If you grow paste tomatoes, they are more prone to BER than other varieties. Cherries and heart varieties are pretty much immune, but any non-paste variety would be a safe bet.

Linda

Yeah is is called BER (Blossom end rot) and probably the most frequently discussed topic on this forum for decades. There is even a FAQ here about it in addition to the hundreds of discussions about it the search will pull up.

But to determine which of the contributing factors are causing it for you we'd need much more detailed info from you on your growing methods. These are all contributing factors:

your location, climate, weather

your planting date

varieties grown

container or in ground

if container what size and what mix used

water and feeding regimen

Dave

Blossom End Rot FAQ

BER discvussions

How many tomatoes are you losing to BER? Just a few early on, or loss of many fruit all season?

BER is actually caused by inadequate calcium uptake into the plant. It may or may not be due to inadequate amounts of calcium in the soil. It you have large quantities of soluble salts in the soil (ammonium, potassium, magnesium, or sodium), calcium uptake by the plant will be interfered with. I'd get a soil test and see what's going on. Not sure where you are, but if your soil substrate is limestone, you sure won't want to be adding any calcium. By the same token, too much calcium can lock out other micronutrients. So be sure you're pointing your chemical shotgun in the right direction.

What kind of watering schedule do you have? Uneven watering can be a big cause of BER, and some varieties are more susceptible.

It's NOT lack of calcium. Recent research showed that the calcium in the fruit was normal until AFTER the damage ...

Anything that causes erratic moisture supply: poor watering practices, hot spells, dry spells, etc. can provoke it. It usually affects the early fruits, less so the later ones when the roots are larger and plant more mature. Seldom affects all of a season's production.

Some varieties are more prone to it than others - my "Roma" style had it, others didn't. Large varieties are more prone than small.

To minimize it, keep the soil consistently moist (check with a moisture meter), use mulch and plant small to medium sized varieties. Afternoon shade in hot dry climates might help.

lazy_gardens: Recent research showed that the calcium in the fruit was normal until AFTER the damage

Links or citations? I would love to read about this.

We are simply rehashing all that has been discussed umpteen times before without more info from the OP.

The links to the research showing adequate calcium in the fruit after harvest but which was mal-distributed, poorly distributed, throughout the fruit in its early stages of development have been posted umpteen times here. Carolyn posted them repeatedly several years back and they are have come up many times since then. So I'm sure the search will pull them up and are available on the web via a Google scientific search.

But it is beating a dead horse. So many insist on holding onto the "lack of calcium" claim because (1) the fertilizer industry encourages it, and (2) it sounds like it should be easy to fix and we all love quick fixes. We all want a guaranteed cure for it and the simple truth is no actual cure exists. There is only a list of things to help prevent it as much as possible and a list of things to AVOID doing. BER in tomatoes is a fact of life.

For starters but hardly all:

https://www.google.com/search?q=maldistribution+of+calcium+in+tomato+fruit+BER&rlz=1C1CHBF_enUS749US749&oq=maldistribution+of+calcium+in+tomato+fruit+BER&aqs=chrome..69i57.17825j0j7&sourceid=chrome&ie=UTF-8

https://www.google.com/search?rlz=1C1CHBF_enUS749US749&q=scientific+articles+on+maldistribution+of+calcium+in+tomato+fruit+BER&oq=scientific+articles+on+maldistribution+of+calcium+in+tomato+fruit+BER&gs_l=psy-ab.3...2847.8261.0.10588.13.13.0.0.0.0.137.1316.9j4.13.0....0...1.1.64.psy-ab..0.1.112...35i39k1.OfQq7GH6A-o

Dave

Thanks to you (Dave) and Carolyn and others, my understanding for a while has been that it's not about lack of calcium (except in certain situations such as incorrectly managed hydroponic or container growing) but problems in the plant getting calcium to crucial fruit tissues when they are in a key phase of formation. I have also explained it this way to many beginner growers on this forum and elsewhere.

But lazy_gardens was a bit ambiguous and seemed to be saying that it's not about calcium at all. It was unclear whether or not s/he was trying to say that the BER affected portions of the tissue in the fruit had normal calcium or whether the fruit as a whole had sufficient calcium but the affected tissues did not.

This is why I was interested in seeing any links to the mentioned research so that I could read it for myself.