Never fear. Shopping for seeds is pretty easy once you understand what a few seed-speak terms mean.
Variety: A "variety" is simply a version or strain of a plant. Different varieties have different characteristics, for instance, better disease resistance or a flavor different from other varieties of the same plant. You might be willing to buy a "tomato" in the supermarket, but if you are growing your own, you'd probably rather buy "Brandywine," "Sweet Million," or other varieties with better flavor that may not be able to travel the thousands of miles required of grocery-store tomatoes. You may also see the term "cultivar" (literally cultivated variety), which is used pretty much interchangeably with "variety" in the seed world.
Organic seeds: Seeds marketed as organic were grown on a certified-organic farm and have not been treated with pesticides or coated with chemicals to prevent rotting or premature sprouting. They've also never been genetically modified (GM) with things like bacteria or other plant DNA (more on GM seeds later). Buying organic seeds is worth it because it protects the environment and people on seed farms from harmful pesticides. You're also supporting organic agriculture and breeders who are working to develop new varieties that do well in organic growing conditions.
However, if you can't find organic seeds in the variety you'd like to grow, go ahead and buy conventional seeds. The amount of synthetic chemicals riding along with a seed is very tiny, with one exception: seeds coated with fungicide to keep them from rotting before they sprout. Seed catalogs and seed packets usually note if seeds are treated so you can usually avoid them. Also, the FDA requires seeds treated with poisonous chemicals to be dyed—those I've seen are usually shocking pink— to prevent confusion.
Pelleted seed: Some tiny seeds are available in "pelletted" form. This basically means that the seeds themselves are coated with some inert material (usually clay) that dissolves once you plant the seed. The idea is to make tiny seeds easier to plant and also allows you to distribute them in the soil in a more uniform way.
Hybrid varieties: Regardless of what you may have read or heard, there is nothing inherently bad about hybrid varieties; some are wonderful plants and perfect for organic gardeners because of their disease resistance. A hybrid seed is the product of a farmer carefully making sure one specific plant variety cross-pollinates and fertilizes another specific variety. This is done because both varieties have desirable characteristics and, combined, those characteristics can create a much more desirable offspring variety.
Hybrid seeds are always labeled "hybrid" and/or "F1" (first-generation offspring) or "F2" (second-generation offspring). But what can get confusing for home gardeners is that you can't save seeds from your hybrid varieties, plant them the following season, and expect to get the same results. Every seed produced by a hybrid variety will grow into something different. In order for hybrid varieties to retain the desirable characteristics of both parents, the parents have to be crossed each season.
When shopping, look for hybrid varieties that exhibit characteristics you want, for instance, great taste, tender skin, high nutrition or a hybrid variety that ripens over a long period to spread out your harvest. Hybrid varieties that offer high productivity and good disease resistance, as well as great taste and tenderness, can be wonderful choices for your organic garden. Johnny's Selected Seeds, a major supplier of organic seeds for gardeners and small farmers, sells quite a few organic hybrid varieties.
GM seed: Because most genetically modified (GM) crops are grown commercially (corn, cotton, soy, canola, and sugar beets are the primary GM crops on the market now), it's unlikely home gardeners will every buy them, the two exceptions being summer squash and maybe sweet corn. But it helps to know the difference between hybrid and GM seeds.
Unlike hybrids, which are created when two plants are cross-pollinated to make a third plant, GM varieties are plant varieties that were created by the insertion of genes that may have come from another plant, a bacterium or other microorganism, an animal, or even a lab. The genes can be inserted by creating a tumor in the original plant or by using a "gene gun" that literally shoots new genes into cells of an existing plant in a Petri dish—a process as far from natural as you can possibly imagine.
Though you may never buy a GM plant variety, the chances of getting varieties with GM genes in them by accident, however, can be high, especially for vegetables that are closely related to widely planted GM commodities, such as field corn, soy beans, and beets. Stick with standard or older hybrid varieties of those crops to avoid getting GMO varieties. Unfortunately there isn't much you can do to completely avoid stray GM genes in the other veggies mentioned, especially any type of corn seed (corn pollen can travel for miles on the wind), except not grow them at all—another reason we need to put tighter restrictions on GMO crops.
Open-Pollinated varieties: These are plants that are created in the most basic form—pollinated by either bees or wind. Unlike hybrids, open-pollinated seeds will reproduce true to type, meaning the offspring will display the same characteristics as the parent plant, and seeds can be saved from season to season. However, if you save seeds from an open-pollinated tomato variety and you live in the northeast, your subsequent tomato offspring might taste very different from the same tomato grown by a gardener living down South. Your variety has adapted from elements in your particular climate and environment, and theirs has too.
Heirloom varieties: Just exactly how long a standard variety has to have been around to become an heirloom depends on who you talk too, but the end of WWII is usually the most recent cut-off point. That marked the advent of chemical-dependent agriculture and the selection of varieties that grew well in those conditions. Heirlooms can be great choices because they were developed to grow well in organic conditions. They have also pleased generations of small growers and gardeners well enough to have survived, so they are usually easy to grow and tasty. All heirloom varieties are open-pollinated (though not all open-pollinated varieties are heirlooms), and that means you can save seeds from this season's harvest to plant next year.
So which kind of seeds should you buy? Shop organic when you can. Other than that buy varieties that appeal to you and have characteristics that suit your needs and your growing conditions, whether they are hybrids, standards, or heirlooms. Here are a few places to start looking:
High Mowing Seeds: heirloom & hybrid seeds, all certified organic
Seed Savers Exchange: all heirloom seeds
Seeds of Change: heirloom & hybrid seeds & seedlings, all certified organic
Johnny's Seeds: heirloom & hybrid seeds, some organic varieties