Penns Creek Cascade is Grande x wallisii. longifolium is a total weed and loves water, and its hybrids (i.e. Grande) usually are very easy-growing and do well like your average water-loving phrag. adding a shot of wallisii probably produces more cultivars that prefer to be drier, although I would imagine that most cultivars are still easy-growing and would do well with copious water. But that should be evaluated on a case-by-case basis; if you are using something water-retaining like s/h and you see lots of fat roots, no need to change.