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Most tomatoes grown in a Greenhouse will be indeterminate, and require to have all side shoots pinched out, leaving the flower shoots of course! Pinch out the leading shoot when it reaches the roof of the greenhouse, or when some 6 flower trusses have formed. Train the leading shoot up a cane or a length of twine, attached to both the roof of the greenhouse and tied underneath the grow bag. As the tomato trusses swell, the total weight of tomatoes on the plant can become so large that the tomato main stem can buckle or break. To avoid this happening, tie additional twine round the top of the stem and support it from the greenhouse roof.
For growing tomatoes outside, I would choose quick maturing, bush types, to try and reduce the problem of blight, but do not transplant them outside until all danger of frost is over in your area, in June. Even then, continue to provide cloche protection in the North for the rest of the month.
Warning. On no account plant out these sub-tropical plants before the last expected date for frost in your area. This could be mid May for the mildest areas such as Southern coastal areas, and early June in the North of the UK. Even then, provide cloche or fleece protection for the first few weeks as cold nights and winds will cause plant damage. Gardeners are regularly caught out by late frosts occurring during the traditional cold period known as “The Ice Saints”, usually just before mid May. Remember, one night of a late frost will kill your sub-tropical plants!!
Tomatoes require a high potash fertilizer which is usually provided by a proprietary liquid preparation. Some gardeners make up their own organic concoctions, but the difficulty is knowing how much dilution of the liquid in water is required. It would be quite easy to burn the roots of the tomato plant if the concentration is too strong.
Pests and diseases.
The worst disease is blight, especially for outdoor tomatoes, where you are quite likely to suddenly loose all your plants if the conditions of temperature and humidity are suitable for Blight. If you see your potatoes being attacked by Blight, assume that any outdoor tomatoes will be affected as well.
The weather conditions that are likely to lead to an outbreak of Blight, are known as “Smith Days”. This is when there are two consecutive days where the minimum temperature is 10 C or above. In addition, for at least 11 hours each day the relative humidity is greater than 90%. In other words, two days of particularly hot and sweaty weather!
You may have no alternative but to spray against blight with a proprietary pruduct though I am not keen on its use. Some degree of control can be obtained by erecting a shelter above the tomato plants by using a polythene cover, which prevents Blight spore laden rain water from falling onto the tomatoes.
It can also affect indoor tomatoes if the humidity and the temperatures are too high, especially in the late Summer and Autumn. In the greenhouse, remove any affected leaves to try and limit its spread.
Mildew can be a problem in greenhouse culture. An increase in ventilation can help to control it, or spray with a fungicide. Also snap off any leaves that are affected to stop the spores spreading in the air currents.
Splitting of the fruits is usually caused by erratic watering. It is important to make sure that the compost is not allowed to dry out and then made very wet. As home gardeners are more likely to grow choice varieties of tomatoes with thinner skins, this can be a problem.
Blossom end rot, where the blossom end of the fruit starts to rot, has a similar cause. However, some varieties of Tomato seem to be particularly prone to this problem. For instance, the variety “Black Russian” is prone to Blossom end rot, while I have never seen it on “Sungold”.
Greenfly, red spider mite and whitefly are all serious pests on tomatoes, sucking the sap and spreading virus diseases. Pay particular attention when bringing young tomato plants into your greenhouse and make sure that they are not already infested with these pests. If you see any signs of infestation, spray the plants thoroughly with a suitable insecticide. See Greenhouse Pests for suitable treatments for the control of such pests.
Tomatoes are best used fresh, and should be picked when each fruit is ripe and just starting to soften. Depending on the variety, in addition there will usually be a colour change in the fruits. To minimise the danger of the fruit splitting, the individual tomatoes should be gently snapped off their stem at the first knuckle joint above the fruit, leaving the green calyx and about a cm of stalk attached to the tomato. This works well for cherry tomatoes, but you may well have to cut off bigger tomatoes, to minimise splitting.
You may be surprised to learn that a bunch of Tomatoes does not naturally ripen all at once, as sold in shops as “vine tomatoes”. They achieve this affect by using a variety that has tough skin, and has an ability to prevent the ripe tomatoes from going soft. Even so, they usually have to cut off and waste the green end tomatoes. Naturally, tomatoes ripen in sequence from the main stem to the end of the bunch, and need to be picked in sequence, as and when they are ready.
In times of a glut in the Autumn, consider bottling or freezing them as a puree, using them for soup or making a tomato pickle or chutney.
At the end of the growing season, say November in the cold greenhouse, you are quite likely to have quantities of green or semi-ripe tomatoes still on tomato plants, that are never going to ripen in those conditions. However, if they are carefully picked and placed on shallow trays in a sunny windowsill in your house, most will eventually ripen, even if it takes till January. Nothing like your own tomatoes in the middle of Winter! You can use the same trick to try and improve those ghastly, insipid, shop-bought tomatoes available in the Winter.
Go to Tomato Varieties.