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 high potash fertilizer before the next crop (if required).
Early in the season, there can be large differences in temperature between the warm, sunny days and cold nights. These wide diurnal fluctuations can cause the leaves to roll up or curl. This is due to large amounts of carbohydrates accumulating in the leaves because the nights are too cold for the plants to assimilate them. It is usually a temporary problem that cures itself as the nights get warmer.
Disorders usually indicate that something is wrong the growing environment, watering or nutrition of the crop.
Disorders of tomatoes – page discussing disorders – Blossom-end rot
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:
- erratic watering, especially in peat bags
- sudden transition to low humidity after a period of dull weather
- root damage
- surge in vegetative growth due to high Nitrogen liquid feed or fertilizer, particularly if there is a high proportion of ammonium rather than nitrate-N
- excessive fertilizer or feeding
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.