Take the dusty dried flowers outside or to any area, such as a garage, where you won't mind blowing dust into the air. If there is no electrical outlet for a hair dryer, you will need to use a can of compressed air.
Turn the hair dryer onto its lowest setting and use no heat if that is an option. Hot air can damage and discolor dried flowers if applied for too long.
Work the hair dryer in short sweeping motions all over the dried flowers. With compressed air, don't get too close or you could damage the flowers with the powerful emission. Always keep the air moving and sweeping away from the flowers to keep the dust from blowing around in a circle right back onto them.
Follow hair dryer-dusting with a few sprays of compressed air on stubborn or hard-to-reach areas for extra-thorough cleaning. This final round of non-contact, heavy air dusting should remove even the most caked-on layers of dust without damaging the flowers.