image by Sunflower seeds almost ready to dry
Drying spent sunflower heads with the mature seeds still intact will serve two purposes. It will cause the seeds to harden further, making them easy to remove from the blooms. Sunflowers don't give their seeds up readily unless they're dried first. Drying the seeds will also prepare them for their real purpose in life, other than making more sunflowers. That purpose is to render tasty snacks for you and your family and friends. If the weather's nice and sunny, you can dry them on the stems. If not, this can be done just as easily indoors.
Watch your mature sunflowers for signs that it's time to harvest the seeds. The flowers will look to be dead or dying. They will be wilted, dry and brown, and most if not all of the yellow petals will have fallen off. The undersides of the heads will turn yellow when the seeds are ripe for drying.
Envelop the head of your sunflower in a brown paper bag. Secure it into place by tying a piece of string tightly around the bag and stem near the bag's opening. This will prevent loss of any dropping seeds. Using a paper bag will also prevent mold growth on the flower head by allowing it to breathe and preventing the accumulation of moisture.
Cut the bagged flower head from the plant about a foot below the bag and bring it indoors if you're expecting rain within the next several days. Turn it upside down and hang it in a warm, dry spot with good ventilation.
Open the bag each day to monitor the progress of your project, taking care to collect any seeds which may have already fallen off. Check to see if the back side of the flower head has turned dark brown and very dry, which can take from 1-4 days. That's when the seeds will be dried and ready to harvest.
Cut the flower head from the stalk about 1 foot below the bag. Don't remove it or you risk dropping the seeds on the ground.
Rub your hand across the seeds and they'll pop right off of the sunflower. Collect them in a large colander and rinse well with cold running water. Drain them thoroughly and spread them out in a single layer on a thick towel. Allow the sunflower seeds to air dry for a couple of hours.
Pick out any foreign matter or debris that you can see. Your dried sunflower seeds are ready to eat just as they are, or you can salt and toast them if you wish. Store in air-tight containers or resealable plastic food bags.