There is no standard definition for the term "heirloom vegetable." However, most experts will agree there are certain characteristics that determine whether a plant should be considered an heirloom. The first of these characteristics is that the plant must be an older variety. The second is that the plant must reproduce true to type, and the third is that the plant must have great flavor.
How old a variety must be to be considered an heirloom is still in debate. Most experts agree that they are plants that have been around since before the rise of the hybrids, between World War II and the 1950s, and the advent of the big commercial farms. But many heirlooms are even older, with some species dating back four hundred years or more.
Some people will exclude certain older varieties of seeds from being heirlooms if they have been commercially sold. However, many of these seeds were of such interest in the earlier part of the twentieth century that seed companies spread them to other areas where they did well, leading to different strains of the same plants that were resistant to local pests and diseases. This made the plants easier to grow, and more likely to be kept.
Heirloom vegetables, unlike their hybrid cousins, generally reproduce true to type through open pollination. If a gardener saves seeds from the best producing plants one year for planting the next, the second crop will be identical to the first. It is this trait that made it possible to save these plants, with seeds passed down for generations from gardener to gardener, and sometimes by seed companies themselves.
It should be noted that even with heirlooms there is no guarantee that a plant will reproduce true to type; undesirable traits can pop up and should be weeded out of the line. It should also be remembered that not all plants reproduce by seeds; potatoes, for example, are not produced from seed, but from the eye buds of the vegetable itself. And it does not mean that care should not be taken when planting different varieties of the same vegetable. These plants will cross-pollinate, creating hybrids that will not have the same traits as the parent, with seeds that will often not be fertile.
Hybrid vegetables have been bred for traits that commercial growers consider more favorable, such as surviving being shipped great distances, ripening at the same time, and growing to the same general size and shape for maximum capacity. The hybrids are usually picked in an unripened state and then ripened in transit through the use of a gas. While these traits allow people to have fresh vegetables year round, flavor is sacrificed in their favor.
If you want to start grow your very own vegetables, heirlooms are the perfect pick. There is no need for the vegetables to survive long distance transportation, and taste takes its proper place as a main reason for growing the plant. Another advantage for home gardeners is that because they ripen naturally, they will not do so at the same time. And because the plants develop naturally, they will have greater nutritional value than the commercially grown hybrids.
With the advantages heirloom vegetables offer the home gardener, it is no wonder more people are turning to them. Seed banks and sharing programs have risen as a means of saving more of these varieties. Through the efforts of these programs, and of gardeners growing them for their historical value, of small farm growers growing them for local markets, or home gardeners for their taste and nutritional value, heirloom vegetables will be available for future generations to experience the way these foods are supposed to taste.