Blossom-end rot is technically a physiological disorder brought on by a calcium deficiency in the young fruit, Goodspeed explains. Although it is a calcium problem, it is mostly related to water imbalances and stress in the plant. Blossom-end rot can be a problem when the weather is hot and something interferes with the plant's ability to take up and move calcium into the fruit. Problems arise when the roots are damaged or there are excessive salts in the soil, which can include an over-abundance of fertilizer, he says. Hot weather increases the incidence of BER, as well as fluctuations in the water.
Some varieties are also more susceptible than others.
Controlling BER can be as simple as reducing the watering frequency, Goodspeed says. Do not over-water tomatoes, especially in clay and heavy soils. A good mulch around the plant helps reduce water loss due to evaporation and keeps the moisture level a bit more consistent around the roots. Water deeply and infrequently. Another cultural practice that helps reduce the likelihood of BRE is avoiding over-fertilization, he adds.