I've had blossom end rot (BER) on virtually every San Marzano (Roma style) tomato in both my community garden and my home garden. The scourge has not struck any of the other tomato varieties. Apparently paste tomatoes are more prone. I wondered at first if it was my seed, but two other urban gardeners to whom I gifted some of my seedlings, have not encountered such problems. I realized it must be the soil and a lack of calcium.
As a quickie measure I crushed up some of my calcium vitamins and sprinkled them over the soil around the San Marzanos a week ago. The results have been remarkable. Take a look at the these four tomatoes. You can almost see the tomatoes in four stages of healing themselves. The first on the left is full blown BER. The next has survived a little further. The third bulged out a new section of growth from where it had begun to rot and the forth has survived.
It's been a drag losing so many paste tomatoes to BER. I've been cutting the end rot away and making sauce, adding in some yellow tomatoes to fill out the pan.
I have plenty of yellow tomatoes to spare.
With the addition of the calcium I have hope to harvest more paste tomato sauce for my winter storage.