Evergreen Bunching Onions (Allium fistulosum)

Onion seeds are not typically difficult to grow or to collect, but keep in mind that they are a biennial crop, meaning that they seed once every two years. Watch first for flowers and then for seed heads to form during the late summer of the second season. Wait for the seed heads to dry. Most of the flowers will be dry, and the seeds will begin to fall out on their own.gather the heads in a paper bag. Most of the seeds will fall out on their own; shake the bag to free the remainder of the seeds. Separate the seeds from the stems and other matter that makes up the seed head. Allow the seeds to air-dry for a few days before storing the seeds in a cool, dry place. Seeds remain viable for 2 years.
-Information from Seed Savers