Why use Silk flowers vs. real flowers?  Not only are silk flowers just as beautiful, they are light weight, less expensive and will stand the test of time. I love working with silk flowers.  They allow me to be creative and versatile during the entire year, when some real flowers are not available. They're an ideal and lasting gift for someone special or for those suffering allergies and who cannot have fresh arrangements around them. They are durable, look good day after day, and don’t need any watering or special treatment to keep them looking fantastic. Some flowers are sensitive to gases emitted by foods so they are not usable on buffet table of fruits or vegetables, such as carnations.  Fragrances on real flowers tend to conflict with other aromas such as food or perfumes used at weddings. 
When using real flowers on your wedding cake, make sure to use only nonpoisonous flowers.  This would not be a problem with silk floral designs.