I am just growing them for the birds and squirrels, but not sure when to harvest them.
They are HUGE!!!
You'll see the center developing seeds as the flower head dries....mostly...you'll notice squirrels have dragged it away at it's peak :-) Otherwise, my usual suggestion is to check on google, ask or bing.
When the birds start landing on the flowers and start pecking the seeds out of the seed heads.
When ripe, the seeds are baklck with white stripes and have a hard shell.
I would just leave them where they are, the brids will find them and then you can cut the rest of the heads off and store in a dry place fpr use in winter.
Today I had to go to a small town 25 mi away and we came by a huge fild of sunflowers. They were only about 16" tall and still blooming. WE had a rainy, cool summer in some parts of ND and the price of unflowers seeds for birds will mostlikely go up.
Well, the birds usually strip mine before I get a chance to do much. I did find a small one the other day and put the head up in a feeder so they could eat it. :)
To prevent bird from stripping them do this: when the seed are ALMOST ripe, get some pieces of old tight woevn sheer curtains to tie over the flower heads.
The seeds will ripen without the birds stealing them ahead of time.
I used to grow them years ago, and what I did was cut off the head with about a foot of the stem when they were just about to ripen (you can tell by the seeds nearest the center). Then I'd hang them upside down in our shed, and they'd ripen the rest of the way. The seeds are very easy to remove when they're fully ripened, and I got many buckets of seed out of them. I did hang a couple outside for the birds to peck at as they ripened, too.
Edited to add: I should mention that the sunflowers I grew were the really large ones. The heads were about a foot across.
Around here you can tell when they're ripe because the squirrels will have carried them off! Tried sunflowers when DS was little - saw a squirrel bolting across the backyard with the entire head of the sunflower in his mouth (they were the smaller sunflowers).
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