Ask Mr. Smarty Plants

Yes, you can store your leftover Rudbeckia hirta (black-eyed Susan) seed until next year (spring or fall) as long as you take a couple of simple precautions to ensure the seed stays viable.  The best way to keep the seed from drying out and loosing viability is to put it into a glass jar, seal it tight and store it in the refrigerator. I have numerous packets of seed in the vegetable crisper of my refrigerator for safe keeping until I can sow them. 

Here's some information from our website about growing Rudbeckia hirta from seed that might be of interest...Propagates very easily from seed sown in fall or spring. Spring-sown seed should be stratified. Rake seed into a loose topsoil or cover with ¼ to ½ inch of soil or mulch. If possible, supplement with water if fall or spring rains are infrequent and light. The seed requires several days of moisture and should germinate in one to two weeks.

Seed Collection: The nutlets turn charcoal-gray at maturity, usually 3-4 weeks after the bloom period. Seeds are mature at this time, but they are easier to collect after cones lose their tight compact structure. Store dry in sealed, refrigerated containers.
Seed Treatment: Stratify for 3 months at 40 degrees.
Maintenance: Black-eyed Susans are drought tolerant but respond well to an occasional watering. Additional irrigation in a dry year will improve the density of the stand and lengthen the flowering season. Do not mow until after the plants have formed mature seed cones, about three to four weeks after flowering. (Check by breaking a cone open and if the seeds are dark, they are mature.) The number of volunteer plants can be limited by removing the seed heads after the flowers are done.