Identify the flowers you would like to decorate the cake with. Use a flower reference guide to determine the breed if you are unfamiliar with flowers.
Determine if the flower is edible. Check a comprehensive list such as the one on NC State or Colorado State University's website. If you don't see your flower in these lists, do not eat it.
Wash all of the flowers carefully under a stream of running water. This will dislodge any dirt, insects or debris that may be caught in the petals.
Use flowers sparingly to decorate the cake. Most people are unaccustomed to eating flowers and may experience indigestion if they consume too much.