Blossom-end rot is physiological condition caused by calcium deficiency in the blossom end of the fruit. It occurs most notably in tomatoes, but also occurs in peppers, squash, watermelon and any other fruiting vegetable. It is characterized by the decay of fruits at their blossom end; appearing as a dry brown spot about the size of a dime, that may blacken and sink in as it grows to about the size of a half dollar. This disorder is most severe following extremes of over or under-watering.
There are steps that can be taken to greatly reduce this condition:
- Lime soils to a pH of 6.5 to 6.7 before planting. Gardens not limed within the past 2-3 years will need 2 cups of lime per plant. The lime should be worked in to a depth of 12 inches.
- Fertilize properly. Applying too much fertilizer at a time can result in blossom-end rot. Following soil test recommendations is the best way to ensure proper fertilization. Terracycle makes a Tomato Plant Food based in worm poop that has a calcium boost. I have found it to be very effective.
- Mulch plants. Use straw, pine straw, decomposed sawdust, plastic or newspapers. Mulches conserve moisture and reduces blossom-end rot.
- Water when necessary. Tomato plants need 1-1.5 inches of water per week during fruiting. Extreme fluctuations in soil moisture can increase blossom-end rot.
- Spray calcium. Plants may be sprayed with a calcium solution at the rate of 4 level Tbs of calcium nitrate or calcium chloride per gallon of water. The spray should be applied 2-3 times per week, beginning when the second fruit clusters bloom. Several foliar sprays containing calcium are available and all work well for tomatoes. Calcium chloride is only suggested for tomatoes.
- Quick fixes. Foliar application of a weak Epsom Salt (magnesium) solution can effect calcium uptake. Other suggestions include powdered milk, crushed egg shell tea, bone meal tea, Tums tablets, etc., but prevention is the key. Removing affected fruit is also recommended to reduce stress on the plant. "Gardens Alive" sells a product called Rot-StopT Spray that can be applied to plants weekly to supplement calcium reserves and prevent rotting.