For best performance, plant perennials in well-amended soil; dig the soil at least 8 inches deep and amend it with 2 or 3 inches of compost or well-rotted manure. Knock the plant from the nursery pot and loosen any coiled roots. Position plant, firming soil around it. Fertilize lightly three times during the bloom season and water regularly (when stressed by lack of water or nutrients, plants tend to force a quick, weak bloom then stop flowering for the season).
Support. Many tall perennials need help standing up straight; the trick is to avoid a lot of visible hardware. Sometimes you can plant tall, weak-stemmed perennials between woody perennials or shrubs that serve as subtle supports. For a few tall stems, it's simplest to use bamboo or metal stakes; keep ties loose. For larger, multibranching plants, set hoops in place when planting, or use linking stakes later to corral long stems.