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Blossom-end rot, seen on this tomato, is a common problem in home gardens. It is typically caused by uneven watering, which prevents enough calcium from reaching the fruit. (Photo by MSU Ag Communications/Scott Corey)

Prevent common problems for ideal garden tomatoes

MSU Extension Service

MISSISSIPPI STATE – While nothing may beat the fresh taste of a home-grown tomato, a lot of things can go wrong in the garden to prevent the fruit from ever making it to the table.

Garden experts say tomato plants should be watered well, fertilized correctly, grown in direct sunlight and spaced properly so their leaves stay as dry as possible.

David Nagel, vegetable and home garden specialist with the Mississippi State University Extension Service, listed three common problems that can plague tomato plants.

“Blossom-end rot, usually caused by uneven watering; early blight, caused by a fungus; and poor fruit set, often caused by over-fertilization and temperatures above 94 degrees, can all affect a tomato plant’s ability to produce good fruit,” Nagel said.

Proper moisture helps to prevent blossom-end rot. Apply one inch of water each week and two inches a week when fruit are set, Nagel said.

Rick Snyder, Extension greenhouse tomato specialist, said blossom-end rot is the result of a lack of calcium in the fruit, even though there may be enough calcium in the soil, leaves and stems.

“Calcium is not transported well in the plant unless conditions are ideal, so sometimes calcium does not make it all the way to the fruit,” Snyder said.

Only a soil test will show if calcium levels are low in the soil. If the soil pH is low, add limestone, which is calcium carbonate, to raise the pH as recommended. This will also add the needed calcium. If the calcium is low but the pH is correct, side dress with calcium nitrate --not ammonium nitrate -- to be sure enough calcium is added to the soil.

Soil tests are available for a small fee through county offices of the MSU Extension Service.

“If you just didn’t get around to doing your soil test as you meant to, go ahead and use calcium nitrate to be sure there is adequate calcium in the soil,” Snyder said.

Mulching tomato plants to hold in moisture can help prevent blossom-end rot. Only root hairs can take up calcium. Snyder said if the plants wilt, root hairs die and the plant cannot take in calcium in adequate amounts.

Early blight, caused by Alternaria fungus, is another problem tomatoes often face in the summer.

“Keep the leaves as dry as possible by spacing the plants so that wind can blow through them, and treat with fungicides if early blight appears in your garden,” Nagel said.

Address poor fruit set by carefully following fertilizer recommendations. In Mississippi, grow tomato varieties that are heat-tolerant.

Some gardeners have been taught to apply Epsom salts, which are magnesium sulfate, to the base of tomato plants. Nagel said these salts are beneficial in very sandy soils that tend to be sulfur deficient or other soils that are magnesium deficient. However, a soil test is the only way to find out exactly what a garden needs.

When a tomato plant is healthy, it can be a generous provider. Nagel said a Sweet One Hundred can easily produce 100 tomatoes, although a Sweet Million won’t make that a million.

“Depending on type and variety, most tomatoes should give five clusters of fruit,” Nagel said. “Indeterminate varieties may make as many as 10 clusters in ideal conditions. Large-fruited ones may have three to a cluster, and grape varieties may have 25 or more in a cluster.”

Most Mississippi gardeners know to have their tomatoes planted by Easter, but not everyone realizes a second crop can be grown, too. Fall tomatoes grow very well in Mississippi. Depending on the planting zone, fall tomatoes should be transplanted sometime in July.

Released: June 21, 2012
Contacts: Dr. Rick Snyder
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