Tomato Plants and the Heat

Tomato Plants and the Heat

by Dotty Woodson

The hot summer temperature causes several problems for tomato plants. Blossom end rot, spider mites and no new fruit are problems for tomatoes during hot temperature days. During normal summers, these problems do not become severe until July.

On tomatoes, blossom-end rot begins as a light-colored area on the blossom end of the fruit (opposite from the stem). The affected area enlarges and darkens, sometimes involving up to half the fruit surface. On peppers, the rot is tan on the lobes of the fruit and may be mistaken for sun scald. Sun scald actually results in a bleached, white area on the fruit.

Blossom end rot is a water issue. Tomatoes grow so fast once the fruit start to develop. During the expansion of the fruit, if there is a lack of water in the soil blossom end rot occurs. Physiologically, blossom end rot is caused by lack of calcium. As roots absorb water, the nutrients plants require enter with the water. If there is a lack of water then there is a lack of calcium. The soil and water in this area have plenty of calcium so unless the tomato is growing in an artificial medium the addition of calcium is not usually necessary. To prevent blossom end rot, keep the soil evenly moist, not wet. The only way to accomplish even moisture is to water thoroughly and cover the soil with a thick layer of mulch. About 4 inches of mulch from near the base out to the drip line of the tomato should help prevent this problem. The mulch keeps the water from evaporating from the soil and moderates the soil temperature. Blossom end rot also may affect peppers, eggplant and squash.

Spider mites like tomatoes and the heat. Spider mites are tiny arachnids (spiders) that like to suck the carbohydrates out of the tomato plant leaves. Spider mites are found on the underside of the leaves because these spiders want protection from the sun and rain. The damage looks like mottling on the leaves, tiny yellow and green pattern. The sucking process removes the chlorophyll. As the spider mite population increases, the edge of the leaves will become dry and curl. Control spider mites by knocking the mites off with water by giving the tomato plant an upside down shower. Start at the bottom and wash the bottom of the leaves off daily until you have some control. The water knocks off the mites and creates an unpleasant condition for the mites because spider mites do not like water. Or use as insecticide labeled for mites on tomatoes. Insecticidal soap and plant oils work great. Remember apply these products under the leaves.

Unfortunately, once the temperature remains above 95 degrees, tomato plants will flower but not set fruit. Tomato plants are wind pollinated. If there is no wind, shake the plant or flick the flowers lightly with a figure. Since the night temperature is dropping to 80 degrees, I do not think we will see this affect right way. We usually do not see this effect until mid to late July which is when we recommend planting fall heat tolerant tomatoes.

Do not allow these problems discourage you from planting tomatoes. Plant tomato plants as early in March as possible to enjoy the wonderful taste of home grown tomatoes before these problems become severe. Plant fall tomatoes, mid to late July.

If you have any questions, email me at