If sibling rivalry were found among plants, it probably would be among the salvias in the large mint family (the Lamiaceae). In my opinion, ‘Mystic Spires’ wins the competition, hands down.
Four popular cultivars of blue-flowered salvias are crosses between mealycup sage, Salvia farinacea, and a large Mexican salvia, Salvia longispicata. The oldest family member is ‘Indigo Spires,’ the result of an “unplanned birth” (natural cross-pollination) in Indiana in 1979. This 4-foot-tall, lanky firstborn resembles its S. longispicata parent. ‘Mystic Spires Blue’ (‘Mystic Spires’ for short) is a mutant (literally) of ‘Indigo Spires’ produced in a California laboratory in 2003. It grows at least 2 feet tall, not counting the flower spikes.
Next came ‘Rockin’® Playin’ the Blues’® (‘Playin’ the Blues’ for short) in the 2010s. This sibling was the fussy one in my yard and is probably best suited to pots, not in-ground culture. The newest and shortest offspring is ‘Mysty,’ available since 2018. Only 12 to 18 inches tall like its mealycup sage parent, ‘Mysty’ has sturdier stems, larger leaves, and longer flower stalks.
All four salvias in this group bloom well in part sun, which is about 6 hours of sunlight per day. ‘Mystic Spires’ also blooms in part shade with just 4 hours of sunlight per day. This cultivar is more reliably winter hardy in USDA Growing Zone 8 than ‘Indigo Spires.’ It may even be evergreen in a sheltered spot, such as next to a brick façade or wall. ‘Mystic Spires’ blooms from mid-May in the coastal plain until the first hard frost. Plants usually keep their lower leaves and look full and lush all year.
‘Mystic Spires’ is a hardy perennial that adds intense royal blue color to beds and borders.
For more information on salvias, see HGIC 1174, Salvia.