JoAnne Skelly: What’s wrong with my tomatoes?

You might be noticing issues with your precious tomatoes such as blackened leathery spots on the bottom, cracks on top or catfacing. Gardeners work hard to grow delicious tomatoes and when the fruits aren’t thriving, they worry.

The blackened bottom is called blossom end rot (BER). It’s not a disease, so, although ugly, the unaffected parts of the tomato are still edible; just cut away the blackened part. This fruit disorder is directly related to soil moisture and the delivery of soil calcium in that soil water. BER is common when plants grow rapidly early in the season. It is exacerbated by windy, dry weather (oh, that never happens here!). As plants grow, they need more water, especially while the fruits are developing. If soils get too dry or too wet, roots can’t absorb the water or nutrients they need, and plants can’t grow properly. Moisture fluctuations reduce calcium uptake.

The addition of lime is often recommended for BER. Since Nevada soils are already high in calcium, adding lime (calcium carbonate) is not the answer. Lime makes a soil more alkaline and most Nevada soils are too alkaline to begin with. Foliar applications of calcium are of little value. Hoeing too close to the plants could contribute to BER because it can damage or cut shallow feeder roots preventing them from absorbing adequate moisture.

Cracks and splits on the top of a tomato are also due to rapid or extreme changes in soil moisture. This causes the fruits to expand more quickly than the tomato skin can grow. It also can occur when there have been wide differences in temperatures from day to night. When cracking occurs in green tomatoes, fruits are likely to rot before they fully ripen. Harvest fruits immediately, before they begin to rot and let them ripen indoors. Although unsightly, fruits are edible.

Catfacing disorder is where the fruit is deformed and distorted particularly on the blossom end. It might look like a cat’s face. There might be dark scar tissue, possibly with holes in it. It can be caused by cold weather (below 52 degrees) during early stages of growth and blossoming, by extreme fluctuations in day to night temperatures, or even by extreme heat during growth and ripening. Excessive nitrogen can increase this problem.
Keep plants evenly watered from planting to harvest. Avoid underwatering. Mulch 2 feet around the plant to conserve soil moisture. Use slow-release or organic fertilizers.

JoAnne Skelly is associate professor and Extension educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.