I am fortunate to fly frequently on LH F and always get roses. My present experience is that they are mostly placed on my tray or arm rest rather than placed directly into the holder. A year ago they placed them in the holder about half the time on my flights.

Particularly on lightly loaded flights, I have seen the crew also place a number of roses in a pitcher as a bouquet decoration for the bar area on 747-400 and A340.

You ceratinly should not take them through US customs. I don't know about other countries' regulations.

Charles