zone 4? northern ky i have flower beds in front of front porch (newly repainted black base with white pillars) a large boxwood reigns there. (3 1/2 ' x 3 ft approx!) i am redoing beds due to neigborhood cat interest.will be building up soil and small rock wall. ive already run into roots of said boxwood. i have a daisy doing ok and just planted delphinium (not doing that well) and penstemon. also have moonbeam coreopsis. please advise perennial suggestions!? maybe salvia? something that fills area quickly but won't mind roots of boxwood? thank thank thank you...