My tomatoe plants have lovely tomatoes (pear type) and as they start to ripen, they get black on the bottom, and by the time they are ripe, half of the tomatoe is black on the bottom.

It's called blossom end rot, and is fairly common at the beginning of the garden season, but not usually a problem by this point. I've heard and read various causes with the primary ones being inconsistent watering, and the other being a lack of available calcium in the soil. Are your plants in containers or in the ground. This problem seems more prevalent in container tomatoes.

In reading thru the posts regarding tomatoes, what is simple to add to soil to increase calcium, just as cornmeal is simple to add to provide phosphorus? I have container tomatoes and they are flowering.

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Tender of my Garden

This came up last year also. Soft Rock Phosphate may be your answer. See the posts below.

http://www.dirtdoctor.com/forum/viewtopic.php?t=3905&highlight=phosphate

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The "soap" you use is normally chemicals, etc. Use real SOAP !!

Over on GW they say too high N content in the soil causes this problem as well. I have no studies to link to back this up.