18" is an accurate height for "Intermezzo." It is not a large growing plant. I have seen it in person through the years at the San Jose Heritage Rose Garden; it has never reached above my knees but is always in bloom. I cannot say with certainty whether it is a weak plant or merely a short grower. This trait was most likely passed on by its seed parent "Grey Pearl," a notoriously difficult plant to grow on its own roots or budded.