I want to make some mums for a cake this weekend. I don't want them out of royal icing, so my question is how do I get the buttercream mums off the flower nail onto the cake?

You can use a flower lifter (like you would for a rose). If you do it on wax paper on your flower nail, take the the flower off with the wax paper and make a whole buch and stick them in the freezer. Once frozen, you can quickly pick them up with your hands and place them on the cake.

I airdry mine on wax paper and then place them by hand on the cake.

Thanks ladies that helped a bunch. After I posted my question I guess I had a lightbulb moment because I made some and decided to freeze them.

I use a very sharp paring knife and slide it under the flower either right away or after it dries a little. Then I can slip it on to the cake where I need it.

Great advice given from all.... one other thing you may want to watch for, though, is when you take the mums out of the freezer, you may want to unwrap them (or take them out of their container) and put them in the fridge for a bit. If you get condensation on them when going from the freezer right to the cake, the color can bleed onto the cake.... just a thought.