Blossom End Rot in Tomatoes

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Blossom End Rot in Tomatoes by Richard Bailey, Wellington, Surrey

Most of us have had tomatoes suffering from blossom end rot at some time - the base of the fruit flattens, eventually becoming concave, and goes brown, remaining hard, despite the name "rot".

What is Blossom End Rot?

The condition is a physiological disorder, caused by an imbalance of potash and calcium in the compost, which most often develops if the compost is allowed to dry out while the fruits are swelling. It is more common, therefore, with container grown plants than with plants growing in the open garden or greenhouse borders. It is most common of all, however, when plants are grown in grow bags, where they have a small, shallow root run that dries out easily.

Prevention of Blossom End Rot

Once a fruit is affected there is no cure but further occurrence is most easily prevented by ensuring that the compost never dries out. Often difficult to do if you are out at work and cannot water the plants three times a day. Alternatively, a foliar feed with calcium nitrate will help to restore the proper balance of nutrients which is so often upset by overuse of high potash fertilisers.

The problem with grow bags can be alleviated, however, by placing an 8 inch (17 1/? cm) deep, 8 inch diameter, ring full of compost over each of the three holes made in the growbag and setting your tomatoes out in these rings. This gives each plant extra compost and a larger root run which will not dry out so quickly.

Varieties of Tomato Susceptible to Blossom End Rot

Finally, two simple observations - first, this year I had grow bags along a south facing wall, where they received no rain. Each one contained three plants of one of the following cultivars 'Ailsa Craig', 'Alicante', 'Britain's Breakfast', 'Golden Sunrise', 'Moneymaker', 'Super Sweet 100', 'Sweet 100', Tom Thumb' and 'Yellow Perfection'. All were treated identically and quite deliberately in a way that encouraged blossom end rot. 'Alicante' was seriously affected (about 35% of the fruits), 'Moneymaker' and 'Ailsa Craig' each had about 25% of the fruits affected while on plants of 'Yellow Perfection' and 'Golden Sunrise' less than 10% of fruits were affected. Once my curiosity had been satisfied, and regular watering recommenced, no further blossom end rot occurred.

Second - I have never known a small fruited tomato suffer from blossom end rot and at one time or another I have grown 'Gardeners Delight', 'Minibel', 'Mirabelle', 'Red Alert', 'Red Currant', 'Sub Arctic Cherry', Tumbler' and 'Yellow Currant' as well as those listed above. Nor have I known a plum shaped cultivar affected, and I have grown 'Britain's Breakfast', 'Roma' and 'Yellow Plum'.

Other Crops that suffer Blossom End Rot

Sweet and chilli peppers also suffer from blossom end rot, so can aubergines. Neither, however, are as susceptible as tomatoes.

This article originally appeared in the Members Bulletin, the journal of the National Vegetable Society, which is sent quarterly to members. You can Join the National Vegetable Society here

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