You can actually let the seed head fall to the ground and they will self sow. Alternatively remove when ripe, extract the seeds from each berry fill a pot with seed compost, scatter the seed over the surface, cover with grit, label (most important), put into a container of water for half an hour or so (or use moist compost). Then put them outside somewhere in a corner and forget them for months... check and you may well find that they are growing :-)