Both green and ripening tomatoes can develop cracks from the stem outward across the top of the tomato. Splitting of the tomato skin can result from inconsistent watering such as periods of dryness followed by an abundance of moisture. Rather than using a regular watering schedule (like every seven to 10 days), test the soil’s moisture by sticking your finger into the soil near the base of the tomato plant or use a water moisture gauge. Water only until the soil is moist, not saturated. Help to keep the soil moist by spreading 2 to 4 inches of mulch around the tomato plant.
Split top tomatoes are still good to eat. Just cut off the split area.