Obvious cause: erratic water supply. Very common in pot-grown tomatoes.

See Tomato FAQ at http://faq.gardenweb.com/faq/tomato/

Here is a link that might be useful: Tomato FAQ

Another obvious cause: Blossom End Rot.
Common in container grown plants.
Caused by insufficient calcium.
I have had really good luck with a spray
I got from a nursery.
I don't remember the name,
But I'm sure if you ask at your local nursey
They will recommend something for you.

And good luck! ! !
It is really discouragng
to have the fruits go bad
before you ever have chance to eat any!

Rusty

Our favorite tomato expert Carolyn137 wrote an excellent response to a question about Blossom End Rot (BER) and I am quoting it here:

With BER there is NO problem with absorption of Ca++ though the roots. The problem is maldistribution within the plant that can be induced by a number of stresses which include uneven delivery of water, too much N, growing in too rich soil, too hot, too cold, too wet, too dry you name it.

As the plants mature they can better handle the streses that can induce BER so usually it goes away.

The two exceptions are first, if the soil has NO Ca++ as confirmed with a soil test, and that's a rare condition, and second, if the soil is too acidic in which Case Ca++ is bound in the soil.

Again, adding lime, egg shells and on and on can not and will not prevent BER b'c absorption of Ca++ thru the roots is OK.

Paste tomatoes are especially susceptible to BER and I think someone in a post above mentioned that.

If you go to the top of this first page and click on the FAQ link and scroll down you'll also find an article about BER in case some of you have never looked at the FAQ's And there's some darn good articles there as well, but I wouldn't pay any attention to the variety list b'c it's way out of date.

The old information about BER being caused solely by lack of soil Ca++ has been shown to be wrong with research that's been done in the last 20 years or so, but it's going to take another generation before the real story gets into books, websites, magazines, etc. Most of the better websites already have the correct information.

BER affects not only tomatoes, but peppers, squash, cabbage, cauliflower, etc., and it's a huge multimillion dollar problem for the industry, which is WHY all that reasearch was done. For instance, when tissues were taken from a plant that has BER fruits and was assayed for Ca++, the normal level of Ca++ was found, it just wasn't getting to the blossom end of fruits. And there's also a condition called internal BER where the fruits look fine, no evidence of BER externally, but when you cut open the fruit the inside is black

Hope that helps

Betsy