Molded rose petals

So I tried to save some rose petal from a bouquet in a ziplock bag. They were all dried out when I put them there but they gradually got soft again and now they’re molded. I’m wondering two things, 1.) How should I properly store them to kept them dry next time? 2.) Is there any spell I could use the molded rose petals in? (Carefully ofc not to get sick)