Blossom-end rot (BER) is due to a lack of calcium in the distal end of the fruit (the end where the flower dropped off) opposite the calyx (where it is joined to the plant). Sometimes there is an internal black rot with little or no external signs. It is seldom due to an actual deficiency of calcium in the growing medium or soil. Calcium is taken up passively and carried in the 'transpiration stream'. It can only be absorbed by actively growing root tips.
All this means that there can be several underlying causes:
Take off all the affected fruit (it tastes bitter). Try to maintain an even amount of moisture in the soil or growing medium. Feed with a high potash feed once the fruit start to swell, according to the instructions on the packet. If the plants are growing in a greenhouse, don't keep the vents closed during humid weather, leave slightly open. Plum and beefsteak tomatoes are much more prone to this disorder than cherry varieties.
Uneven ripening and fruit that tastes ‘flabby’ (low acidity) is usually due insufficient potassium. Feed every watering with a high potash tomato feed. Have your soil analysed and apply potassium fertilizer before the next crop (if required).
Symptoms are yellowing of the older leaves with the main veins staying green.
This can be due to a number of causes:
Removing the underlying cause should alleviate symptoms. Use a liquid feed which contains magnesium as well as potassium. Have your soil analysed and apply magnesium fertilizer before the next crop (if required). If it’s really bad you can spray with 1 litre per 10 sq m of a 2% solution of Epsom’s salts, with a little washing-up liquid as a wetter. Be careful, as this can scorch the leaves if done in sunny conditions.
Symptoms are yellowing of the very youngest leaves at the top of the plant, with even the smallest veins remaining green; usually caused by over-watering and/or poor soil aeration.
It can be treated by spraying with a proprietary iron foliar feed, but you also need to fix the underlying cause.
‘In early summer, the nights can be cold and the days very warm. This fluctuation of temperatures is the main cause of what can sometimes be a very alarming degree of leaf curling. The plant is unable to cope with the accumulation of carbohydrates that occurs if nights are too cold for plant physiological functions to occur normally. Fortunately this does not seem to be a serious cause of loss of crop and usually disappears of its own accord as the nights begin to get warmer in late summer.’
Information taken from RHS website Tomatoes: leaf problems
Did You Know?
British Tomato growers use an army of over 40 million beneficial predatory bugs called Macrolophus in summer to keep pests out of their crops, reducing the need for chemicals.