Blossom-end rot is a troublesome condition caused by calcium deficiency. It’s easily identifiable as a soggy patch on the bottom (blossom end) of the fruit, which grows into a sunken, round, brownish or black area that soon becomes leathery and moldy. Blossom end rot affects primarily calcium-loving vegetables such as tomatoes, peppers, and eggplant.

Blossom-end rot becomes a common problem when we over fertilize our young plants, then subject them to hot summer drought and inadequate watering. Between the drought, the flush of growth, and the overload of competing nutrients, calcium doesn’t stand a chance of getting properly absorbed by the plant. While some soils are actually deficient in calcium, more often we’ve created conditions that prevent the plant from absorbing it.

This condition is not caused by bacteria or fungus, it’s not contagious, and it doesn’t kill the plant, so there’s hope for recovery. Remove and discard only the affected fruits, and focus on getting your plant healthy. Here’s how to prevent and treat blossom end rot:

• The most important defense against blossom end rot is keeping your plants evenly watered! Make sure they get an inch of water per week and that they are not subjected to extremes of drought or soaking.
• Use mulch to even out soil moisture.
• Avoid overfeeding with chemical fertilizers as well as excess nitrogen. Use natural compost tea or balanced organic fertilizers instead.
• Plant tomatoes, peppers, and eggplant in high-quality soil with plenty of organic matter. Some gardeners add a spoonful of lime, a handful of crushed eggshells, or other calcium supplement to the planting hole as a preventative measure.
• Do a soil test to determine if your soil is deficient in calcium. Follow the recommendations of the soil test to correctly balance your soil.
• In an emergency, you can purchase calcium sprays that are applied directly to the foliage and can help get your plants back on track. In general, though, you’re better off preventing the problem through proper plant care.

Further Information

• Blossom-End Rot of Tomatoes (Oregon State)
• Blossom-End Rot of Tomato (Integrated Pest Management)
• Blossom End Rot of Tomatoes and Other Vegetables (South Dakota Extension)