I used to smoke - quite heavily most of the time and never more so
than when sitting in front of this screen. To my side is a corner
group of plants - Howea, Dysis & Dieffenbachia and for many years
their pots have served as impromptu ash trays from time to time. The
plants have grown well despite this 'abuse' and continue to thrive.
There's very little in the ash - either harmful or useful and usual
analyses show traces of calcium, iron, magnesium plus other elements.
The quantities involved are so small that they present no risk nor do
they offer any benefit so from a plant's perspective they are
essentially inert. Don't worry about the rose, any problems will
certainly not be due to cigar/cigarette ash.