Taken from Eclectic Gardener @ http://www.teachinggarden.org/
Written by Alan Hickman

With September staring us in the face, most people are turning their attention indoors and, if they think of the garden at all, the prospect of raking leaves is what comes to mind. For others the return of crisp early morning air and perceptibly shortening days mean that the there are three more months of good gardening yet to come.
When the CNE has closed and the kids are back at school, that is the time to start fixing the mistakes, filling the gaps, and pushing the boundaries of the perennial garden.
The pressure is off, the soil is still warm and, if you have to water, the moisture is not sucked out by blazing heat and searing wind. Even better, if you need to shop, garden centres are no longer packed like cattle yards on sale day. With the departure of the crowds most of the hype has also gone. There are no campaigns pushing this miracle concoction or promising that some new and improved wonder bloom will transform a weed patch into a tropical paradise.
As a more useful aid for deciding what to plant in the fall, one might do much worse than look at the recommendations of the Perennial Plant Association. Every year beginning in 1990, association members have selected one plant which, over time, has proven to be an outstanding performer in its class. Some of these plants were introduced more than fifty years ago and they are all easily grown in a wide variety of garden situations.
One great advantage of the PPA list is that it is short - just seventeen plants so far. With some planning, even a quite modest garden could accommodate all of the selections. For someone starting a new perennial garden, the listed plants would provide a varied and solid foundation to build on in subsequent years.
The Perennial Plant of the Year for 2006 is a cultivar of one of my favourite species. Dianthus gratianopolitanus ‘Feuerhexe’ - ‘Firewitch’ in English. The species is a favourite in part because of its wonderfully over-the-top name. Gratianopolitanus is everything that some people find intimidating about botanical names. It’s long and clunky and completely unfamiliar. On the other hand, once you can reliably get your tongue around it, if you can work Dianthus gratianopolitanus into a conversation lots of people can be gulled into thinking that you really know something! The word means simply ‘of Grenoble’.
The favourable garden qualities of the cultivar ‘Feuerhexe’ include; cold hardiness - USDA zone 3 - and heat and drought tolerance. The clove scented, purplish pink, flowers come in profusion in late spring and, if the spent blooms are cut off, the plant will likely re-bloom later in the season. Nirvana for these plants is full sun and an open gritty soil or a south facing and fast draining bank..
Generally, if dianthus have an Achilles heel it is excessive moisture. The plants will drown and rot very quickly if there is any standing water and this is especially the case in late winter and early spring
While ‘Feuerhexe’ is a low growing, mat forming, plant for the front of the border, the 2001 PPA selection, Calamagrostis × acutiflora ‘Karl Foerster’, is a bold background or accent plant. This is a clump forming ornamental grass which reaches a height of about 5 feet and a diameter around 18 inches. These plants are growing in the nursery beds and in the Wedding Garden at the Brampton Fairgrounds and they are really tough customers. Despite winter’s rain, hail, snow, and battering winds, the stalks stand tall and unbroken until they are cut down in early spring. The cultivar does not have invasive roots and, being sterile, it does not scatter adventitious seedlings hither and yon.
A PPA selection which is presently in bloom in the nursery garden is Phlox paniculata 'David'. This 2002 choice is a cultivar of native Phlox paniculata plants rescued and preserved by volunteers of the Brandywine Conservancy, near Philadelphia, in the 1980s.
One particular seedling stood out because of its fragrance and apparent resistance to powdery mildew. Under the name ‘David’, this selection was subsequently propagated commercially. Research at the University of Vermont and at Cornell University has confirmed the cultivar’s superior resistance to mildew and has demonstrated cold hardiness to USDA zone 4. ‘David’ is an erect perennial, growing to a height of something over three feet, with white flowers which Hydrangea blooms.
For a full list and descriptions of Perennial Plant Association selections see http://www.perennialplant.org/