This is my first time doing a cake covered in just buttercream, then I'm going to decorate it with some fondant flowers. How do I stick the fondant flowers to the buttercream, and will they stay put on the cake? Should i let the icing crust before I put on the flowers? Should I put the cake in the fridge beforehand and afterwards? My customer is picking up the cake tomorrow, but it isn't getting eaten until Saturday, so I want it to look it's best. Thank you everyone!

Assuming your flowers are not 3-D, I dab a little vanilla extract, whatever flavor the icing is in the back of the fondant and place on the cake. I'm sure some people even use water. They will stay put regardless. You can put them on before or after the crusting. However, I would tend to put them on after the cake sets and crust. Once finished I keep my cakes in the fridge until pick up.

I use clear piping gel or a dab or buttercream.

Ok great! Thank you!

For flowers I use a dab of buttercream. If your buttercream is more shortening based it should be fine sitting out. Depending on what type flowers you are making refrigeration could cause them to be limp or soft.

Thanks for posting this questions I was about to ask the same thing!!
And of course thanks for all the replies & useful tips