The easiest, quickest and most effective way to clean silk flowers is to use a commercial product formulated for silk and artificial floral cleaning. These products are easy to find at craft stores and many discount centers. Spray the product on the dusty silk flowers and you will see the dust disappear.
If your silk flowers only are lightly dusted you can use a can of compressed air that is sold for computer dust removal to blow off dust. A hair dryer or hand-held vacuum also work, but not as well.
Do It Yourself
Commercial silk floral cleaners can be expensive if you have a lot of silk arrangements. There are methods you can use to remove the dust from your silk flowers that work as well as commercial products but will take some time. Before you begin, examine the silk flowers to determine how they are made and what materials were used (see Reference 1). The more delicately the flower is made or if it is hand painted, the more cautious you will need to be. For silk flower arrangements, you will need to carefully remove each flower, clean it, then replace it in the arrangement.
Start by putting the flower in a bag that contains either one cup of table salt or cornstarch. Close the bag and shake it for two or three minutes. Then remove the flower and shake the salt off. The salt or cornstarch will have removed the dust. Another method you can use without removing individual flowers, but should first be tested on a hidden spot of the flower, is to mix a 50/50 solution of cool water and white vinegar. Spray this mixture on the flowers. The vinegar will dissolve the dust.
For very heavy dust you may need to wash each flower. Fill your sink with cool water and a squirt of clear dish detergent. Gently swish the flower in the water until the dust is removed. Remove the flower and carefully dry off the flower as much as you can with paper towels or a dry, soft cloth.