could be lack of minerals. but blossom end rot isnt lack of water but erractic watering. so wet enough most days followed by a very hot day so the plant loses a lot of water would cause it. try a decent tomato feed such as tomorite.

</p><p> thank you seaburngirl

Some varieties seem more prone to it too I think, the last few seasons have not been good for growing tomatoes even in the greenhouse

</p><p> thanks pamg