Watch your sunflowers as they grow and mature. Wait until the leaves are starting to fall off and the back of the sunflower begins to turn yellow.
Place a paper bag or large piece of cheesecloth or other fine netting over the sunflower. Be sure to cover the entire sunflower head.
Wrap a piece of twine around the paper bag, cheesecloth or netting and wind it several times around the stem. Tie a secure knot and cut off any excess twine with scissors.
Cut the stem below the tie when you are ready to harvest the sunflower seeds. The sunflower seeds are ready to harvest when the back of the flower is brown; you should check periodically under the bag or through the cheesecloth or netting to determine readiness.