and the plant just can’t get taller.  But all tomatoes produce side shoots (often mistakenly called suckers) which creates a bush-type growth and that’s what determinate toms do. Eventually, each of these sideshoots also terminates in a flower truss. But, it’s a bit like groundhog day, as each of the sideshoots also produces sideshoots and the bush gets denser and denser. The endpoint with this bush getting denser is that fruit is hard to see and pick and disease is encouraged.

Determinate, bush toms are fine in certain conditions, such as to grow toms that are used in canning or for paste. In this case, they are often machine picked rather than picked by people and it’s an example of highly intensive agricultural scale growing.

Indeterminate toms don’t end in a flower truss. They will form a bush if the side shoots are not removed. But if the sideshoots are removed they will grow to enormous lengths without the determinate flower truss stopping them. Commercially, the long season heated crops, grown in greenhouses, frequently grow 10 metre (30 foot) long “vines”.  To do this they are grown up long strings that are layered as they get to the tops of the string. The image shows a layered tomato crop and the railway tracks that are used to transport picked crops. The crop has just been de-leafed and the leaves are on the floor. they will need to be removed or will become a source of disease.

There is more on de-leafing and disease later in this article.

Sowing Tomato Seed

Tomatoes are normally grown from seed each year and this gives the gardener the choice of growing their own seed or buying plants from a garden centre. Plants can also be grown from cuttings but this is only done in rare cases. I’ve never seen it done commercially as there is a disease risk that just isn’t worth taking. However, some gardeners may choose to take cuttings from their first crop to grow a later crop. It is easy to do and the cuttings root very easily and quickly.

Seed can be bought from commercial seed companies or can be saved from a previous years crop. Some people prefer to take seed from shop-bought tomatoes and grow this. It germinates OK, but I don’t recommend it as there is no way of telling how good the plants and yields will be. Seed grown from shop bought toms that were grown overseas are unlikely to do as well in our climate and there is also no way of telling if the fruit is from the F1 variety .. in which case it is likely to be inferior due to Mendelian Inheritance issues.

Seed should be sown 5-6 mm deep in moist seed compost and ideally germinated at around 21C.  The seed will take around a week to germinate, though some varieties are slower or faster.

Once germinated the seedlings can be transplanted into pots or modules as soon as they show signs of the first new leaves. The actual stage at which they are moved isn’t critical but it’s better to go earlier rather than later to prevent the seedlings from getting crowded or short of nutrients.

Growing Tomato Seedlings to Planting Size

Tomatoes like it warm so they need to be grown on at around 21-25C. If it is cooler they will grow slower but will continue growing until it gets down to 16C or so after which the growth will significantly slow down.

The size at which they are put into their final growing position will vary depending on many factors. When I grew tomatoes commercially they would follow a crop of early spring lettuce. We aimed to start cutting lettuce on April 1st and needed to clear a whole greenhouse before preparing it for tomatoes. This took at least a week and we needed to keep the tomatoes growing well without getting checked before planting. In my case, I was cutting 30,000 lettuce and replacing them with 10,000 tomato plants so this was not something that could be done in an afternoon. It was always a bit of a juggling act!

Now that I grow a few tomatoes on an amateur basis I can just move my toms into bigger and bigger pots if I wish and plant much later.  It’s far more relaxed.

When transplanting tomatoes ensure you don’t handle them by the stem. If the stem gets damaged there is a high chance of fungal diseases entering via the wound and the plant could die. Handle the plant by the leaves. The plant should be planted as deep as possible but the cotyledons (seed leaves) should be above the compost soil surface. the same applies when planting in the final position. Don’t bury the seed leaves.

Some people use a cane to support the small tomato plants. I find it an unnecessary waste of time. A well-grown tomato plant will support itself until it is half a metre high. Canes just get in the way and being a pointed stick are a hazard to anyone bending over to inspect the crop.

Top Propagation Tip

Plants have an inbuilt wish to produce seeds. And a plant that thinks it’s going to die will do all it can to produce seed before it dies.  Lots of plants bolt due to poor growing conditions. And if you are after the root or stem of the plant that is a problem. But with tomatoes, it’s an advantage.  We are actually after the fruit that carries the seed. So a tomato plant that thinks it’s going to die is likely to work even harder to produce fruit.

But if we nudge the plant towards thinking the worse it is likely to produce more flowers and then more fruit. So the skilled tomato grower nudges the plant just enough.  The unskilled grower nudges the plant too far and the plant dies without fruiting.

So here’s my secret to nudging the plant just enough .. but not too far.

A week or so before planting gives the plant a thermal shock ie drop the night time temperature a bit. If you do this correctly the leaves will go a bit “blue” on the underside (we say blue but it’s more of a purplish colour).

Then when planted in the final position give the plant a good watering to encourage it to root out into the soil of compost and then leave it until it gets to the point of wilting. But BEWARE .. wilting can soon lead to dead plants! So only do this if you are confident you can do it properly.

