Easy-to-grow and a cheerful, brightly flowering perennial, blackberry lily (Iris domestica, formerly Belamcanda chinensis) is also called leopard flower because of the dozens of spots seen on the flower petals. Loved by butterflies and bees, the flowers readily form seed capsules teeming with fertile, black seeds. Harvest these seeds when the seed capsules ripen and turn beige, or when they split open. Cut the stems and allow them to dry, releasing the seeds.
Allow the plant to flower and form the swollen seed capsules on the stems across summer.
Cut off the stems with the seed capsules with a pruners or scissors when the seed capsules ripen or break open to reveal the black seeds. The capsules turn beige and become papery before splitting open. The black seeds will persist on the stems for several weeks, giving ample time for you to cut stems.
Place the stems on a sheet of newspaper on an indoor table, allowing the stems to further dry and the seeds to naturally drop off the capsule onto the newspaper.
Gather up the black seeds from the newspaper after 1 to 3 weeks of drying on the newspaper-covered table. Discard the newspaper and plant debris when all seeds are collected. Put the seeds in a paper cup or envelope.
Expose the blackberry lily seeds to a chilly environment, such as in a refrigerator for 7 to 10 days. Sow the seeds outdoors in the early autumn to germinate. Alternatively, sow the seeds in the garden and allow them to naturally sprout in early spring when conditions are favorable.