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.
Blossom end rot is typically seen early in the season and often doesn't affect fruit that is set later in the summer. It is caused by a poor supply of water and calcium in the developing tomatoes.
Tomato plants that were planted out in the garden before the soil warmed up are susceptible to blossom end rot because their root systems don't develop well in cold soil. Without a good root system the plants cannot take up enough moisture and calcium for the developing fruit, resulting in blossom end rot. Blossom end rot may also be a problem after dry periods followed by heavy rains.
Mulching your tomato growing bed after the soil has warmed up is a good way to prevent blossom end rot as the mulch helps to maintain even moisture in the soil. You'll also want to keep the plants well watered during dry periods and avoid cultivating too closely to the plants as this can disturb tiny feeder roots that are close to the surface.
If you have tomatoes afflicted with blossom end rot, just remove those fruits from the plant, maintain even moisture for your plants and wait for the next set of tomatoes to ripen.
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