Supporting The Growing Tomato Plant

Cordon grown tomato plants, the indeterminate ones that grow high into the greenhouse roof, need some form of support. Amateurs often use bamboo canes and tie the plant to them. To me, it’s a laborious process that wastes time and is expensive. I prefer to use a string that is suspended from the greenhouse or polytunnel roof.

In my greenhouses and tunnel, we had rows of wires running across the structure to which we attached tomato strings.  Each plant had a string and these could be tied to the plant or the method I preferred was to bury it under the plant. This is easy if the string is tied to the supporting wire and put under the plant as it was planted. We’d string a whole house before starting to plant. A strung house is a strange-looking sight. The greenhouse has been rotovated, the drip irrigation is in rows and thousands of strings hang above the irrigation pipes. It looks a bit like a spaghetti forest.

Once the plant starts to grow, rather than tie the plant to the string, we would twist the plant around the string, being careful not to trap the flower truss.  The video shows how this was done.

Feeding and Watering Tomatoes

Tomatoes are hungry plants. They need plenty of nutrition if we are to get the best yields and flavour. They also need sufficient water. I say sufficient as we can give them too much water as well as not enough. Judging the right amount isn’t easy for beginners (or even experienced tomato growers on occasion).

Let’s start with tomato feeding. Toms need a good supply of macronutrients: that’s nitrogen (N), potash (K) and phosphates (P). But give too much nitrogen and the plant diverts its growth into producing leaves rather than focusing on fruit. Potash is good for flowers and fruit PLUS flavour. So we need the right mix of nitrogen and potash. And that is exactly what tomato fertilisers are designed to give. They have the right balance of NPK in the correct plant food ratio. For example, Tomorite has a plant food ratio of 4-3-8.

The plant food ratio given will depend on the naturally occurring nutrient levels in your soil or compost. When I grew tomatoes commercially my phosphate levels were relatively high and I used a process called “flooding” to wash excess N & P out of the soil each year (in other words I put the irrigation on for 8-10 hours to wash excess N & P out of the soil.   This then gave me a known starting point that was low and I would also carry out a full soil analysis to ensure I then started with a fertiliser base dressing that was correct.

After that, I used a home mixed liquid fertiliser from when the first fruit were pea-sized. In my case, I used a base dressing of Vitax Q4 in the soil and fed with the liquid feed that was made from Potassium Nitrate which contains 13% N and 44% K. That’s a plant food ratio of 13:0:45 or roughly 1:0:3 .

How I Feed Tomatoes Today

Now I grow my toms in large containers that are needed in the soil so the roots can get into the soil below. To this, I add a good handful of Q4 and mix it thoroughly. I then use Tomorite mixed as per the instructions as a liquid feed. It’s a bit rough and ready as I appreciate that a handful is approx .. we all have different size hands. But, whereas when I grew commercially I operated to fine degrees and controlled nutrient levels, watering, humidity and temperature within fine tolerances, it’s not possible as an amateur. So we have to work to the rough and ready measures.

Though I follow the mixing instructions on the Tomorote bottle I do ignore one instruction. They say feed once a week. I feed EVERY day.

Why? Because of what I said earlier. Potash promotes flower and hence fruit growth, AND flavour. Tomato flavour depends on a complex mix of the right acidity and sugar levels. And potash boosts the combination and improves the flavour. The more potash we give the better the flavour .. of course, there’s an upper limit where too much potash kills the plant but we aren’t talking about giving that much!

Watering Tomatoes!

Advising on the amount of water is hard. So much depends on the weather, size of plant, temperature etc. On dull, wet cloudy days the plant is going to transpire much less than on a hot sunny day. And, like humans, small plants eat and drink less than adults (though I’m not sure my children knew this!). so small plants need less water.

As a rule of thumb, I always give each full-size plant, with 5-8 trusses of fruit, about half a gallon of water a day when it’s hot and sunny. But that is appropriately adjusted if the plant looks like it needs more or less. For example, if I go into a greenhouse in the early morning and the plants have water droplets on their leaf margins I know they were over watered the day before. And if they look like their leaves are hanging down a fraction I know they are underwatered  The most subtle signs tell an experienced grower a lot about how the plant is “feeling” Good growers think and emphasise like a tomato!

Pollination

Tomatoes are self-fertile. And in nature, they don’t need bees or other forms of pollination.  The slightest movement of the flower dislodged the pollen from the male parts of the flower and they fall by gravity onto the female parts. Job done.

But when we grow toms indoors there’s no movement due to wind or animals knocking the plant. So we may need to assist. Tomato growers specialising in very early crops apparently sometimes use bees. I don’t know any such growers myself and think it’s a waste of time as there are easier ways. For example, where the plants are suspended on strings suspended from wires all that is needed is to tap the wire at the end of each row and that is enough. If the row is very long then walk down each row and brush past the plants. That movement is enough.

In my own case, I found walking up and down each row once a day too long winded and I used a hose pipe.  A good jet of cold water directed at each plant is quick and easy to achieve and raises the humidity a bit. Tomatoes that are too dry don’t pollinate correctly.

