Thanks to John Harrison of Allotment & Gardens
Unfortunately, tomatoes are not the easiest crop and are often misunderstood but tomatoes are well worth growing in the UK – even with our cool climate and uncertain weather.
Now the tomato is originally a South American plant (it’s true!) that requires better weather than we can usually offer. If you can provide shelter, such as a greenhouse, polytunnel or grow house you will get the benefit of a longer season, some pest and disease protection and a better ripened crop.
You can successfully grow tomatoes outdoors in the British climate but it is less certain. Tomatoes require a minimum temperature of 10deg C and high light intensity to grow. They are not hardy at all and even a light frost will both kill the plant and ruin the fruit.
Tomato Types and Varieties
The first thing to decide is what varieties you wish to grow. The tomatoes you buy from the supermarket are chosen for their travelling and keeping qualities, probably grown abroad and fed with inorganic chemicals. Taste may be factored in some way down the list of their choice.
As you will only be transporting a few yards and keeping for a day or two you can ignore those factors and concentrate on the taste and ease of growing. Some tomato varieties are better suited to a greenhouse environment and others more able to grow outdoors in our climate.
There are a huge number of tomato varieties and types of tomatoes to choose from. Some are tried and true standards that produce consistent fruit similar to those you find in the shop and others a little different. I have yet to see Sungold in a shop to buy but it is one of the most flavourful sweet small salad tomatoes you will taste.
Heirloom Tomatoes (Heritage Tomatoes)
These are older and often rare varieites prized for their flavour. More information on Growing Heirloom Tomatoes
Types of Tomatoes
Cordon or Indeterminate Tomato Varieties
These tend to be the most grown types, usually tied to a cane or string and the side shoots are removed to ensure the plants energy goes into the fruit rather than foliage. When a number of trusses (The plant stalk that bears the flowers and fruit) are set, the plant is stopped to allow the fruit a chance to ripen before the end of the season.
Bush or Determinate Tomato Varieties
Bush tomatoes differ in that they do not need side shoots removing and are effectively self stopping. The drawback of this is that they take up more room and are not so suitable for growing in pots. They do not generally require much or any support but the fruits are often in contact with the ground, which means more vulnerable to slugs and other pests. They can, in poor years, leave you with more green and under-developed fruits but you can compensate for this if you can get them off to an early start.
Dwarf Bush or ‘Hanging Basket’ Tomatoes
Unlike the standard determinate varieties of tomato, these are smaller plants usually giving cherry tomatoes and are bred to grow in containers such as hanging baskets. My experience is that they can be very successful.
Tomato Fruit Types
As well as plant types there are quite a number of different tomato fruit types. As a home grower, you can find many different – some weird and wonderful – varieties but the main types of fruit are listed below:
- Standard – the ‘normal’ tomato, spherical in shape and around an inch to an inch and a half in diameter.
- Cherry – just a small version of the normal tomato, often marble sized. Often from dwarf bush types.
- Beefsteak – a large version of the normal tomato. Because of their large size, these tomato varieties take longer to mature and ripen so really do not do well except in a greenhouse.
- Plum – the firm fleshed oval shaped fruit you find in Italian canned tomatoes. Tend to have been bred to store well as bottled (or canned) and they freeze well. (See Storing the Surplus)
- Marmande – large irregular shaped tomatoes. Often very tasty.
- Oxheart – cone shaped fruits, usually firm fleshed and good flavour.
Tomato Colours
Tomatoes come in a range of colours from deep reds through orange (often described as yellow) to bright yellow with some rarer varieties being striped, green when ripe and very dark purple to black.
Colour has little to do with flavour – my favourite tomato, Sungold, is orange but other yellow tomatoes I have tasted are not very nice which may or may not be related to the colour.
Sowing the seed
I start off all my tomatoes in the same way between late February and early March by sowing thinly into a standard multi-purpose potting compost in small 2½” pots, lightly covered with compost or vermiculite and placed in a heated propagator at 20ºC. A warm windowsill will also suffice.
