Place 1/2 cup cornmeal or regular table salt into a plastic bag.
Pull two or more flowers out of your faux arrangement, depending on the size of the bag. If you are not confident you will be able to put the blossoms back into the arrangement so they look attractive, it is best to only remove one or two stems at a time.
Place the faux flowers inside the bag, and twist the opening of the bag so that none of the salt or cornmeal falls out.
Shake the bag with the flowers inside for about two minutes. The salt or cornmeal rubs against the petals and other surfaces of the flower. The abrasion removes built-up dust and grime.
Inspect the flowers; if you are satisfied with the appearance, replace them in the arrangement. If not, shake them again.
Run cold water into a sink or plastic basin. Warm or hot water may melt certain parts of the faux flower if they are put together with adhesives. This method is not appropriate for faux flowers with hand-wrapped stems.
Add a squirt of mild dishwashing liquid to the basin. Use your hand to swish the water around to form suds.
Remove one flower at a time from the arrangement. Test one of the flowers in an inconspicuous area. Dip your fingers into the water, rub a petal or leaf for a minute and then blot it with a towel. If the color does not bleed or fade, it is colorfast. Do this before attempting to wash any flowers you are not certain can withstand the treatment.
Place the colorfast flower in the sudsy water, and swish it around to remove the grime. If you see any stains, rub the stain off with your fingers. Don't allow the flowers to soak; if they are attached with an adhesive, the soaking action may dissolve it.
Remove the flower from the water. Shake it gently over the basin to remove excess moisture. Blot the flower well with a soft towel. Replace the flower in the arrangement, and repeat the method with all the other faux flowers.