If you have fennel herb growing in your garden for the whispy fronds which go so well with baked fish, eggs and salads, do leave a few heads to go to seed. Once they have dried and ripen in the late Summer sun harvest the heads straight into paper bag or bowl so that they don't disperse far and wide. Rub between your hands to detach the individual seeds and pick out any stalks or dried leaves.
Store out of bright sunlight ready to include in those pickles and dishes where nothing but fennel seeds will do