To produce plants for seeds resembling the parent plants, pollination must occur only within that particular variety. Since self-pollinated types do not generally cross, isolation is not necessary unless absolute purity of a strain is desired. .
Cross-pollinated varieties have the potential to cross (exchange pollen) with another variety of the same species. If two cross-pollinated varieties of the same species are to be saved for seed, they must be isolated from one another. This is especially true of corn. However, for plants that easily cross-pollinate, it may be more practical to develop seeds in alternative years to keep the strains as pure as possible.
There are some vegetables that will cross-pollinate within their own species; squash, pumpkin and cantaloupe are a few that do, with picturesque results. Vegetables produced by such crosses are edible, but not always of the same quality as the original.
Each season I grow both hybrid and open-pollinated varieties – hybrids for earliness, vigor, disease resistance, and flavor; and open pollinated because some varieties I especially like and, just in case I want to save some seeds, I have them at hand.
Vegetable Classification and Seed Storage Life
Life (in years)