Tomatoes are the most widely planted garden vegetable in America, from lavish spreads of backyard vines to single pots containing one plant. With the plants being so common, and with so many inexperienced gardeners trying their novice hands, it is no wonder that tomato-related questions are the bread and butter of many extension services. You might be surprised to discover what causes tomatoes to split, to have lines or to be misshapen.
As a member of the widely cultivated nightshade family, tomatoes are prone to a wide variety of pests and problems. They can be adversely affected by a range of fungi, molds and insects, most of which can spread from related plants such as bell peppers and tobacco. Tomatoes are also susceptible to weather conditions, failing to flourish if the weather is too hot, too cold, too wet or too dry. Even when everything else goes well, voracious birds can damage ripe tomatoes.
Slits, Splits and Cracks
One common flaw you can find in many garden tomatoes is the development of various slits, splits or cracks. One variation of this blemish causes tomatoes to grow in lumpy, irregular shapes with deep creases in them. This is referred to as "cat-facing." A second, unrelated problem causes the tomatoes to grow deep cracks in their skin. These can take two different forms, one being semicircular cracks forming in a ring around the tomato's upper edges, the other being in the form of splits starting at the stem and radiating outward.
Cat-facing is immediately recognizable. It is caused by unseasonably cold weather while the tomatoes are blossoming and pollinating. As the tomato matures, some portions of the fruit will grow lavishly and other portions poorly if at all. The result is a misshapen tomato, with overgrown bulbous regions divided by deep creases. Some cultivars are more susceptible to this than others, most especially the large beefsteak types. If cat-facing is a problem in your area, browse the seed catalogs for resistant varieties.
Cracking and Splitting
Both the circular cracking pattern and the pattern of radiating splitting have the same cause, which is inconsistent water supply. When tomatoes are maturing they are especially susceptible to this problem. It occurs when the soil is allowed to dry out and then rain or a heavy watering suddenly provides an excess of water. The tomatoes take up too much water for their skins to contain, and cracking is the result. You can avoid the problem by watering the tomatoes during dry weather. There are also crack-resistant varieties, which have thicker skins.