Grasses really come into their own at this time of year: the arching stems of Stipa gigantea have turned a deep golden brown and are full of airy movement, tall columns of Calamagrostis x acutiflora ‘Karl Foerster’ stand out against the evergreen hedge, and the wispy seed heads of Molinia caerulea subsp. October is a good month to divide clumps of perennials that have become overgrown: fast-growing, thuggish plants such as Phlomis russeliana and Cephalaria gigantea need dividing every other year (and seedlings removing); other perennials benefit from being divided every three to four years to keep them vigorous but under control.