Once the first flowers appear, support them with canes, one for each plant. Alternatively support the plants with stakes at each end of the bed and at intervals in the row. Then tie several rows of string along the outside of the crop to keep stems in and supported.
The leek flowers later than onions producing usually just one seed head per plant.
After the plants bloom and seed heads begin to dry, gather the heads in a paper bag and shake the seeds free. Allow the seeds to air-dry for a few days before storing the seeds in a cool, dry place.