When are sunflowers ready to harvest?

[Aida]

Hi everyone!
I have three sunflower heads that have bloomed and lost all their yellow leaves, are now "bending down", and I've rubbed off the little buds in the middle. They're full of hard seeds, but the seeds are snow white, not striped. They've been like that for a LONG time now- should I have already harvested them earlier?

[Dillbert]

there's black, white and striped varieties.

generally you want to leave them on the stalk for as long as you dare -

what's the dare bit? well, birds & critters will clean them out in a day or two - some folk wrap cheese cloth / etc around the heads to keep the critters off.....

[applestar]

Protecting is a good idea. There are also beetles and moths that lay eggs in the seeds and grubs and caterpillars will burrow their way through adjacent seeds. If infestation is not severe, you can jut sort through good ones and bad ones, and freeze the "good ones" for good measure.

The green triangular bracts and the back of the seedhead surrounding the stem need to yellow. You can also try plying one of the seeds from the outermost rings and cracking it open. If its really hard to get off, that's another hint that it's immature.

I wait until the back yellows then cut off and hang in warm dry area by the stems to completely dry out.