We are often asked the question “Nearly every year the first tomatoes produced in my greenhouse develop hard, dark areas on the base of the fruits. I have tried different varieties, changing the make of the growing bag, different fertilisers, etc., but the trouble always occurs. As the season progresses, the problem goes away.”
The problem described is known as blossom end rot, and is caused by a lack of calcium in the developing fruits. This may be due to low calcium in the compost, or the lack of uptake caused to too little or irregular watering.
Blossom end rot can be largely prevented by using a tomato fertiliser specially formulated to include adequate calcium. Tomorite and Doff Tomato Feed are two good products to opt for. As well as calcium, they both contain a wide range of trace elements so would be a suitable choice to use this season.