What is Blossom End Rot?

Blossom end rot is a common gardening problem for tomato growers. It is not caused by a pest, parasite or disease. It is a physiological disorder caused by calcium deficiency. Blossom end rot is most common in tomatoes, but also occurs in melons, green peppers, eggplant and other fruiting vegetables.

Symptoms of Blossom End Rot
In tomatoes, eggplants, melons and similar produce, the first symptom of blossom end rot is a darkened, water-soaked looking area on the bottom (blossom end) of the fruit. The spot may remain small or enlarge until it covers up to half the surface of the fruit. As the lesion grows, it will become dark and leathery in appearance. The blossom end of the fruit will flatten or become concave. Concentric rings occasionally appear, especially in tomatoes. Blossom end rot leaves the fruit susceptible to outside pathogens and the damaged area may begin to decay, giving it a black or brown color.

In peppers, the blossom end rot lesion is tan in color. It forms at the bottom of the fruit or along the sides near the blossom end. Blossom end rot is often mistaken for sunscald in peppers. Sunscald is white and generally occurs closer to the top of the pepper.

Causes of Blossom End Rot
Calcium is required for normal cell growth. When calcium is not present in large enough quantities to supply the needs of a growing fruit, the tissue begins to break down and eventually collapses. The result is blossom end rot.

There are several possible reasons for a calcium deficiency:

• Low calcium levels within the soil.
• Overcrowding of plants, causing a competition for the calcium in one area of soil.
• Poor root structure, often a result of transplanting young plants into cold, heavy soil.
• Damaged roots due to soil cultivation too close to the plant.
• Too rapid vegetative growth due to excessive amounts of nitrogen in the soil or overuse of nitrogen-based plant foods.
• Excessive moisture levels from heavy rainfall or over-watering.
• Insufficient moisture levels due to lack of rain and under-watering.

Moisture levels are most often the culprit in calcium deficiency and blossom end rot. Excess water absorbed by a plant is rushed to the leaves for faster removal from the system. As a result, the calcium contained in the water ends up in the leaves instead of the fruit, causing a deficiency. In times of drought, not enough water is absorbed by the plant to pull in the needed calcium.

Prevention of Blossom End Rot
It is easier to prevent blossom end rot than to correct the problem once it begins.

Garden site - Choose a garden site that has deep, well-drained soil. Transplant young plants only after the soil has had a chance to warm and dry out after the spring thaw. Provide proper spacing between plants, extending your garden space when needed.

Moisture - Avoid extreme fluctuations in moisture levels. Tomato plants require 1 inch to 1.5 inches of water per week, through either rainfall or watering. Do not waterlog your plants when watering. Use soaker hoses or other forms of irrigation to keep the water supply steady during times of drought.

Mulch plants using natural materials to conserve and balance moisture. Surrounding plants with plastic will increase the risk of blossom end rot during times of drought, as the material holds in too much heat. Be sure to water properly if you choose to use plastic.

pH balance - Prepare soil at least 2 to 3 months in advance of planting. Have your soil tested by professionals or buy a home testing kit from your local garden shop. For best blossom end rot prevention, tomatoes and other susceptible plants need soil with a pH between 6.0 and 6.5. Adding lime to acidic soil with bring it into proper pH balance. If your soil has not had lime added within the last 2 or 3 years, work 2 cups of lime per plant into the soil to a depth of 12 inches.

Fertilization - Use a home soil testing kit from your local garden shop to test the nitrogen level of your soil or send a sample to soil testing professionals in your area. A good test kit will include instructions on how to adjust the nitrogen level, if needed.

For soil that has not been tested, mix 1/2 cup of lime, 1/2 cup of bone meal and 2/3 cup of 6-12-12 or 5-10-15 plant fertilizer for each plant and mix it into a 2 X 2 area to a depth of 12 inches.

When feeding your plants, use a low nitrogen fertilizer that is high in superphosphate. A good mixture is 4-12-4 or 5-20-5.

All the above mentioned soil amendments, as well as a home soil testing kit, can be found at your local garden shop or in the garden centers of hardware stores (Home Depot, Lowes) and discount stores (Walmart, Kmart).

If you have taken precautions and still notice blossom end rot forming on your tomatoes and other garden produce, increase the calcium levels of your soil by mixing such things as powdered milk, crushed eggshells, or bone meal into the soil around your plants. Work them into the soil as deeply as possible without damaging any of the plant root system.

Calcium sprays are available, but can be poisonous to plants if used incorrectly. Always follow the directions on the package. Gardens Alive!, known for environmentally safe products, offers a spray called Enz-Rot, which is designed to restore calcium and prevent blossom end rot.

Sources:
The University of Georgia College of Agricultural & Environmental Sciences
Cornell University Dept. of Plant Pathology
Department of Horticultural Science, North Carolina State University