Sunflowers grow in many sizes and preserving them can be accomplished in several ways. You can dry them to use in floral arrangements or other craftlike projects. You can enjoy them as cut flowers and by incorporating some simple techniques, they can be preserved to last longer than they would otherwise. Or, you can preserve their seeds to enjoy in salads, in culinary dishes or roasted, or simply saved to feed the birds. Your purpose for the sunflowers determines how you preserve them.
Harvest the flowers when they open and are still beautiful. Leave about 2 feet of stem attached.
Place the sunflower in a container with the stem hanging up over the edge. Cover the entire bloom with water-absorbing silica gel crystals sold for this purpose.
Seal the flower and stem in cling film and let it dry for about 10 days.
Mix a floral preservative into a vase of warm water or make your own, such as with one part lemon-lime soda and three parts water.
Recut the sunflower stems at an angle at the desired height and strip off the leaves so none is placed in the water. Arrange the sunflowers in the water.
Change the water when it becomes cloudy and place the sunflowers in a cool location when they are not on display.
Allow the flowers dry out on the plant until the back turns yellow and the seeds begin to darken.
Clip off the heads plus a foot or so of stems and hang them upside down in a warm and dry location. Place a bag or bucket underneath to catch any seeds that may fall. In a few weeks, remove the seeds, which should be easy at this point.
Lay the seeds out to dry for a day or two and place them in a sealable container and store in a dark, cool location.