Have you ever had that sinking feeling when, after months of careful nurturing, just as your tomatoes are ripening there on the base of the fruit is a disk of hard black tissues – Blossom End Rot (BER).
The first question is ‘How has his happened’ swiftly followed by ‘What shall I do?’ BER occurs when the calcium levels in the fruit falls below 0.5%. Calcium, as calcium pectate, is the glue which sticks the walls of the cells together. With insufficient calcium, when the cells are under stress they implode and BER occurs.
This may happen as early as 3 weeks after fertilisation when the rapidly expanding fruit needs more calcium than is being transported up the plant. Water is the key. Calcium is transported up the plant on the water stream. The answer is to keep the beds, containers, and particularly growbags, consistently and uniformly moist.
This assumes that there is sufficient calcium in the soil or compost to be transported to the plant. Before planting, a simple soil test with an inexpensive pH soil test kit will confirm this, if it shows a reading of between 6.25- 6.75 this is fine. Should the level need adjusting, of the liming materials available, dolomite limestone with its 50-60% calcium carbonate and 30-40% magnesium carbonate is the tomato growers favourite as it adds magnesium to the soil. Magnesium being the central atom of chlorophyll, and needed by the plant to help ward off magnesium deficiency.
So keep the plant moist, if on doubt put your hand down 4-6” / 10- 15cm and feel the moisture, your hand may get dirty but it wards off the sinking feeling that BER brings.