Dry rot, also known as blossom end rot, is a condition that rots away the fruit on tomato plants. The disease is connected to the plant's supplies of moisture and calcium. Tomato plants that are irregularly watered often develop the condition, as do those that are planted in nutrient-sapped soil. Treating dry rot can be difficult, as it often requires helping the soil recover from the unfavorable circumstances that caused the issue in the first place.
Pluck off and discard all of the rotten fruit. Though the condition cannot spread to healthy tomatoes from rotten ones, it's best that the tomato plant not expend any more energy developing these fruit.
Straighten out the tomato plant's watering schedule. Tomato plants should be watered once daily, preferably in the early morning. The soil should be soaked thoroughly, but no standing water should remain on the surface of the dirt.
Apply a fertilizer that's designed for tomato plants, following the instructions on the packaging. Generally speaking, the most effective choice is one that is low in nitrogen, but high in superphosphate (such as 4-12-4 or 5-20-5).
Spray the plant with a calcium chloride solution to treat extreme cases of dry rot. However, know that this spray can be toxic to the plant when it's applied in large amounts. For best results, follow the directions on the packaging or consult a professional at your local garden center to determine the amount needed for your tomato variety.
Spread a 1- to 2-inch-thick layer of mulch on top of the soil surrounding the plant. This will help lock in moisture and prevent further incidents.