Many homeowners have been impatiently waiting for those first ripe tomatoes, and are disappointed when their first tomatoes have dry sunken areas of decay on the blossom end of the fruit. This is the primary symptom of a tomato disorder called blossom-end rot. Blossom-end rot has been very prevalent this year and has been very damaging to tomatoes. Fortunately, blossom-end rot is most common in the first fruits of the season. Blossom-end rot usually begins as a small water-soaked area at the blossom end of the fruit. This may appear while the fruit is green or during ripening. As this lesion develops, it enlarges, becomes sunken and turns black and leathery. In severe cases, the entire lower half of the fruit may become flat or concave. Decay bacteria often invade this lesion resulting in rotting of the fruit. Blossom-end rot is not a disease, but is a physiological disorder associated with a low concentration of calcium in the fruit. Calcium is required in relatively large concentrations for normal cell growth. When a rapidly growing fruit is deprived of necessary calcium, the tissue breaks down, leaving the characteristic dry, sunken lesion at the blossom end. It is normally not caused by a lack of calcium in the soil, but by some factor that makes the calcium unavailable to the plant. These factors include drought stress, fluctuations in moisture and temperature, heavy applications of nitrogen fertilizer, and root pruning caused by cultivation. Blossom-end rot is common this year because of the stress caused by erratic and unseasonable temperatures. Maintaining a uniform supply of moisture through regular watering and mulches can minimize blossom-end rot. Plants generally need one inch of moisture per week for proper growth and development and it is important that the soil does not become excessively dry between waterings. Two to three inches of organic mulch will help keep the soil temperature and moisture level uniform. Avoid heavy applications of nitrogen fertilizer as rapid and luxuriant growth predisposes the fruit to blossom-end rot, especially during periods of dry, hot weather. Ammonium-based nitrogen may increase blossom-end rot as excess ammonium ions reduce calcium uptake. Avoid root pruning caused by deep cultivation within a foot of the plants. The soil around tomato plants should never be hoed or cultivated deeper than one inch to avoid root injury. Container-grown tomatoes are especially susceptible to stress that will result in blossom-end rot. The root restrictions induced by the smaller amount of soil available make them vulnerable to stress caused by rapid changes of soil temperature and moisture. Diligent watering and the application of mulch on the surface of the soil will help maintain more even levels of moisture and temperature.
