It can be so hard to keep plants from stress as most of it is weather related.  I don't know of any home made fix for this problem,  but there is a product called  Bonide Rot-Stop, round here you can buy a pint of concentrate for about $8.(That amount does us a couple of years or more).   After you mix it up you spray it directly on the plant leaves either early in the morning or evening, but only under stress conditions. It contains 9.2%  calcium from calcium chloride.   It works for us, we were almost flooded out twice in two weeks then it turned off hot and dry I noticed the rot starting and sprayed and we seem to be doing O.K. now.  Like always you have to read the label carefully it is not for regular use,  to do so may cause leaf burn.   Hope you find a solution as it is heart breaking to lose your tomatoes.  

I know several people who recommend dissolving epsom salts in your watering water on a fairly regular (every other watering, or monthly) basis (though this advice comes from those who garden in containers, so in-ground gardeners, YMMV).

Thank you for all the input! … if I'd had any idea that BER was this typical, particularly with our CA valley heat, I wouldn't likely have become so frazzled over the years with the larger, heavier tomatoes.   Veggie gardeners close to me are basically fumbling along with about as much adeptness as I!   It'll now simply become SOP each year to make sure all the tomatoes and peppers have their roots happy with ample nutritive prevention … and then be ready to lose a few early fruits with the first heat wave!

With the latest high heat …. another 103 predicted for today, hoping the surprise breeze will mitigate that … I'm now covering the tomatoes and peppers with sheets during the afternoon to help ease sunburn.  My peppers ain't so happy now as they're lookin' a tetch crisped!    

Now if I could just convince the   dog from filching the ripe tomatoes from the vine I think I'd finally be gaining a grip on the full range of pests!

It is tomato time, again and time for all the problems that entails. My first little green tomatoes have appeared in my global buckets and I am looking to keep blossom end rot away. We have had a particularly wet spring and I imagine all nutrients have been leached out of my planting soil. I see people have recommended Epsom salts, but I'd have no idea of how much to use. How much to a gallon of water would you suggest?  Dumping a gallon of water down the tube seems to work much easier for me that hauling out the hose.

I also remember my mom soaking eggshells in water to water her house plants. The water was supposed to leach the nutrients out of the shells. My dad hated it 'cause the whole house smelled of sulfur when those shells had sat a couple of days, but Mom always had beautiful house plants. Since the problem with BER is lacking calcium, would eggshell water work instead of Epsom salts or wouldn't it be strong enough? Does anyone have any experience with this? If you are worried about DH being stinky-d out of the house, like Dad was, I promise I'll keep them on the back porch. LOL

This advice isn't for this year, but if you're having persistent problems with BER, get a soil test done, and specifically sample your tomato growing area, or in fall (which is best), take your soil samples from the area where your tomatoes will be grown next year.  Sometimes it's not so much the lack of calcium, as a low ratio of calcium to other nutrients such as nitrogen or potassium.  We grow 400-600 tomato plants a year to sell at the farmer's market, and the balance in nutrients is much more important than just calcium.  We also use epsom salts to mitigate BER, but make sure our nitrogen and potassium are adequate also.