Do you mean your friend wants to have flowers "materialize" like the orange tree does in the movie the Illusionist? If you haven't seen the movie, here's a clip of what I'm talking about: http://www.youtube.com/watch?v=KEvkYo30rCc
Or if you want something simpler, you could have yourself packed with artificial vines & flowers in yourjacket, vest & shirt. Have a large sheet put over him and while hidden from the audience, he could "release" all the plantation within him. You might need altered clothing to make this quick & easy. Sort of like the quick change artists.