The seeds of heirloom tomatoes, also called open-pollinated tomatoes, keep their characteristics generation after generation. The offspring of hybrid tomatoes behave unpredictably, taking after one parent or the other, or a combination of both. While most horticulturalists believe that hybrids resist disease better and are well suited as commercial field tomatoes, they also agree that home gardeners will enjoy better real, summertime tomato flavor from heirlooms.
Most heirlooms available today date from the period between the Civil War and the 1960s, when agricultural research into hybrid tomatoes suited to mechanical harvesting took off and interest in heirlooms languished. The sustainable agriculture movement of the 1990s refocused public attention on the value of heirloom vegetables.
Many heirloom tomatoes of high quality came to be developed in Eastern Europe, as well as France, Italy and by immigrants and Native Americans in the United States. Examples include Cherokee Purple, with its links to Native Americans; Brandywine, with roots in the Amish farmland of Pennsylvania; and Black Krim, developed on the Black Sea; and Stupice and Slava, from the Czech Republic.
While many heirloom fruits ripen to red, yellow and orange, other unusual colors and even striped and multicolor versions exist. Purple tomatoes, native to the Southern Ukraine according to California tomato grower Gary Ibsen, also hail from Germany, Yugoslavia and the United States. Green varieties include Aunt Ruby's German Green, Green Grape and Green Giant, and generally are ripe when soft to the touch. White heirlooms include Potato Leaf White, White Queen and Halfmoon China.
Most heirloom tomatoes do not resemble store-bought tomatoes. They may be lumpier, less symmetrical and thinner skinned, as well as appearing in colors other than red. Some also sport potato leaves, simple lobes without the serrations of regular tomatoes.
Seed Savers Exchange in Iowa offers its members heirloom seeds. You can also obtain them from online seed retailers, heirloom specialist web outlets, organic grocers and even garden centers. Additional sources include the Landis Valley Museum in Pennsylvania, the Tomato Growers Supply Co. in Florida and the Southern Exposure Seed Exchange in Virginia (see Resources).
Heirloom tomatoes "definitely" surpass hybrids in their taste, according to the Virginia Cooperative Extension. They also contain genetic diversity, with the potential for varied flavor, color and disease resistance, unlike hybrids, which by definition have genetic uniformity.