Tomato blossom end rot

Everybody’s favorite garden tenant, the tomato, is on the agenda today. The tomato is arguably the most widely grown of all garden plants, edible or otherwise. It is not, however, immune from its share of cultural challenges. This week we take our annual look at one of the early fruiting problems of tomatoes-blossom end rot.

Blossom-end rot is probably the most common problem tomato growers face. It shows up as a round, sunken, water-soaked spot which develops on the bottom of the fruit. The spot enlarges, turns brown, and feels hard and leathery. The disorder always starts at the blossom end, and may grow large enough to affect up to half the fruit.

Blossom-end rot can also occur on squash, peppers, and watermelons. It is caused by a lack of calcium in the developing fruit resulting from one or more of the following: (1) extreme fluctuations in soil moisture, from very wet to very dry, (2) rapid plant growth early in the season, followed by very dry soil, (3) excessive rain or irrigation that smother root hairs, (4) high levels of soluble salts in the soil from overfertilization, (5) cultivating too close to the plant, and (6) a deficiency of calcium in the soil. The severity of this problem can be compounded when two or more of these factors interact with each other, and can occur even when there is abundant calcium in the soil and tissue tests show high levels of calcium in the plant.

The first fruit are the most severely affected by blossom-end rot. Mold may grow on the rotted surface, and result from fungi or bacteria that invade the damaged tissue. The rotted area is of no value but the rest of the fruit may be edible.

What to do? Blossom-end rot can be prevented or at least managed. To help prevent blossom-end rot, follow these guidelines: (1) Maintain uniform soil moisture by mulching and watering wisely. Apply enough water at each irrigation to wet the soil to a depth of 18 to 20 inches. Water when the soil two inches deep is barely moist; (2) avoid using high nitrogen fertilizers. For example, applying 5-10-15 instead of 10-10-10 would be advisable. Also avoid the use of fresh manure in large amounts. Use nitrogen in the form of potassium or calcium nitrate and avoid ammonium nitrate if possible, since ammonia tends to chemically inhibit the uptake of calcium. Applying several small side dressings is also better than applying a large amount of fertilizer at one time; (3) plant in well-drained soils. A larger, healthier root system is more able to take up calcium and other nutrients; (4) avoid cultivating deeper than one inch within one foot of the plant so as to avoid destroying valuable feeder roots.

Next: More tomato problems and solutions.

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478)954-1507, timlewis1@windstream.net and at LewisFarmsNursery.com.