Posted: 02/09/2012 at 07:24
Some varieties, particularly cherries, are prone to splitting. They have very thin skins. Sungold F1 is a famous example. Beyond that, splitting is usually related to excess moisture. It will often happen after sudden heavy rain. In simple terms, the sudden excess of moisture causes a growth spurt in the tomato but its skin is unprepared for it. Something has to give, and it's the skin. It's like putting on a tight pair of jeans, breathing out, and popping the top button. I speak from experience.
Simple overwatering can also cause it.