Many perennials and shrubs take well from late season semi-ripe cuttings, such as lavender, box and lilac. Insert tip cuttings into hormone-rooting powder and then compost. Water, place in frost-free environment and then only water when dry. Take root cuttings from perennials such as eryngium and acanthus, put in compost. Division is another cheap way of increasing your stock, for example achillea, aster, crocosmia, sedum and phlox.