Older varieties show their weakness when they turn down after flowering. Summer dormancy always limited the appeal of the genus, and it gets triggered early if the soil dries out or heats up for an extended time. The edges of the leaves will begin the crisp and the plant wilts. At this point, they stall out and go into a summer dormancy.
This is where the selection of cultivars makes a difference — newer versions flush a new set of leaves immediately after flowering, choosing to deal with the summer without shrinking away from it. This gives the new breeding a much longer garden appeal that escapes the snoozy older varieties.
Over the last couple of decades, “quality” has shifted the bar set by ‘Mrs. Moon’. Breeders now emphasize vibrant blooms over the earlier pastel colors, shorter stems that keeps the flowers tight to the leaf canopy, and thicker leaves to cut back on crisping. A major push has made most modern cultivars more resistant to heat and mildew - problems that often appears in tandem.
The best versions with the longest garden appeal were based on the longifolia species. You know them as vigorous stalwarts like ‘Diana Claire’ and ‘Raspberry Splash’. However, a French species, cevennensis, has brought exceptional drought and disease resistance to the breeder’s toolkit. It’s a strong boost for both summer appeal and southern gardens, but this innovation is new to the market. You only see it in recent introductions like ‘Silver Bouquet’.