Problems With Blossom Rot When Growing Tomatoes

Causes

• Blossom-end rot only affects the fruit. Since it's a physiological disorder and not a disease, it's possible to save the plant so it can later produce healthy tomatoes. Although a calcium deficiency causes the black rotten spots to form, improper soil moisture is usually the real culprit. Combine uneven watering or drought with nutrient deficiencies in the soil, and even the healthiest-looking plant can suffer from blossom-end rot. Overly wet soil can also lead to rot problems.

Soil Management

• A soil pH between 6.0 and 6.5 results in healthiest tomato growth, so it's vital to test the soil before you plant. Acidic soils, with a pH below 6.0, can result in rot if the tomatoes are overwatered. Testing the soil to determine pH two months before you plant and adjusting the acidity with an application of agricultural limestone in the amount recommended by the test prevents this issue. Proper soil fertility at planting also minimizes blossom-end rot. Fertilizer needs vary depending on your soil. It's best to test the soil and follow testing recommendations instead of using a general application rate if blossom-end rot is an issue in your garden.

Moisture Requirements

• Uneven soil moisture, especially periods of dry soil followed by extreme soaking, make tomatoes more prone to rot. Applying a 2-inch layer of straw mulch over the soil after planting helps retain soil moisture so it's less likely to dry out completely. Deep weekly watering, as opposed to frequent light watering, soaks the soil to at least a 6-inch depth so the tomato roots penetrate deeply and have more access to calcium. During hot, dry weather, tomatoes may need more frequent deep watering -- sometimes as often as three times a week. Postpone midseason fertilizer applications until the dry period passes, since too much nitrogen and drought stress can increase the incidences of blossom-end rot.

Treatment

• Usually, rot only affects the fruit forming during the stress period; if you pick and dispose of all black-bottomed fruits, the next flush of fruits won't exhibit any symptoms. Leaving rotting fruit on the tomato plant can also leave it open to bacterial infections, so it's important to promptly remove any tomatoes suffering blossom-end rot. A calcium nitrate or calcium chloride spray can remedy calcium deficiencies if rot problems persist. Dissolve 4 tablespoons of the calcium in a gallon of water and spray it onto the foliage of the tomato plants when temperatures are below 85 degrees Fahrenheit. Apply the calcium three times weekly as the second set of fruits form so they aren't affected by the same rot that plagued the first fruiting cycle.