blossom end rot ripe.JPG

Blossom end rot unripe (2).JPG

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.

Blotchy ripening

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).

Magnesium deficiency

Symptoms are yellowing of the older leaves with the main veins staying green.

This can be due to a number of causes:

  • Low soil magnesium levels (especially if potassium level is high)
  • Root problems caused by waterlogging, disease, over-application of soluble fertilizers
  • Stress due to heavy fruit load

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.

Iron deficiency

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.

Leaf curling

‘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

plant made a full recovery after repotting in fresh compost plus liquid feeding.jpg This tomato plant looks starved.jpg The compost looks very wet and the roots aren't healthy.jpg

Fact 08

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