Most gardeners can relate to the giddy anticipation generated this time of the year when nursery catalogs start filling the mailbox. Aside from all the wonderful nursery stock that inspires oohs and aahs, I spend an equal amount of time studying seed catalogs. I plant seeds for a number of reasons. The most obvious reason is some plants, like pole beans, grow very reliably from seeds and it is not necessary to buy transplants or containerized plants. Another reason is not all species and cultivars are readily available as plants for purchase and seed is the only available means of propagation. And my final reason is the economics of scale. Let's say I want to develop a pollinator garden and my plan calls for ten butterfly weed (Asclepias tuberosa). I can buy a packet of 100 seed for $2.50 or I can buy ten plants that usually cost at least $5.00 each.
That sounds all pretty simple but there are a few other considerations for deciding which seed to purchase. Among the more important considerations is whether you want to save seed from the resulting plants for a later planting. For seed saving purposes, gardeners can save true-to-type seed from open-pollinated and heirloom types, but not hybrids. I make the distinction between open-pollinated and heirloom types because all heirlooms are open pollinated, but not all open-pollinated plants are heirlooms.
So what is the difference between open-pollinated, heirlooms and hybrids? Open-pollinated refers to unrestricted pollination that occurs by wind, insects, birds, mammals (including humans) or some other natural mechanisms. As long as pollen is not shared between different cultivars (cross-pollination) within the same species, then the resulting seed will remain true-to-type. For example, an heirloom that I grow is red-seeded asparagus bean. Because I don't grow any other type of bean in the garden, I can assume the seeds I collect will be true-to-type. If I had grown a different cultivar of yard long bean, I would not be able to make that assumption. Even though the seed would still be viable and could be replanted the next year, that seed would no longer be true-to-type because I had not taken any effort to block cross-pollination (separated by distance or planting date).
The term heirloom comes in when referring to a species or cultivar that has a history of being passed down from generation to generation, and, as mentioned previously, it must be open pollinated.
Hybrids "can" occur naturally, but most commercially available hybrid seed, often labeled as F1 hybrid (or filial 1 hybrid), are deliberately created by man using controlled pollination between two selected parents. Although resulting seed from an F1 hybrid plant can be collected, it will not be true-to-type because the same parents did not contribute to the seed. The resulting seed may also lack the phenomenon of "hybrid vigor" often associated with F1 hybrids. Gardeners using hybrid seed will need to purchase new seed each year.