Aster or Symphyotrichum cordifolius 'Little Carlow' is a hardy, clump forming deciduous herbaceous perennial. Abundant attractive small blue flowers cover the plant (see image) in September and October on tall stems so ideal for the back of the border. Approx. 1-1.25 m tall so ideal for the back of the border. Attractive to bees and butterflies in summer & autumn. Easily grown in any reasonably fertile soil in sun or part-shade. 
Can be grown with perennials - Rudbeckia, Helenium, Veronicastrum and Miscanthus an ornamental grass.

2 litre pot

Do not cut down in autumn! Flowers will produce fluffy pompoms full of seeds loved by seed eating birds. The tangled stems provide shelter for spiders & other insects. This provides food for insect eating birds like wrens & blue tits.