Cosmos are tall bright annual flowers that bloom continuously from late spring to early fall. Collecting the seeds from the flower heads after they have bloomed will allow you to dry and preserve the seeds, then plant them next year in your flower garden.
Check the cosmo flower head to make sure it has finished blooming. The cosmo flower head will finish blooming after the first frost. The appropriate time to remove the heads and the seeds is when there are no petals surrounding the stem. The seeds will be formed in the middle of the flower head in small pockets and they should look dark brown to black.
Pick the cosmo flower head off of the stem.
Choose a flat surface to remove the seeds from the flower head, such as a table. Cover the table with newspaper.
Open up the pockets in the flower heads to reveal embedded seeds. Pull the seeds out of the flower head. Use your fingers to make sure all of the seeds have dropped out from inside the little pockets.
Empty the seeds into the shoe box and allow them to air dry for 6 weeks. Keep the seeds away from sunlight and lightly shake the seeds weekly to avoid moisture accumulation. Make sure that while drying, the seeds remain separated and that they have a chance to dry on both sides. The seeds will turn darker as they dry.
Proceed to transfer the dried seeds into the plastic bag. You can store the seeds in the bag for up to 6 months.
Plant the seeds in your flowerbed the following spring and await the arrival of the brilliant blossoms once again.