There are two different types of splitting (cracking) that occur on tomatoes − radial and concentric. Radial cracks go down the sides, while concentric (circles) go around the stems. Both occur when fruits expand rapidly. Usually, rapid intake of water is responsible for the cracks. Once fruits get full sized, the skin and flesh of the fruit lose their elasticity. And when water gets moved into the fruits, they crack. Varieties vary in their susceptibility to cracking. Most heirloom varieties are prone to cracking, while the newer hybrids are more resistant. To reduce cracking, maintain more uniform watering (don't go from wet to dry to wet) and don't over fertilize the crop. Too much fertilizer causes soft growth and those plants produce fruits more prone to cracking.