Oenothera biennis
Common Evening Primrose
 
Known as Common Evening Primrose, this biennial plant typically grows to 2-3 feet in height and has a spire of butter-yellow flowers. A favorite of bees, the plant is also a host plant to the beautiful, pink, Primrose moth. 
 
Oenothera biennis grows well in moist or sandy, dry soils, and can tolerate both sunny and part shade conditions, making it a valuable addition to just about any garden. Its ecological value comes with its bloom time, as it is often one of the last blooms available late into the Fall. Along with bees and moths, it is also a favorite nectar source for hummingbirds, and the seeds are eaten by the adorable goldfinch.
 
Humans have long used the primrose for herbal medicine and food, as the young roots are edible, and the seeds produce an oil used to treat various ailments.
 
As to seed saving, wait for the seed pods to form after flowering. A mesh bag can be helpful to capture some of the seeds while leaving others for the birds. The seed pod will turn brown, and you want to collect as it is a light brown, with the seeds inside dried to a brown color. Split the pods to retrieve the seeds, and store over winter in a cool, dry location. Direct sow in the spring, or start indoors approximately 6 weeks before the last frost date of your area.