If you leave sunflowers in the garden after they have finished blooming for the summer, even one plant will provide plenty of seeds for hungry birds, with enough dropped on the ground to start next year's sunflower crop. However, if you want to plant sunflowers in a different spot, or share the seeds with other sunflower lovers, saving the seeds for planting later is an easy process.
Let the sunflowers remain on the stem until the back of the heads turn yellowish brown and the petals begin to fall off. If the squirrels and birds are eating too many of the seeds, protect the blooms by covering them with large paper sacks.
Cut the sunflower heads off, leaving at least 12 to 15 inches of stem intact. Tie a string around the stem and hang the sunflower heads in a dry, airy spot until they're so dry that the sunflower seeds come loose easily. It usually takes several weeks for the seeds to dry completely.
Rub your hands over the flower head to dislodge the seeds. Put the seeds in a small paper bag or envelope and put them in a dry, cool place until spring. Don't store the seeds in plastic or glass, because moisture can develop which could cause the seeds to develop mold.