What's with the ugly tomatoes?

The long-awaited tomato harvest has begun. Tomatoes are ripening, but what's with the blackened leathery spot on the bottom? We put in all kinds of time and energy to grow lovely, delicious tomatoes and these are ugly.

The problem is blossom end rot (BER), a physiological issue. It's not a disease, so the unaffected parts of the tomato are still edible, once you cut away the blackened part. BER can also affect peppers and eggplant, although the discoloration may be a little different in them.

This fruit disorder is directly related to soil moisture and soil calcium. BER is common when plants grow rapidly early in the season. It is exasperated by windy, dry weather. 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.

BER is often attributed to calcium deficiency with addition of lime a recommended solution. Nevada soils are high in calcium and adding lime is not the answer. Lime makes a soil more alkaline and since most Nevada soils are too alkaline to begin with, this is not a good idea. Foliar applications of calcium are of little value. Another possible factor in BER is hoeing too closely. This can damage or cut shallow feeder roots preventing them from adequate moisture absorption.

What's a gardener to do? Maintain a soil pH of 6.3 to 7. Keep plants evenly watered from planting to harvest. This means avoid overwatering early in the season when soils are still cool, and avoid underwatering later as the weather heats up. As it gets hotter, mulch about two feet around the plant to conserve soil moisture. Mulching too early will keep soils too cold for good root development. Over-fertilizing can increase BER, particularly with high nitrogen fertilizers, because this causes rapid vegetative growth. Slow release or organic fertilizers are good options.

Some varieties are more prone to BER than others are. Plant indeterminate or semi-indeterminate varieties rather than determinant bush varieties. Indeterminate types grow fruit over the whole season while determinate types produce many fruit late in the season. The flush of fruit production is hard on nutrient uptake.

Keep your tomatoes happy and irrigate efficiently.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu


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