Blossom End Rot on Tomatoes

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Q: Why are the bottoms of my tomatoes rotting?

 A:        It is that time of year that the tomatoes should be soon starting to turn red and gardeners are eagerly awaiting that first fresh tomato out of the garden. Unfortunately, a common problem that occurs for many home gardeners is to have tomatoes turn brown on the bottom right before it begins to ripen. When this spot is noticed it is often thought that a disease is causing the rot to occur, but in fact what is occurring is referred to as blossom-end rot on tomatoes. Blossom-end rot is not a disease but instead is a nutrient deficiency. The nutrient that is lacking is calcium.

Blossom-end rot will be a rot that is dark brown in color and has a tough, leathery feel. The rot will be on the blossom-end of the tomato fruit. The spot is usually about the size of a dime and enlarges to the size of a half-dollar. Typically, blossom-end rot is worse on the first fruit that develops but it can also occur throughout the season.

As mentioned previously, blossom-end rot is due to a lack of calcium in the fruit. There are a couple of things that can cause calcium to be deficient in the tomato. One way is if soil pH is too low which would cause calcium to not be available to the plant.

Dry weather or improper watering practices can also contribute to a calcium deficiency in the tomato fruit. Tomatoes require about 1 inch of water per week. Extreme fluctuations in soil moisture (either too dry or too wet) result in a greater incidence of blossom-end rot. Inconsistent soil moisture is often the main contributor to blossom-end rot.

Of course the question is, what can be done to prevent or correct blossom-end rot. As far as correcting goes, the tomatoes that are already affected will continue to be deformed. They are safe to eat, but it reduces the amount of the tomato that can be used. If you have a lot of tomato plants with blossom-end rot, it might be good to pick off and get rid of the fruits that are severely affected.

When blossom-end rot is first spotted, spraying a calcium solution (Tomato Saver, Blossom-end Rot Preventer, Stop Rot) will help reduce blossom-end rot on later tomatoes. Ideally, calcium spray should start when the first green tomatoes are about the size of a silver dollar. Check the label for how much and how often you should spray.

If blossom-end rot is a recurring problem each year, you should get a soil test to see what the soil pH is. If the soil pH is too low, calcium is not available to the plant. Optimum soil pH for tomatoes should be 6.5 to 6.7. Adding lime to the soil will increase the soil pH and add calcium to the soil. Getting a soil test will be to only way to determine for sure what your soil pH is and how much lime you should add. Soil test kits are available at Wayne County Extension Office.

Proper watering and fertilizing practices are important in reducing blossom-end rot. Mulching around plants will conserve soil moisture and reduce moisture fluctuations in the soil. Avoid applying too much fertilizer at one time and avoid high rates of nitrogen fertilizer.

Following these practices can reduce the chances of discovering blossom-end rot on your tomatoes and instead will allow you to enjoy that fresh home-grown tomato!

Recommendations for the use of agricultural chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this article does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.

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Jessica Strickland is an Agriculture Extension Agent, specializing in horticulture for North Carolina Cooperative Extension in Wayne County. Horticulture program information can be found at // Forward any questions you would like answered from this week’s column to