Ask the Master Gardener: How to deal with blossom end rot in tomatoes, peppers, squash

Some of my tomatoes are showing signs of blossom end rot. What can I do to stop this?

Blossom end rot is a physiological condition where tissue in the blossom end of the fruit breaks down and starts to rot. This is caused by low calcium levels at the time the fruit is forming. In most cases, the calcium deficiency is not due to lack of calcium in the soil. It is generally caused by inconsistent water, which leads to poor calcium uptake from the soil by the plant. Since we had lots of rain earlier in the season, followed by very little rain, it is not surprising to find this condition showing up this time of year. There are various practices that can help correct and prevent this condition in the future.

Fruits affected by this condition cannot be saved and should be pruned from the plant, since these fruits will still use water and calcium needed for the rest of the tomatoes. Other vegetables such as peppers, eggplants, and squash can also be trouble with this condition. Tomatoes with only slight blossom end rot can be trimmed and are safe to eat, if no other damage is noted.

There are things to be done that will help correct this problem in order to prevent further occurrences. The most important practice will be consistent watering, since too much or too little water will lead to poor calcium uptake. It is best to never allow the soil to become too dry, but keeping the soil evenly moist is the best. Watering deeply, from the bottom, but less often is better than shallow frequent watering. Watering from above can also lead to fungal diseases. Mulching around the plants will also help to maintain even moisture in the soil.

Other measures can be taken to help this problem. Calcium in various forms can be added, IF there is truly a calcium deficiency in the soil. Before adding any calcium boosters, the soil should first be tested for calcium levels and pH. Fertilizing with a fertilizer low in nitrogen but high in superphosphate (such as 4-12-4 or 5-20-5) can help with calcium uptake, along with consistent watering. Calcium can be added by applying lime, bone meal, compost, even crushed eggshells, if the soil test shows a true calcium deficiency. Lime is best added in the fall.

Many people utilize Epsom salts to combat blossom end rot, however there is no research to support this practice. Epsom salts do not contain calcium, but contain magnesium sulfate. I have, in fact, used this product in the past, applying the dry product at the base of the plant and then watering in well, doing this on a regular basis. It did seem to help, however I feel the more frequent and deeper watering probably had more to do with the improvement than using Epsom salts. Certainly, using Epsom salts does no harm, so if you feel this is useful, I see no problem continuing with this practice.

Readers can pose questions or get more information by calling 417-874-2963 and talking to one of the trained volunteers staffing the Mas­ter Gardener Hotline at the University of Missouri Exten­sion Center in Greene County located inside the Botanical Center, 2400 S. Scenic Ave., Springfield, MO 65807.

This article originally appeared on Springfield News-Leader: Ask the Master Gardener: How to deal with blossom end rot in tomatoes, peppers, squash