As summer fades, wildflower seedheads dry out and turn brown. Collecting your own seed is not only satisfying, but it also provides you with hundreds of free plants for next season.
Choose a dry, sunny afternoon to collect seeds. Snip the dry seedheads and place them into paper bags (never plastic, as plastic traps moisture and causes mold). Label the bags immediately. Shake the bags to release the seeds, and pass them through a fine sieve to separate the seeds from the chaff. Store the clean seeds in paper envelopes in a cool, dry place. For seeds that require cold stratification (like Primrose), you can sow them directly in trays in autumn and leave them outdoors for the winter.