Onions and leeks do not cross with each other but only grow one variety of each for seed each year. You can grow others for eating, but be careful to spot and remove any flower–heads on them before they burst. They flower in their second season. Leeks can be left in the ground over-winter to flower the following spring and onions which have been stored need to be replanted in spring.

Watch the flower heads carefully as the seeds develop as the pods shatter and scatter the seeds very easily. Cut the heads as soon as you can see black seed inside them and collect them in a paper bag to finish drying. After several days, rub the heads between your hands to Extract the seed; sieve out the debris and store in an airtight jar in a cool dark place. It will last for two years. If the weather goes really wet and nasty before the seed has matured bring the whole plants into the greenhouse or polytunnel for a while before trying to dry them.