hi Pattie,

I'm sorry to hear about your tomatoes!   From what I can see, that is indeed blossom-end rot.  Though it is caused by a local (at the level of individual cells) calcium deficiency, adding calcium to the soil is not the solution.  Rather, making sure the tomatoes are evenly watered should allow new fruits to develop normally.  Water deficiency makes it impossible for the plant to move calcium to the rapidly expanding fruits, resulting in the brown spots.  Tomatoes growing in containers are especially vulnerable.  Make sure they are getting thoroughly watered at least once a day--in extreme heat, it might need to be more often.  You could also consider a light shade cloth to help them stay a bit cooler.

I hope this helps!

Cordially,

John

You could consider it in a couple of ways.  In (likely) order of ease of implementing:

  The first is yes, "too much sun"--shading or moving the plants could help.  The second is "too small container"--potting the plant up into something larger could help.  The third is "not enough water"--you could add a saucer to the bottom to provide water for longer through the day to the growing medium, or water twice a day.  

I hope this helps!

John

Don't give up yet!  You still have plenty of growing season to get some nice tomatoes, and even those affected by blossom end rot are edible and tasty.  Just remove the brown portion and proceed as normal.  I use them in sauce!

Good luck!

John