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.