There are a wide variety of Michelmas Daisies available as Aster novi-belgii isn't a species as such, but a group of hybrids.
They vary in size from 10cms to 1.8m in height but all share the same overall impression of forming a bushy clump of mid green foliage over which are held a profusion of open faced, daisy like flowers in a variety of colours.
They are perfect for borders and due to size variations can either go front, middle or back to good effect.
They also make excellent cut flowers and as they are perennials you can cut them back after flowering in late autumn and they will flower again next season.
Any well balanced cottage garden will feature Michelmas Daisies, especially in borders.