I am making my brother's wedding cake in June for an outdoor wedding. The recipe calls for 50/50 fondant gumpaste for daisies that stand up on the cake. Will the heat of the outdoors affect the daisies? Should I make the daisies out of straight gum paste? Any help would be greatly appreciated.

I think they will hold up fine.

Will the cake be sitting in the blazing sun, or will there be shelter of some kind? Will it be iced in fondant or butter-cream?

I use decorations made from fondant with Tylose added, and have never had a problem with them melting/wilting, etc. I'm in Georgia where we have heat and humidity! I'd use "gum glue" to attach your daisies (don't know if you do that usually) and give them 4-6 hours to set.

Good luck, and BTW welcome to CC!

The cake is frosted with buttercream which also worries me. I think I'll talk to them about putting the cake under a tent instead of the hot sun. I tried to bring all of the many things that can happen, melted frosting, bugs, etc but they don't seem that worried about it. Thanks for your help and the welcome!!

Well good luck in persuading them to move the cake to somewhere more stable...it's not like we really know what we're talking about...

Oh, and since it will be BC, just disregard the part about attaching the flowers with gum glue.