Tomatoes split or crack because of changes in its growing conditions. A rapid increase in moisture causes tomatoes to expand faster than the skin can grow. Hot, dry weather, combined with irregular watering, is a common cause of tomatoes splitting on the vine. Splitting is most common in late summer.
Tomatoes are still edible if the skin has split. Cracked skin is not a sign of bugs or pests; however, tomatoes can rot quickly once the skin has split. Cracks that run lengthwise, known as radial splitting, are the most serious. Tomatoes with such cracks should be picked immediately and allowed to finish ripening indoors.