My large stand of Martagon lilies in the back garden are all the variety 'Mrs. R. O. Backhouse'. In only a few years half a dozen bulbs have exploded, while the Martagons in the driveway border — the deep red 'Claude Shride' — have expanded much more slowly. The difference may be the quality of the soil, amount of sun (or lack thereof) or the degree of rainfall that reaches the different groups. I've never quite been able to determine the reason for the difference in their growth habits. Even though there's not many of them, the lacquered red of the petals of 'Claude Shride' make up in drama what they lack in volume.