Avoiding Blossom End Rot

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Tomatoes with blossom end rot

Tomatoes with blossom end rot

It’s been a wet spring. In fact, as I write this article, we’ve had 8.5” of rain in the past week. The seemingly daily showers have caused some issues in gardens, including fruit cracking, disease spread, yellowing plants, and blossom end rot.

Blossom end rot is one of the most common problems of tomatoes. It is characterized by a brown or black leathery spot on the bottom (the blossom end) of crops. Sometimes mold will colonize the area, and it will be fuzzy. Blossom end rot is most common on tomatoes and squash, but also affects peppers, eggplants, melons, and cucumbers.

Blossom end rot is not a disease but a disorder, so it won’t spread from one plant to another. The sunken dark area of rot is due to a calcium deficiency in one end of the fruit. Without enough calcium, cells collapse, and tissue rots.

Plants absorb calcium (and other nutrients) from soil. While blossom end rot can be caused by a lack of calcium in soil, this is typically not the case. Instead, we see blossom end rot appear during extreme weather, which stresses plants and interferes with water uptake. Sometimes just the first fruit from a plant will have blossom end rot, and it won’t be a problem on fruit harvested later in the season.

The disorder is most often caused by excessively wet or dry weather, several days of hot temperatures, or low soil pH. All of these conditions reduce a plant’s ability to absorb nutrients, including calcium.

To prevent blossom end rot, keep soil evenly moist. Don’t let it dry out and then soak it. During the growing season, plants need an inch to an inch and a half of water per week. (Of course, there’s not much you can do when it rains an inch every day.) Soaker hoses are the preferred method of watering, because they put the water at the roots, where it is needed. A two- to three-inch layer of mulch, like straw, will also help to keep soil moisture consistent.

A pH that is too low will decrease the amount of calcium a plant will take up. The ideal soil pH of a garden is between 6 and 6.5. To determine if the pH of your soil is too low, submit a free soil sample to the North Carolina Department of Agriculture. Kits are available at the Caldwell Extension office.

If the soil test report recommends increasing the soil pH, lime should be tilled into the soil to a depth of 6 to 8 inches. Lime is slow acting, often taking months to change soil pH, so it’s unlikely that it will affect this year’s garden.

Another common cause of blossom end rot is over-fertilization. Too much nitrogen fertilizer causes plants to grow quickly, and they often cannot move enough calcium to the fruit, so the fruit doesn’t develop properly. Avoid over-fertilizing by following the recommendations from your soil test report and using slow-release or organic fertilizers.

Root damage of any kind can also increase the incidence of blossom end rot. Roots can be damaged by extended periods of wet soil and by cultivating too close to plants (1’ is close enough).

While blossom end rot is a common disorder, it can be avoided by following these steps. For more information on blossom end rot, visit http://go.ncsu.edu/ber