Edible flowers should be placed on the cake as near to serving as you possibly can so that they don’t wilt and look fresh.
Where To Buy Or Find Edible Flowers - Frolic and Fare
A Florist's Guide to Edible Flowers
Edible Flowers For Cakes Varieties, Types, Taste, Storing & Preserving
How To Prepare Edible Flowers: A Guide » Slow Living Kitchen
The Colorful World of Edible Flowers - Gastro Obscura
How to use edible flowers for cakes and other bakes