This strategy will perhaps dislodge the “don’t get the leaves wet” myth. Plants have evolved to cope with rain so the notion is a little silly really. However, I tended to use the hose pipe in the mornings.  I used to do it around 10 am as the temperatures had risen and the plants would dry before nightfall. This meant fungal diseases weren’t an issue.

Sideshooting, Topping & “Pruning”  Tomatoes

Let me start this section by saying you should NEVER prune a tomato. To “prune” means to cut the plant in some way. Some plants tolerate pruning and even benefit from it, but not tomatoes.  If you prune a tomato you leave a wound where fungal diseases can enter and cause things such as botrytis.

However, that’s not to say you shouldn’t remove leaves or sideshoots at the right time. But you do it by snapping the shoots or leaves which allows them to snap across the natural abscission layer that plants have. For example, when trees shed leaves in autumn they do it across a natural abscission layer between the leaf stem and branch. Tomatoes have similar layers which help us when we want to remove the leaves or sideshoots.

How to Grow Tomatoes: Sideshooting

If we want to grow our indeterminate tomato as a cordon plant, up a string or cane, we need to remove the growth that would make it bushy.

Between the stem and the leaf is an area called the leaf axil, and it’s here that a sideshoot grows.  If we leave it we get a bush. So we need to remove it. And it must be cut out or it will encourage fungal diseases.

If you take the sideshoot between finger and thumb and bend it left and right you’ll find it snaps off quite cleanly. It’s that simple.

Do this on a weekly basis, train the remaining cordon growth around a string (or tie to a cane) and the plant will grow quite quickly.

De-leafing Tomatoes

Tomatoes can get very dense with quite luxuriant growth when grown well. It looks great until you have to find the tomatoes for picking. If you’ve had this problem you’ll know how they hide behind the leaves!

the answer is to remove all the leaves to picking height a week or so before the truss is ready for picking. This not only makes them easier to see and pick, it also improves airflow which decreases disease risk AND it speeds ripening as the warmth of the sun can reach the fruit.

Deleting is very easy and quick. It’s rather like sideshooting. But in this case, hold on to the leaf stem and bend it upwards and then downwards. This will snap the leaf off at the abscission layer and leave a “wound” that heals quickly and limits the disease risk.

When to Harvest Tomatoes

There’s no right or wrong time to harvest. It’s a personal preference.

Commercially we needed to pick them, grade them for size and quality, send them to market or supermarket and get them on the shelves on the day the consumer wants them. So we picked when they were green but showing a hint of orange. If they were only going to the corner shop and would be on sale the same day we would wait for them to be a nice orange all over.

At home, I pick them when a little redder. I want them firm but nicely coloured.  And I like to eat them when a nice rich red colour .. but before they go soft.

But of course not everyone wants red tomatoes.  Each year, in autumn I would pick a lot of very green tomatoes for my local Indian community. They wanted them for chutneys and pickles and looked forward to the ones that were the “right ” colour for making these delightful dishes.

So pick when you want to …   and not when some book tells you is best. You know best!

Tomato Diseases

Tomatoes are remarkably problem free with one or two notable exceptions.

Tomato Blight

In all my years as a professional tomato growers I never once saw or heard of blight in glasshouse or tunnel grown crops. But its a deadly disease of outdoor diseases and inevitably strikes after 2-3 days of the right mix of temperature and humidity (Hutton Days). Essentially this means a few warm, thundery days. And in late summer in the UK these are common. So blight is also common. Blight warnings are available online, just Google for them and sign up for emails.

However, warnings don’t do a lot of good as they don’t prevent blight. It is however possible to avoid blight to a limited degree. Blight resistant varieties are available, and putting the plants in the right part of the garden works to an extent. This year I put some plants outside.  One batch has blight and the other is totally clear. They are the same batch of seeds and sowing, so essentially the same plants. The difference is one is in an area where humidity doesn’t build up quite so much and one is in a hollow where humid air sits.

I see people recommending during affected plants and not composting them. This might help a bit, though I have some doubts, as the spores are airborne and spread vast distances on the wind. And you only need one spore to set up the problem.

Botrytis on Tomatoes

Botrytis, Botrytis cinerea, is welcome on grapes and is known as the “Noble Rot“. It’s used to “raisin” the crop and produce certain superior wines.

But on tomatoes it is known as grey mould and is destructive. Damaged leaves and stems are the most likely to succumb and the grey mould slowly spreads, killing leaves and stems. But it is relatively slow spreading compared with blight. If I see any at all I tend to trim the infection away and nine times out of ten that’s the end of it.

Ghost Spotting

Ghost spotting of tomatoes is where a botrytis spore has germinated on a fruit and then died. It leaves a little halo blemish but is quite safe to eat. Amateur growers tend to get a bit of it as its harder to control humidity in a small greenhouse.

Should I Buy Grafted Tomato Plants? Are They Worth The Money?

In brief. No!

I don’t believe they deliver good value for money except when grown by professionals in the most exacting conditions.  Save your money.

There are more details of why I don’t recommend grafted tomatoes in this link .

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