I leave them on the stalk until they are brown. But first, I wrap the flower head with maybe cheesecloth or a piece of tule ???- (whatchamacall that netting like matterial that brides like to use for veil?) & tie the cloth with a strip of nylon or t-shirt - whatever. The cloth will keep Goldfinches from eating the seeds. :-) Don't use plastic; the flower head will rot since there is no air circulation around it. Good luck.

I am glad to find this post; I recently asked the same question (I THOUGHT I looked for the topic carefully!), and have had no one respond. Now I feel a little silly finding that the answer was here all along, but am mainly just relieved that I know what to do with this plant; it's the most beautiful and magnificent sunflower I've ever grown (actually I can't take any credit whatsoever, because it's a volunteer, at a house we just bought last year! At least I knew enough to identify the plant when it came up, and didn't "weed" it!) The trick for me is that I couldn't get up to look at the flower 12' up to try to assess the seeds' readiness; I've been in a wheelchair (now graduated to crutches) this summer. Now I know that I've just got to get some netting, and send DH up a ladder with the mission. Hopefully, he'll be willing! Thanks pitimpinai (and shlisten for asking "my" question!)

Mountainsong

can i belabor this discussion with one follow-up question? WHEN should we wrap the flowerhead with protective cloth? Before it turns brown, while it is still flowering, or soon after the petals have faded/fallen?

I too have an amazing volunteer this year, with luscious blossoms in abundance and I want to save a good number of seeds--more details re. timing are appreciated.