Pollinating

A bit more on saving seed from You Grow Girl site.

Self-pollination and Cross-pollination

Plants either have all the parts to pollinate themselves, (called self-pollinators) or they are aided in accomplishing this by insects, the wind, or human intervention (cross-pollinators). Self-pollinators are commonly referred to as 'perfect flowers' as they contain all the parts to successfully pollinate themselves. The comparatively imperfect cross-pollinators produce all the parts to pollinate, but not all in one place. Parts are divided between blooms or are 'self-incompatible', identifying their own pollen as foreign material. Pollen must find its way from one plant to the next. This method is preferable for the survival of the species because it ensures that the plants produce genetically diverse seeds - seeds that contain different genetic information or traits then the original plant. This enables the plant to better adapt itself to the environment it is in, or acquire traits that will help it become more disease resistant. Self-pollinators on the other hand, essentially produce clones, which makes them more susceptible to any problems that may arise.

Be aware that if you want cross-pollination to occur in your garden, you need to make your garden favorable to pollinating insects or be prepared to do all the pollinating yourself. Grow plants nearby that attract pollinators - butterfly bush, Queen Anne's lace, bee balm, salvia, and cleome are a few, and avoid using chemical sprays that will kill all insects both harmful and beneficial. In some cases you might want to keep cross-pollination from taking place. Plants that are closely related, for example different varieties of melons, will cross-pollinate producing seeds that are a mix of the two varieties. If you want to keep your varieties true, plant similar species of plants on opposite ends of your garden.