you have plenty to harvest now. Get the black seeds, there will be chaf too but that will blow off. I let mine set out on the covered patio to make sure they are dry. Then I dump them all in a can for next year. You might find collecting takes a week or two. I gently grab where the seeds are and gently pull catching the seeds in my hand. Sort of like stripping off the seeds.

Just to make sure I understand you - You are saying to pluck the black seeds off now and leave the rest of the flower head to continue producing harvestable seeds.??

yes. i harvest seed over 2 - 3 week period. you will know because there will be less flowers so less seeds. Then the plant starts to look thin. That's when I pull them out. I use this as ground cover for my veggie raised beds and to keep the bees happy.

Thanks for your help meyerk9. I went out this morning between rain showers and harvested a few seeds. I will wait until they dry in the sun before harvesting any more seeds.