My experience has been that starting tomatoes off too early is counter-productive. The day length is too short and the light intensity too low to get strong seedlings. Consequently the seedlings become ‘drawn’ – long, thin spindly shoots trying to get out of the shade into the sunlight, which is just not there. Although you can rescue these by planting deeply, later sown seeds seem to catch up and even overtake the earlier.
Also, when moved into the greenhouse, it is harder to maintain a reasonable temperature – unless you can afford a heated greenhouse. Even in mid-March you need to watch out for really cold nights. In Britain we hardly have climate but we do have weather!
To defend against cold nights I place horticultural fleece over the seedlings, using some short sticks to keep the fleece from pressing down on the seedlings.
Potting On the Tomato Seedlings
When these have germinated and are about an inch high, I move them into individual modules in a seed tray, which are grown on in the greenhouse. Research has shown that they do best if transplanted within 6 days of germination. Pots indoors will do if you do not have a greenhouse.
When they outgrow the modules, I select the best and move them on to 3″ pots. I always ‘plant deep’, about half way up the stem at each stage. This encourages root formation, which the plant will need to supply the demands I am going to make upon it.
You could probably cut out the module stage – but I always expect to lose a few seedlings on transplanting so this gives me ‘spares’. Moving from modules to pots does not place any strain on the plant so I do not plan on losses at this stage.
Some particularly vigorous varieties may need to move to an even larger pot before they reach their final position.
You can, of course, buy tomato plants from nurseries but generally I prefer to grow my own from seed as you the range of varieties to buy as plants may be limited.
Moving the tomato seedlings on – how to pot on tomatoes
The module insert is filled with an ordinary multi-purpose compost.
By planting deep the plant is encouraged to form more roots from above the old root line.
Usually these would go out into the deep propagator in the greenhouse.
In very cold weather or lack of warm green house, the modules with the tomato seedlings are brought on in the window sill.
Unfortunately they do get drawn by the lower light level. Fixing some kitchen foil to cardboard and standing this behind the modules will help by reflecting more of the light on to them
This is the point where my treatment of the tomato seedlings changes according to whether I am intending to grow them as outdoor tomatoes or under glass.
Growing Tomatoes in a Greenhouse
Growing tomatoes in a greenhouse is far more certain to produce a good crop than outdoors as you control the climate. In fact, I would not even try to grow outdoors in the ground north of the Midlands in the UK without some extra shelter.
The problems that beset tomatoes due to irregular watering like split skins and blossom end rot are rare in border grown plants as are problems like magnesium deficiency as the larger volume of soil in a border is more forgiving of our mistakes – diluting fertiliser overdoses.
The disadvantages of growing in the border soil are these:
- Properly preparing the border soil can be quite a lot of work.
- The soil in the border will require changing to avoid a build up of diseases
- Pests like slugs can be lurking in the soil
- Weeds growing in the soil
- Evaporation from the border soil increasing humidity beyond what you want
Luckily the last three points can be overcome quite easily but preparing and changing the soil is still a task to consider.
Preparing the Greenhouse Border Soil
The ideal tomato border will provide nutrients for the plants and retain water without becoming waterlogged.
In winter or very early spring, dig out the existing soil, at least a spade depth or more if you can. Break up the sub-soil at the bottom with a fork.
Next add a thick layer of home made compost – at least 6” deep but more is better if you can. If you have wood ashes available, add an ounce per square foot or a tenth of that amount of sulphate of potash.
An ounce of calcified seaweed per square foot will assist microbial action in the soil.
Top off with a layer of sieved garden soil mixed with commercial multi-purpose compost or leafmould. The bed should be mounded and high at this stage. Over the next months the bed should sink. If it is low at planting time, add some more soil / compost mix.
One serious tomato grower reckons his success is due in part to putting a layer of sheep manure in at the base of the greenhouse border with the compost. Sheep manure is high in potash compared with other animal manures.
Ideally you should repeat this process every year, digging out the old soil for use in the garden. In practice you can get away with every other year so long as you use more liquid feed such as comfrey liquid or commercial tomato feed to compensate for the nutrients having been used.
Do not use the soil removed from the greenhouse border on a potato bed – these are the same family as tomatoes and use similar nutrient ratios.
