When you think about preserving flowers, the result is always a dried flower that someone has treated with various means to retain its color and sometimes shape. Even though you can freeze a flower, you would never use this method since the flower would immediately decompose after thawing. The most common methods of drying flowers are air-drying, pressing, desiccants and microwaving.
You can dry flowers simply in room-temperature air by removing their leaves and hanging them upside down by their stems in a dark place. You can use a rubber band to hang several together as long as their pedals are not constricted. Hang them from a hanger using paper clips to hook them in place. Although some air movement is good to keep the mildew from growing in the flowers, too much will blow the pedals off the stem. Expect to leave the flowers to dry for four to six weeks.
Pick any leaves or wilted petals from your flower and lay flat between two sheets of absorbent paper. Lay the flower as flat as possible so that it has some form when you have finished pressing it. Extra-woody stems or extra-fleshy stems don't do very well with this method, so you can cut the flower from the stem if you just want to reserve the flower. Add a flat weight on top of the papers to give even pressure. Make sure you have enough absorbent material around the flower to absorb the moisture, or it will just mold. You can use paper bags, phone books, bibles or newspapers for this method. Expect to leave the flowers for four weeks.
Drying flowers with desiccants is one of the faster methods of drying flowers. Submerge the flowers in the desiccant material, which can be silica gel, sand/cornmeal/borax mix or even kitty litter. Place a 1-inch layer of the material in the bottom of your container, place the flower in it standing upright, and slowly add the desiccant around it. Arrange the petals so they do not bend and carefully cover them. Close the container and leave to dry. This method can be finished in as few as three days for delicate flowers or a week for tougher specimens.
Microwaving will give you almost instant dried flowers. It is actually a combination of the desiccant process and the microwave. Bury the flower in the desiccant and in a microwave-safe container. Set a cup of water in with it and turn on the microwave for a minute for small flowers and up to three minutes for larger ones. Keep the flowers in the desiccant for about 24 hours, remove them, and spray lightly with hairspray to keep them from absorbing humidity from the room.