By Susan Littlefield

Tomatoes are by far America's most popular vegetable for the home garden, grown by 86 percent of those with food gardens. For all those gardeners out there eagerly looking forward to a harvest of luscious, ripe fruits, here are answers to questions about some common problems that can come between you and the perfect tomato. The problems we've focused on below are all physiological ones -- that is, they are the result of poor environmental or cultural conditions, not insects or disease. Check back next month for information on common tomato insect and disease problems.

Growth cracks (Photo courtesy of David Liebman)

Why do my tomatoes sometimes develop circular or radial cracks?
This cracking occurs when the tomato suddenly enlarges too quickly as it ripens. The cracks usually occur at the stem end of the fruit. Sometimes they form concentric circles; sometimes they radiate out vertically. When tomato fruits are at the mature green stage and the water supply to the plant decreases, the tomato begins to ripen. The thickening of the outer layer of the tomato skin is part of this process. If the plant's water supply increases suddenly again, as when heavy rain follows a period of drought, the fruits enlarge rapidly and this tougher outer layer cracks. Some varieties, especially some of the older ones, are especially susceptible to cracking. To control this problem, try to keep soil moisture consistent by watering regularly, especially as tomato fruits are maturing, and make sure the soil around the plants is well mulched.

Large cracks that radiate out from the stem can also be the result of heat stress, especially when fruits are ripening when temperatures are consistently above 90 degrees F. If you live in an area where summer temperatures are routinely this hot, time your planting so your tomatoes are ripening when conditions are cooler, either in late spring and early summer or in the fall.

My tomato plant has blossoms on it, but they drop off without setting fruit.
This could be because of temperature extremes interfering with proper pollination. If it gets below 55 degrees F at night or above 90 degrees F during the day, your plants may not set fruit until the weather moderates. Don't set your plants out too early in the spring when nights are still cool, and in hot summer areas, time planting to avoid midsummer heat.


What causes puckering and corky brown strips on my tomatoes?
This is a problem called catfacing. It causes deformed, puckered tomatoes with patches and strips of scar tissue, primarily at the blossom end or bottom of the fruit. Catfacing occurs after something interferes with the normal development of the tomato flower such as temperature extremes, especially cold, or drought. It is most common on the first fruits of the season. Don't set out plants too early when the weather is still cool. Older tomato varieties are often more prone to this condition than more modern ones.

The leaves on my tomatoes are curling up. Is this a disease?
Tomato leaf roll is a temporary condition, the causes of which are not completely understood. It usually appears about the time plants are setting fruits and starts on the older leaves first. It often occurs when the soil moisture is excessive, such as after a period of heavy rain. When the soil dries out, the leaves unroll. Leaf roll is most common on plants that are staked or pruned. This condition doesn't seem to have any long-term effect on the growth of the vine or tomato production. Some varieties seem to be more prone to leaf curling than others. If leaf rolling occurs regularly in your garden, it could be an indication that you need to work on improving soil drainage.

Last year my some of the tomatoes on my plants had large whitish blotches that almost looked like blisters. Later these spots started to rot. What's causing this?
Your tomatoes weren't diseased; they were sunburned! Called sunscald, this damage to tomato fruits occurs when they are exposed to a lot of direct sun when the weather is hot. It happens most commonly on staked plants that have been heavily pruned or ones that have lost a lot of leaves to disease. Sunscald usually occurs on the side of the tomato facing the sun. The damaged area first turns whitish and blistered; then later becomes sunken with a papery surface. Eventually rot may start in the damaged areas. Go easy on pruning and try to keep plants healthy to maintain good leaf cover for the developing fruits. Cover plants with shade cloth or row cover fabric during hot, sunny weather if there isn't adequate foliage left on the vines. Tomatoes with rot that's set in are not edible, but if you harvest before rot begins, you can cut away the sunscalded area and eat the rest of the tomato.

Blossom end rot (Photo courtesy of David Liebman)

I look forward to fresh tomatoes from my garden every year, but too often the tomatoes develop a black, leathery, rotted area on the bottom. What causes this and how can I prevent it?
Your tomatoes have blossom end rot. This is a physiological problem, not a fungus disease or insect problem. It is caused by insufficient calcium in the developing tomato fruits. Usually isn't the result of a calcium deficiency in the soil, but occurs because the plant can't take up enough calcium and move it to the fruits because of stress or damage to the root system. One of the most common reasons for this is fluctuation in soil moisture from very wet to very dry. Other causes include excessively wet soil, rapid growth early in the season followed by dry conditions that slow growth down, too much high-nitrogen fertilizer, and cultivating deeply too close to the base of the plant. To minimize problems with blossom end rot keep soil moisture consistent by using mulch, which will also keep weeds down; if soil drainage is poor, plant in raised beds; and go easy on high-nitrogen fertilizer.

Sometimes my tomatoes don't ripen properly. The lower part of the fruit ripens but the top near the stem stays hard and yellow.
This condition is known, appropriately enough, as yellow shoulders. Some varieties, especially some older ones, are prone to this problem; it is usually not a problem on newer hybrids. Hot weather combined with high sunlight hitting fruits as they are developing interferes with ripening. Try to keep plants healthy to provide good foliage cover for fruits or cover plants with shade cloth when the temperature soars.

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