Pest and Disease Problems in Greenhouse Borders
The biggest pest problem has to be slugs and snails. These are easily dealt with by using beer traps or safe slug pellets. Personally I prefer the pellets but just use whatever method you prefer.
If the soil hasn’t been changed as described above for a few years you will get problems of diseases building up and nutrient deficiencies developing.
Some growers swear by sterilising the soil in the greenhouse border by drenching with dilute Jeyes Fluid or the like. This will kill any latent disease but at the cost of killing all the microbes and worms. Friend and foe alike will be killed.
The complex natural system which helps plants absorb nutrients is wiped out. I have seen no trials or studies but I strongly suspect the vitamin content of the fruits will be lower and flavour inferior.
Weeds & Evaporation Causing too much Humidity
Just as on the plot, weeds are easily handled when small. Once they grow pulling them can damage the roots of your tomatoes.
If, instead of just watering the surface you insert half bottles into the soil and water into those, the surface will remain dry but the tomatoes will have water. The dry surface will stop any weed seeds germinating and prevent evaporation increasing humidity.
Another method is to lay a covering of white plastic over the greenhouse border. You can either buy the plastic or cut things like fertiliser bags to form sheets. The white colour has the benefit of reflecting light up onto the plants, helping fruits to ripen.
Do not use black or clear plastic as this can over-heat and cook the plant roots, killing your crop.
You can water through bottles as mentioned above or use a drip hose under the plastic to water.
Supporting Cordon Tomatoes in the Greenhouse
As your tomatoes grow, they’ll require supporting. There are two main methods – string supports or canes.
Stringing Tomatoes – How to String Support Tomatoes
Commercially and traditionally cordon tomatoes have been supported on string. This is anchored at the base of the plant and taken to a point usually on the greenhouse roof.
Once the plant has reach about 18” (45cm) high it is likely to flop over and it is time to string it.
The string is tied to a convenient cross-bar or point on the frame above the plant. It is taken down to the plant and tied to the plant by creating a loose noose at the base. Then it is wrapped around the plant a couple of times
As the plant grows the twine is twisted around the plant supporting it. It is very easy to do and quick to continue as the plant grows. Initially do not put too much strain on the plant or you can pull it out of the pot or border.
Pole or Cane Supporting Tomatoes
The other method for supporting cordon tomatoes is to insert a bamboo cane by the plant and tie the stem to the cane as it grows. I use a figure of eight with the string so the plant stem has room to expand as it grows.
Commercial growers grow cordons at an angle rather than vertical. Those guys know what they’re doing and if you have the room it may increase yield – although home growers are looking at just 5 to 7 trusses not the 25 + trusses of the commercial grower’s tomato plants.
Ideal Temperature for Growing Greenhouse Tomatoes
The ideal temperature would be between 20ºC and 24ºC in the day, allowing it to drop to no lower than 18ºC at night. You can get away with lower temperatures but most harm is done by home growers allowing their greenhouse to overheat in the summer.
Feeding Greenhouse Tomatoes
The feeding regime for tomatoes is quite straightforward. When the first truss has set, which means the flowers have gone and you can see tomatoes beginning to form, it’s time to start feeding. Begin feeding either with a commercial feed as per the instructions or home-made feed such as comfrey liquid on a weekly basis.
I would always use a good quality commercial feed with trace elements to prevent magnesium deficiency rather than cheap commercial feeds. Towards the end of the season, I replace one feed in three with a high-nitrogen general feed such as Miracle Gro. It seems to help the plant maintain its general health and extend productivity.
Side-shoot (Sucker) Removal from Cordon Tomatoes
Apart from feeding and watering, with cordon tomatoes in the greenhouse you will need to remove side-shoots to encourage fruit production and stop the growth towards the end of the season.
End of Season
As the season draws to a close, it becomes a race to ripen the crop prior to the frosts. To help this along, remove the lower leaves and expose the fruits to the sun. By this stage the plant does not need as much energy so the leaf removal will not affect it.
At the end of the season before the first frost, harvest all the green tomatoes of reasonable size and these can either be ripened or used in chutney etc.
You can also hang up the vines with fruit on in a frost-free, cool dark place and they will slowly ripen. If kept in a bowl with a ripe banana they will ripen quickly due to the gas given off by the banana
