Blossom-end rot of tomatoes is a physiological disorder caused by a lack of sufficient calcium in the blossom end of the fruit. This disorder results in the decay of tomato fruits on their blossom end. Dry brown or tan areas the size of a dime, that grow to the size of a half dollar, characterize this disorder.
This disorder is usually the most severe following extremes in soil moisture (either too dry or too wet).
To reduce blossom–end rot in tomato, implement the following steps:
1. Lime tomato soils to pH 6.5 to 6.7. Home gardens not limed in the past 2-3 years will need two cups of dolomitic lime for each plant. The lime should be worked into the soil 12 inches deep. To determine the exact amount of lime, see your county Cooperative Extension Service for soil testing information.
2. Fertilize properly. Applying too much fertilizer at one time can result in blossom-end rot. For home gardens not soil tested, apply 5 pints of 8-8-8 per 100 feet of row and thoroughly work into the top 8 inches of soil.
3. Mulch plants. Use pine straw, wheat straw, decomposed sawdust, plastic, newspaper, or composted leaves.
4. Irrigate when needed. Tomato plants require 1.5 inches of water per week during fruiting. Extreme fluctuations in soil temperature can result in a greater incidence of blossom-end rot.
5. Spray calcium. Plants may be sprayed with calcium solution at the rate of 4 pounds of calcium nitrate or calcium chloride per 100 gallons of water (or four level tablespoons per gallon of water of water). This spray should be applied two or three times a week, beginning at the time the second fruit clusters bloom. Chelated calcium solutions also provide an excellent source of calcium.
Story prepared by Doug Sanders, N.C. State Extension horticultural specialist.