Extension

For many vegetable gardeners, nothing says summer quite like a vine-ripened tomato. Gardeners spend weeks planting, watering, fertilizing and nurturing their plants while eagerly anticipating that first ripe, red tomato.

Unfortunately, tomato plants can present a few challenges along the way. Whether blossoms are dropping before fruit develops, tomatoes are developing dark, sunken spots on the bottom of the fruit or physiological leaf roll, many common tomato problems are related to environmental conditions and plant stress.

One concern gardeners often encounter early in the season is poor fruit set or blossom drop. Tomatoes are sensitive to temperature fluctuations, and flowers may fail to develop into fruit when nighttime temperatures fall below about 60 degrees Fahrenheit or rise above 70 degrees Fahrenheit. Fruit set also declines when daytime temperatures consistently exceed 92 degrees Fahrenheit. Under these conditions, blossoms may simply drop from the plant or produce misshapen fruit.

Excessive nitrogen fertilization can also contribute to poor fruit production. While nitrogen encourages lush, green growth, too much can result in vigorous foliage development at the expense of blossoms and fruit. In addition, dry soils, root damage and excessive shade can reduce flowering and fruit set. Tomato plants need at least six hours of direct sunlight daily for optimal production.

Gardeners can help improve fruit set by planting early-, mid- and late-season varieties at the appropriate times, growing tomatoes in well-drained soil rich in organic matter and providing consistent moisture throughout the growing season. Mulching with straw, black plastic or other materials helps conserve soil moisture and moderate soil temperatures. Hormone-type blossom-set sprays are available and may help reduce spring blossom drop caused by cool nighttime temperatures, although they offer little benefit during periods of excessive heat.

Even when fruit develops successfully, another common problem can appear just as tomatoes begin to size up. Gardeners may notice a small, water-soaked spot near the blossom end of the fruit. The spot enlarges, darkens and becomes sunken and leathery. This condition is known as blossom-end rot, or BER.

Blossom-end rot is a physiological disorder caused by a calcium deficiency within the developing fruit. The problem most commonly affects fruit when it is about one-third to one-half grown. Although calcium may be present in the soil, environmental conditions can prevent the plant from supplying enough to the developing fruit.

BER often occurs when plants experience rapid early-season growth followed by prolonged dry weather. Factors that increase the likelihood of blossom-end rot include inconsistent watering, heavy nitrogen fertilizer applications and hot, dry winds.

The best defense against blossom-end rot is preventing plant stress. Provide an even water supply throughout the growing season and avoid allowing plants to become excessively dry. Mulch can help maintain consistent soil moisture and reduce temperature fluctuations around the roots. Tomatoes should be planted in well-drained soil and irrigated during hot, dry periods. When possible, select planting locations that offer some protection from strong winds.

Gardeners may notice older leaflets on tomato plants curling upward. This is physiological leaf roll. Rolled leaves are firm and leathery. Aside from leaf rolling, the plants appear normal in size and appearance. Affected plants will continue to grow normally with little or no reduction in yield or quality.

Physiological leaf roll has been associated with tomato varieties carrying a specific gene that favors this condition, the occurrence of high temperatures and prolonged periods of wet soil. Leaf roll is often more severe on staked and pruned plants. Aside from planting tomatoes on well-drained soils, there is little that can be done to correct leaf roll.

Whether dealing with blossom drop, blossom-end rot or physiological leaf roll, the key to healthy tomato production is consistency. Providing adequate sunlight, proper fertility and regular moisture helps reduce plant stress and encourages strong flowering, fruit development and high-quality harvests. With a little attention and care, gardeners can look forward to enjoying plenty of delicious homegrown tomatoes throughout the summer season.