Blossom-End Rot in Tomatoes


Ag Biz News Column
By:  Chad Gulley
County Extension Agent—Ag/NR
Smith County


Blossom-End Rot of Tomatoes

It is that time of year when many gardeners are beginning to harvest the fruits of their labor.  It can also be a stressful time because of the many insect and disease problems that we may have to deal with. It is very frustrating when we reach for that tomato that we have been watching develop and realize that it is rotten on the bottom. Blossom-end rot is a major problem for many home gardeners. There are several things we can do to reduce or prevent the problems of blossom-end rot.

Blossom-end rot of tomatoes is a physiological disorder caused by a lack of sufficient calcium in the blossom end of the fruit usually induces by water stress. This problem results in the decay of tomato fruits on the blossom-end. This disorder is usually most severe following extremes in soil moisture.  Blossom-end rot is a physiological disorder, not a disease.

To reduce the incidence of blossom-end rot in tomatoes, implement the following steps. Check the pH of your garden soil. The ideal pH of a garden soil should be 6.5 to 7.  Home gardens not limed in the past 2 to 3 years could probably benefit from an application of lime.  To determine the exact amount of lime, send a soil sample to one the soil testing labs and apply lime according to the soil test recommendations.

Applying too much fertilizer at one time can result in blossom-end rot.  Following soil test recommendations is the best way to insure proper fertilization.  Mulch the plants with straw, leaves, decomposed sawdust, plastic, newspapers or compost to help conserve moisture and reduce the problems of blossom-end rot.  In extreme drought, plastic may increase blossom-end rot if plants are not watered.  Tomatoes require approximately 1.5 inches of water per week during fruiting. This amount of water should be supplied either by rain or irrigation. Extreme fluctuations in soil moisture result in a greater incidence of blossom-end rot.

The plants may be sprayed with a calcium solution. Use products containing calcium nitrate or calcium chloride.  Be sure and follow all label directions.  Most of the calcium sprays should be applied at least once per week, beginning at the time the second fruit clusters bloom. These materials can be mixed with the spray that is used for control of foliar diseases.  Several spray materials containing calcium are available and all work well for tomatoes.

Some varieties of tomato tend to be more sensitive to conditions that cause blossom-end rot than others.  Keep records of tomato planting and the results.  If you can follow the above mentioned steps, you may reduce the occurrence of blossom-end rot and you will be able to enjoy great tasting tomatoes.

Another common question we receive from many gardeners, deals with poor fruit set on tomatoes.  The plants look great and have a good color, but are not setting tomatoes. Several conditions can cause tomatoes to not set fruit.  Too much nitrogen fertilizer, nighttime temperatures over 70 degrees F., low temperatures below 50 degrees F., irregular watering, insects such as thrips or planting the wrong variety may result in poor fruit set.  Any of these conditions can cause poor fruit set, but combinations can cause failures.  If recommended varieties are used, the most common reason tomato plants do not set fruit is because they are not planted where they can receive 8-10 hours of direct sunlight daily.  Any less direct sunlight will result in a spindly growing, nonproductive plant with healthy foliage.

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