Arctium lappa var. edula is a large and vigorous plant, blooming with large violet thistle flowers in the second year. They cross-fertilize with the wild burdock. Insects take care of the pollination so there should be 500 m between the plot and the wild ones to keep the seeds pure.
Cultivate seeds from selected good, un-branched roots and set with a considerable distance between the roots of about 60 cm.  Either set out directly after harvest or early in spring after winter storage. The ripe brown-black seeds should be threshed out of the prickly burs with a flail or by hand (with gloves). Start by putting the burs in a heavy sack, e.g. a mailbag, which, when trampled and stamped on, makes an easy way of getting the seeds out of the burs. Pick off the large pieces of rubbish and winnow the rest, including the unripe seeds. It is easy to get pure burdock seeds and good seeds should keep for 3-4 years.