As long as more moderate fall weather persists and the soil is still workable, we can continue to tidy up and even forge ahead in the perennial garden. Gone is the more frantic pace at which we must work during the growing season, replaced instead by a more laid back, even philosophical, attitude with time to think and plan and even dream a little about the growing seasons to come.
Start by removing any dead flower heads you missed earlier, especially those of garden phlox. A few of mine are still sending out occasional blooms. They will self-seed mercilessly, their offspring an unappetizing, vigorous, magenta strain and you will find yourself weeding them out most of next year.
Cut back flower stalks of such late blooming beauties as obedient plants, boltonias, asters and mallows after the blossoms have faded. You may want to leave the more attractive seed heads like those found on ornamental grasses, sedum ‘Autumn Joy’, and coneflowers (a moderate self-seeder and good bird food) for winter interest.
Next, remove any diseased foliage. This includes mildewed leaves on asters, phlox and beebalm, botrytis on peonies, and leaf spots on delphiniums and irises. Do not compost any diseased materials unless you have a hot compost pile. Rather, bag them and put them out with the trash.
Most perennials die back to the ground with new growth arising from the crowns come spring. Even if the whole stem has died, however, I like leaving 5 or 6 inches intact for leaves to collect around as a winter mulch.
This is especially important for shallow-rooted perennials like mums and marginally hardy ones such as plumbago and goldenstar. A few perennials including hellebores and epimediums keep their foliage long into the winter and are best left to their own devices except perhaps for a light mulch.
Pluck any late germinating or persistent weeds as you go through the garden. If you are using a shredded bark or shredded leaf mulch, replenish it in areas where it has worn thin. Gardens can still be edged as long as the soil is not too wet.
Likewise, if you are planning on expanding, you can remove the sod from new areas to make your job quicker next spring.
Test the soil and work in a slow release source of phosphorus, like bonemeal or rock phosphate, and potassium, such as greensand, if your report comes back deficient in these elements.
Limestone may also be called for as a source of calcium and to raise the pH for perennials that do not grow well in acid soils.
The final mulching for winter protection should not be done until the ground freezes which usually doesn’t occur until December. If put it down too early, voles may take up residence and feast on your perennial plants all winter.
Many plants do just fine with little or no protection, but just in case we have a very cold winter I do put a nice covering of leaves or a few evergreen boughs over my most recently acquired perennials (the ones I got on sale last weekend!) as well as a few marginally hardy double primroses. The winter mulch will help prevent heaving following freeze/thaw cycles.
If you have a few blank spaces in the garden, there is still time to tuck in a few spring flowering bulbs.
Review this season
This is a good opportunity to reflect on your perennial garden’s performance.
Are you happy with the color scheme or would you like it to be more monochromatic or diverse?
Are some plants particularly prone to disease problems? Consider not growing those species affected or seeking out disease-resistance cultivars.
Are there too many plants in need of constant division? Perhaps they should be replaced with better behaved sorts.
Make some notes of what changes you’d like to make. Over the winter, use the soon-to-be-released 2010 plant and seed catalogs, along with some gardening books to guide you in selecting just the right combinations of plants for your perennial garden.
If you need help with perennial selection or have questions on any other home and garden topic, call the UConn Home & Garden Education Center (toll-free) at (877) 486-6271, visit www.ladybug.uconn.edu, or get in touch with your local Cooperative Extension Center.
Posted Nov. 8, 2009