3 Answers

Tomatoes tend to crack when they receive irregular water. If your tomatoes have gone through a dry spell and you try to make up for it with frequent waterings, the inside of the tomato will plump up faster than the outside can stretch and grow. As a result the outer skin of the tomato splits open or cracks.

Tomatoes that crack are still edible. They just won't keep as long. You can prevent future tomatoes cracking by making sure that they receive water regularly, whether or not it rains. Mulching the area around the tomatoes will also help maintain ground moisture levels. Finally, look for varieties that are resistant to cracking.

Splitting or cracking can be quite common and is brought about by fluctuations in watering. This can be due to heavy watering after a long period of no water. It can also be caused by having a period of dry weather, then getting a heavy rain that suddenly over-waters the tomatoes. Splitting and cracking is most prevalent in the later stages of growth when it is beginning to ripen.
When it begins to ripen during a spell without water, the outer skin will thicken and toughen up. A sudden influx of water will cause the tomato to swell (or continue growing) on the inside. This inner swelling will then cause the thickened outer skin to rupture resulting in a split or crack. Although some minor cracking at the top of the tomato is generally harmless, large splits that expose the tomato flesh can invite disease and insect pests.

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