"Steve Upton" wrote
I have been growing some tomato plants in grow bags outside, 3 Alicante
and 3 Sweet Millions. They are good strong plants with lots of blooms
and nice thick stems. Each plant is about 4.5-5 feet tall.

I have created a water mechanism that consists of 2 x 2ltr drink
bottles with the bottoms cut off and a tube stuck into the top of the
bottle. I have put the tubes down into the grow bags so this will water
the tomato plants directly to the roots. I just fill up the bottles each
night and I know I have given the grow bags 4 ltrs of water each night.



Everything looked great up until a few nights ago, I noticed that some
of the Alicante newly formed tomatoes have started to produce black
bottoms where the bloom was. I am assuming this is Blossom End Rot. The
other Alicante plants in the same grow bag looks unaffected and the 3
sweet millions in the other grow back look very healthy.
The questions a

I am over watering the tomato plants? I was under the impression that
tomatoes love water when producing fruit.

The soil is certainly moist all the time, as the weather has not been
very hot recently. But I have put holes in the bottom of the bags for
drainage. I am not getting a huge amount of water loss from the bag
when watering.

I also understand that Blossom End Rot is a cause of calcium
deficiency. Can I add calcium to the grow bags to prevent the other
tomatoes suffering this problem? If so how?


Causes of Blossom End Rot are dry roots and/or acidic soil.

If your growbags are always moist then it must be the pH, worth checking.
If it is the pH then they were not good quality growbags and I would suggest
you don't use the same manufacturers again (and let us all know the
culprit).
The small fruiting varieties of Tom do not seem to suffer this problem.
If you use rainwater to water try using tap water provided it's hard water.

--
Regards
Bob Hobden