It is very common for tomatoes to split, and there are a couple of reasons for these unsightly cracks. Split tomatoes can be caused by either moisture or heat stress.
You may find tomatoes with large cracks that form concentric circles around the stem. This splitting is caused by moisture stress, when the fruit becomes too plump too quickly and literally bursts through the skin. This typically occurs after a heavy rainfall that follows a dry spell.
Large cracks on tomatoes that radiate down from the stem are caused from heat stress. This occurs during periods of bright sunlight and temperatures above ninety degrees.
To help prevent splits from moisture or heat stress, try to maintain even moisture for the plants and provide good drainage in the soil. A thick layer of mulch over the plant’s roots will help keep the soil cool and evenly moist. Remove ripe and nearly ripe fruit after a heavy rain, before it has a chance to split.
Tomatoes that are already ripening can be allowed to finish ripening on the kitchen counter.
The splits are cosmetic only, and won’t affect the flavor of the tomatoes. As long as the fruit is harvested immediately it will still be good for eating.
Don’t let a tomato stay on the plant if it has split as it can easily be invaded by insects or develop mold in the open cracks.