Facts on How Big Tomatoes Grow

Native to South America, the most popular garden vegetable in the United States -- the tomato -- was once considered poisonous. Since popularized by Thomas Jefferson, however, tomatoes (Lycopersicon esculentum) have been widely cultivated as a vegetable crop, with hundreds of varieties grown today by home gardeners. Each cultivar has its own characteristics that determine a tomato fruit's shape, color and size, from tiny currant tomatoes to the world record-holding "Delicious" giant variety.

The growth characteristics that determine how big a tomato fruit becomes are mostly part of a cultivar's genetic makeup; the rest relies on proper planting and ongoing care throughout the growing season. First, tomato varieties are divided into determinate and indeterminate types. The former grow to a specific height, whereas the latter will continue to grow until killed by frost. Thus, it is not uncommon for indeterminate tomato vines to grow as high as 20 feet or more. Generally indeterminate varieties grow the largest tomatoes, although there are exceptions. For example, the "White Currant" heirloom, which produces fruit weighing only .15 ounces, grows on 8-foot-high indeterminate veins. Giant tomato varieties like "Giant Belgium" and "Big Zac" also are indeterminates, but their fruit weighs between 2 and 6 pounds.

However big, or small, the fruit of a tomato cultivar, experienced growers recommend several tips to ensure a plant produces fruit to its maximum size. First, early planting is essential. If using seeds, start them indoors six to eight weeks before your area's last frost date so that young plants can be transplanted outdoors as soon as the soil warms. In addition, select a planting site that provides growing tomatoes a minimum of six hours of direct sunlight every day. Rotate planting sites from year to year to reduce risk of disease. Soil should be loose and well drained. Leave at least 18 to 48 inches of space between tomato plants, depending on the expected final size of the mature variety.

The size and healthy development of tomatoes also depends on soil quality. Adding grass clippings, leaf compost, eggshells, manure and other organic matter helps to enrich the soil and improve drainage. Also, growing plants will need additional boosts of fertilizer as tomatoes grow. Applications of fish emulsion every two weeks helps provide required nutrients to ensure strong plant development. Avoid using excess nitrogen fertilizer, which will produce abundant foliage but few tomatoes. As tomatoes grow bigger, their water requirements remain high. During the heat of summer, irrigate with 2 inches of water per week. In addition, putting down mulch, either straw or plastic, helps retain moisture and can prevent the spread of disease.

Indeterminate tomato varieties, especially those that produce big fruit, require support structures like stakes, trellises or cages to help bear the weight of large vines and giant fruit. Staking also provides the added benefit of keeping fruit and plants off the ground, where they are more susceptible to pests. Tomatoes are not natural vining plants, so stems and large fruit must be carefully fixed to the support using soft twine or pantyhose. Pruning, or pinching off nonflowering offshoots, allows tomatoes to grow to their maximize size, as precious nutrients are more effectively directed to developing fruit.