This is quite a common concern here in Brisbane. I would recommend firstly choosing a quality florist so you receive the best quality and freshest flowers. Secondly most flowers that are available in summer are pretty resilient to the heat so as long as you keep water up to them they should be fine!
Get your flowers delivered closest to you being ready as possible.
Any buttonholes or corsages place in Fridge until needed.
Pack a little spray bottle in your emergency kit and get a bridesmaid to give the flowers a spritz after the ceremony.
Have some vases of water ready at the reception to pop the bouquets into so they can get a well needed drink.
Any concerns consult a qualified florist to assist.
Enjoy planning your Special Day!
Kind regards Arlene
Brizzy Bridal Bouquets