27 June, 2017

July 2012

GREENHOUSE TOMATO PROBLEMS.

I’m sure that holidays are far more in your mind than gardening at this time of year. However, it’s the season when events are most likely to overtake you; particularly if you disappear to the Med. for a couple of weeks or so.

As you might imagine, the greenhouse is where things can go wrong soon and quickly. It only needs a couple of greenfly to get together when you’re away for there to be a nasty shock waiting for you when you get back. Much the same can be said for fungus diseases.

 On the physiological side (problems caused by neither pests nor diseases), it’s odd but tomatoes, in spite of being such a popular crop, seem to attract a disproportionately large number of horrors.

They’re also more susceptible than most other things.

One of the most confusing is their apparent inability, on occasions, to set fruit properly.

The cause can usually be boiled down to too dry an atmosphere but it can also be a failure of the anthers to release the pollen to fertilise the flowers. No fertilisation, no fruit.

Fortunately, there is one remedy to cure both problems; spraying overhead with water. I know it’s sopping wet outside but it can still be bone dry in the greenhouse.

This should be carried out two or three times a day when it is hot and sunny so that it will not only help to set the fruit but also keep the plants cool and the atmosphere moist. If this doesn’t do the trick, I’d take up stamp collecting instead.

Incidentally, the moist atmosphere greatly reduces red spider mite as well.

Disorders

When tomatoes are nearly ready for picking, a number of these physiological disorders can occur. They are problems caused by the conditions under which the plants are growing; not, as I have said, by pests or diseases.

 

One thing that has plagued gardeners since tomatoes became a cultivated crop is a disorder called ‘greenback’. Here, the stalk end of the tomato fails to ripen and stays green and hard.

The generally accepted cause is exposure to too much strong light. The most successful answer is to grow a modern and resistant variety. Moneymaker, Alicante and Shirely are three such varieties but the seed catalogues are full of others and they always tell us what individual varieties get and don’t get. Alternatively, make sure that the greenhouse is shaded properly.

‘Greenback’ is a problem that is often brought on by de-leafing the plants too much so that there is inadequate shading for the ripening fruits.

De-leafing improves the air circulation amongst the plants so that fungus diseases are greatly reduced. However, the removal of too many leaves exposes the fruit to more sunlight than is good for them so, if greenback appears, don’t take off so many leaves.

‘Blossom end rot’ is as spectacular as it sounds. A small black area appears where the flower used to be and slowly enlarges until it can be as much as an inch across.

Although, technically, it is a symptom of calcium defiency, in practical terms it almost always happens because of uneven watering.

Fruits of any age can display the symptom but it is often not until they are ripe and picked that the problem is noticed. The black end is usually facing the ground until then.

The best remedy is to pay more attention to the watering so that the compost does not go from extreme dryness to extreme wetness and then back again.

A good way of achieving this is to rig up a semi-automatic watering system using strips of, say, capillary matting.

These should be led from a bucket or bowl of water into the containers in which the tomatoes are growing.

Those plants growing in the greenhouse border or planted outdoors seldom suffer from ‘blossom end rot’ as the large bulk of soil available to the roots is much less likely to dry out.

Various other appropriately named horrors, such as ‘blotchy ripening and ‘bronzing’, may turn up from time to time but most are attributable to the growing conditions and can quite easily be avoided by paying more attention to ventilating, shading and watering.

Above all, enjoy the sun when it comes!

 Peter Blackburne-Maze

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