Can carnations be made out of buttercream? If so do they have to be made on the nail or directly on the cake?

Here are the instructions:

http://www.wilton.com/decorating/basic/carnation.cfm

Thank you but I actually had the mum in my head? I need to learn my flowers. Had my 2nd class of class II the other night talk about a brainoverload! So many flowers to learn!! I am trying to figure out what I am going to do for my cake presentation next week!?!?!