Blossom end rot a common, but preventable, problem

There is nothing quite like a tomato sandwich in the middle of summer. Just the thought is making my mouth water. The work that goes into getting the tomato to that point makes this treat even sweeter. If you have ever grown tomatoes before, you are aware of the challenges one must overcome to pick that big, juicy tomato. One of the most common problems that occurs is blossom end rot. The bottom end of the tomato turns black in color and leathery.

Blossom end rot occurs on tomatoes and other garden vegetables such as peppers, eggplants, melons, cucumbers, and squash. It is not a disease and it does not spread from one plant to another. Instead, it is classified as a plant disorder and is caused by a lack of calcium in the developing fruit. It is very common for the first fruit that develop on a tomato plant to have blossom end rot, but for all tomatoes that develop during the rest of the season to be normal. In other cases, gardeners may lose 50% or more of their season’s harvest to this problem. There are several factors that can lead to calcium deficiency in tomato plants, all of which must be managed to prevent blossom end rot from developing at anytime during the harvest season.

Another common cause of blossom end rot is over fertilization with high nitrogen fertilizers. Nitrogen promotes rapid, dark green, leafy growth. Plants that are growing very quickly often cannot absorb enough calcium through their roots to supply the needs of the rest of the plant, leading to blossom end rot developing in the fruits of rapidly growing plants. In addition, any conditions that cause root damage will lead to poor nutrient absorption and blossom end rot. The most common causes of root damage in vegetable gardens are wet soils following heavy rainfall and hoeing too close to a plant’s root system.

Preventing blossom end rot relies on testing your soil to make sure calcium and other nutrient levels are adequate and your pH is in the correct range of 6.0 to 6.5, as well as managing growing conditions to maintain even growth of your tomato plants through careful fertilization and watering. Soils can be tested anytime of the year to determine pH and nutrient content. In North Carolina, soil testing is a free service provided by the North Carolina Department of Agriculture. If your tomatoes are developing blossom end rot, take a soil sample and send to the soil testing lab in Raleigh. They will test soil samples free of charge from April through November. Soil sample kits can be picked up at your local NC Cooperative Extension Center. Results will be e-mailed to you within a few weeks. The recommendations made in the results should be followed when preparing your garden next season, to help prevent blossom end rot developing on your tomatoes next year.

To prevent blossom end rot on tomatoes growing this year, keep plants evenly moist by watering during dry weather and mulching around plants. Tomatoes require between an inch and an inch-and-a-half of water each week from rainfall or irrigation to grow best. When rainfall is lacking, water tomato plants once or twice a week in the garden. Soaker hoses are wonderful for watering tomato bushes and other plants because they apply water directly to the ground, instead of wetting plant leaves, which can make disease problems worse. Also, do not use high nitrogen fertilizers, in which the first number on the bag is higher than the rest of the numbers. Instead base fertilizer applications on your soil test results using a fertilizer that has more potassium (represented by the last number on the bag) than nitrogen, such as 5-5-15. Applying lime to the soil to raise the pH and supply calcium will not help this year’s crop because lime takes several months to react in the soil. In addition, lime must be tilled into the soil 6” to 8” deep to provide much benefit, and is best tilled in at least three months before planting. The same is true for gypsum, sometimes referred to as land plaster, a substance that supplies calcium without raising soil pH.

Liquid calcium sprays are available to spray onto tomato plant leaves to prevent blossom end rot. These sprays will not fix the damage done to already developed fruits, but should prevent future fruit from developing blossom end rot. Liquid calcium sprays are sold under names such as Rot Stop and Blossom End Rot Spray. They should be sprayed onto the leaves of tomato plants in the early morning or late afternoon once every five to seven days over the course of three to four weeks. Continuous application of these sprays can damage plant leaves so they should not be used for over four weeks. Applying these sprays on tomato fruits will provide no benefit since nutrients cannot be absorbed through the skin of developing fruits. Read and follow all label directions when using these products.

By following these tips, you should have your tomato sandwich to enjoy this summer. Good luck to you and may you have enough tomatoes to share with others to help brighten their day.