How experts define heirlooms can vary, but they are generally at least 40-50 years old. Most heirlooms come from seed that has been handed down for generations in a particular region or area, hand-selected by gardeners for a special trait. Others may have been developed by a university a long time ago in the early days of commercial breeding. All heirloom vegetables are open-pollinated, which means they are pollinated by insects or wind without human intervention. In addition, they tend to remain stable in their characteristics from one year to the next. Many gardeners agree that most heirloom varieties boast greater flavor than that found in hybrids, especially among tomatoes.