Dahlias — some dahlias — lend themselves well to the flower-drying process. And while dried dahlias aren't the same as fresh, some of the color and most of the form remains.
Folks who have tried drying dahlias agree that some techniques work better than others. They don't lend themselves to pressing; there's too much substance to the centers. And they don't work well for hang-drying; some kind of drying agent, or dessicant, is required.
The best flowers to use for drying, according to dahlia expert Bill McClaren, are the smaller ball and pompon dahlias. These have the most tightly-attached ray florets and the most reliable substance. Tempting as it might be to try to save the gaudy dinner-plate dahlias, they simply have too much water content and they don't lend themselves to working with dessicants.
Some home crafters have had good luck with borax or a blend of cornmeal and borax. Put about a half inch of borax or two-to-one borax and cornmeal mixture into a shoe box; lay two or three flowers on it; completely cover them with the borax or borax mixture and put into a warm, dry place for a week. An advantage of borax is that it's relatively inexpensive and easy to find; it'll be next to the laundry detergents in your local supermarket.
Many seasoned crafters and dahlia-lovers say the best material to use for drying dahlias is silica gel, which can be found at craft and hobby stores. Use silica gel in an airtight container; otherwise it will absorb moisture from the air, not the flowers. Usually 36 to 48 hours is sufficient for small dahlias. Several users report that the flowers look virtually new, and retain their color well. (Not surprisingly, the bronze and orange range of colors dries best.)
Dried flowers have a tendency to reabsorb moisture, so it's not a bad idea to display them from a closed cabinet or under a glass bell. Some crafters spray them with lacquer or other preservative finishes to keep them from drying out.
They're not the real thing, but they'll remind you of summer past and spring to come, when you can plant your dahlia tubers and start the cycle all over again.