What frosting should you use on a warm day? Ganache is the safest frosting and has the highest melt point. After that, you have American buttercream but you have to use 50% shortening in hot weather. Wedding cake can be around for up to 8 hours. I will break the rules for a cake that will stay in my refrigerator right up until delivery, and then I know it will be sliced within a short time ie. birthday party but never for a wedding.