I was out of town Wednesday night and came home to three inches of rain in the rain gauge and a handful of cracked tomatoes. The two items are related.
Why Tomatoes Crack: To grow well and fruit profusely, tomatoes need even, consistent moisture. I water tomato plants during dry periods to encourage fruiting and healthy growth. But when Mother Nature dumps a bucket of moisture on the ground, the plant naturally takes it up and the fruits crack. Their skins can’t grow fast enough to take in the extra moisture. Cracking is most common with a heavy rain after a long dry spell, though this was not the case here because we have had an unusually rainy August. As typically happens, the fruits closest to ripeness cracked. The cracks in the fruits provide an entry point for bacteria and fungi, and typically the fruit will rot quickly—in fact, I tossed one really rotten tomato before taking the picture.
Can you prevent cracking? You can’t prevent cracking from extreme storms, but you can prevent losing tomatoes due to cracking, by harvesting tomatoes most susceptible to cracking. Green or very unripe tomatoes are less likely to crack, so picking those that are ripe or nearly so before a big storm is a good way to prevent cracking. Since I was away during the last storm, I picked a lot of ripe or nearly ripe fruit right after I got home. You can prevent cracking if the problem is dryness by watering regularly. You also can reduce cracking by growing tomatoes in raised beds, which drain more thoroughly than in-ground gardens, and by applying a layer of compost or other mulch to keep soil evenly moist in dry periods.
Are there tomatoes that don’t crack? Yes, there are some varieties that resist cracking. (Those that crack the most tend to be heirloom varieties and large tomatoes.) You can find a long list here of crack-resistant varieties. Popular varieties that crack less include Arkansas Traveler, Celebrity, Big Boy, Big Beef, Summer Sweet, Sungold and Yellow Pear. If cracking tends to be a problem with your tomatoes, you may want to choose a crack-resistant type.
What about calcium and cracking? Calcium helps tomatoes regulate their intake of moisture, and a shortage of calcium in the soil is also linked to blossom end rot, another really discouraging tomato problem. Some gardeners add crushed eggshells to the planting hole, antacid tablets or a commercial calcium to increase the calcium available to plants. Consider a soil test before you heavily supplement the soil.
We have more rain in the forecast for the next couple of days, so I will be harvesting more tomatoes today. How are your tomatoes doing during this rainy period?