This is another of the many Tardiana-type seedlings of unidentified parentage originated by Dr. Ralph (Herb) Benedict of Michigan. It was registered on his behalf by Rod Kuenster of Iowa in 2010. 'Cool Blue' forms a medium size (16 inches tall by 34 inches wide) mound of intensely blue-green foliage. The thick substanced leaves are moderately cupped, moderately wavy, moderately corrugated and broadly ovate with a glaucous bloom on top. Medium lavender, striped flowers bloom from June into July.