Remove the zinnia flowers from the plant only when they are completely dead. Select brown flowers that are dry to the touch.
Snip the dead flowers off the stem. Use pruning shears and cut the complete flower head off the plant.
Place the dead flower petals on the plate and set the plate on a flat surface.
Break the zinnia flower heads apart. Use your hands and gently pull the dried petals from the flower's center. Use caution not to tear the petal in half.
Plant the zinnia seeds into the garden or store them for later use. Place the seeds inside a plastic bag. Store the bag inside the refrigerator or a cool, dry and dark place.