A. Cracking is caused by fluctuations in soil moisture, caused by uneven or infrequent watering – particularly after the fruit has reached the mature green stage and is beginning to ripen. At this stage of growth the skin becomes thicker and more rigid. When the water supply is then restored, the plant will resume bringing nutrients and moisture into the fruit. This will cause the fruit to enlarge, which in turn splits the skin and results in cracking.
Some people believe you shouldn’t water after the fruit begins to ripen, and if you want only those few fruits that are already grown, then you can perhaps ripen a few tomatoes without additional water.
However, indeterminate tomatoes will produce fruit for MANY months, until frost kills the plant, so stopping the water permanently is not a good solution – for cracking or anything else.
The single best control for cracking is a constant water supply to the root zone of the plants. This requires watering daily – and sometimes even more often in very hot weather.