Some tomato fruit are cracking now that we’re in the midst of tomato ripening season. Stem end cracks can be of two kinds but are both due to the same causes. You may see cracks that spread outward from the stem (radial cracks see photo right) or concentric cracks in circles with the stem in the center (photo left).
Cracks generally appear as fruit is maturing (mature green or coloring), rarely when small. The earlier fruit cracks, the deeper cracks become.
Growth cracks can be traced to rapid changes in environmental conditions, either moisture, temperature or both acting together. Dry weather followed by heavy rains is known to cause cracking in many tomato varieties. The strength and ability of the skin to stretch vary by variety and thus some varieties are marketed as “crack resistant.” They are worth a try if you have had problems.
High nitrogen fertilization stimulating rapid growth is also a cause for cracking. Slow release granules, organic sources or low strength fertilizers (soluble types in water) should be considered for fertilizing now.
Cherry type tomatoes are problematic for growth cracking. They are so small that when cracks occur they often run down most of the fruit (photo right - click to enlarge). Harvesting fruit before it turns dead ripe eliminates the possibility that further growth on the vine will result in cracks.
Do everything you can to even out the water to avoid growth cracks; irrigate not too much and not too little. Mulch soil to prevent rapid summer evaporation and dry down. The cherry tomatoes pictured are growing in a large container where it is always difficult to maintain even moisture in spite of daily watering.
Although gardeners can modify fertilization and watering practices, they can’t change the temperature. Temperature fluctuations and our dry air that toughens skins are probably big reasons we have cracking problems. Our average day-night temperature fluctuation for August has been 29 degrees F. That’s a wide range of temperature for a plant to handle.
Photo credit: Radial cracking - Carl Wilson, Concentric cracking - Iowa State University Extension, Cherry tomato fruit radial cracking - Carl Wilson