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More on Fall Gardening Chores
by Heritage Perennials
October 26, 2008

Last month we talked about waiting a bit longer before cutting things back, and suggested that early fall is a good time to plan ahead and make notes on improving your garden design next season. Depending on where you live, sometime in the next two months it will indeed be good timing for some autumn cleanup. I like to wait until a couple of hard frosts have hit the tops of perennial before cutting anything much back. Doing it too early can lead to a new burst of growth during fall warm-spells, and this is something to avoid. It's far better to wait a bit and let the plants think about shutting down for winter in their normal way. 
Again, to those new gardeners out there, it is worth stressing that you may consider doing a minimum of cutting back the first fall or two, until you figure out which perennials have good winter interest. Winter interest is entirely subjective, and only you can decide what is attractive to your eye, or what looks tired and messy. Here are a few tips and ideas:

  • fall-blooming ornamental grasses usually remain gorgeous well into the winter. It seems a real shame to cut them back to the ground before late winter or early spring. Some gardeners are now waiting even beyond THAT, and enjoying the effect of wheat-colored grass clumps contrasting with spring-flowering bulbs!

  • seed-heads of certain perennials provide food for finches and other birds, and they look great against a blanket of snow. Most late-flowering daisy-type perennials are on this list (like Rudbeckia and Purple Coneflower), but others with nice seed-heads and sturdy stems include: Achillea, Agastache, Aster, Astilbe, Baptisia, Buddleia, Chelone, Cimicifuga, Eryngium, Eupatorium, taller Sedum, and a few others.

  • there is a common theory th! at the dead tops of perennials help to trap the snow, which is the very best insulation against cold temperatures. In regions with erratic snowcover and mid-winter thaws, the tiny bit of extra snow that is actually trapped may in fact be of little benefit.

  • many perennials have very little winter interest. Cutting these types back in the fall effectively "clears the clutter" and makes the ones you leave look even better. Consider cutting these down in late fall: Alchemilla, Anemone, Campanula, Centaurea, Coreopsis, Delphinium, Dicentra, Euphorbia, Geranium, Hemerocallis, Hosta, Lychnis, Monarda, Nepeta, Oenothera, Phlox (tall types), Trollius, Veronica.

Certain perennials naturally carry over a low clump of evergreen leaves near the ground, known as a "rosette". Although you can trim the upright stems back, ! these lower leaves need to be left alone in the fall. By spring they often look a little worse for wear, but a quick trim with scissors (only the brown or dead parts) will tidy the plants up again. In this group are: Achillea, Aster, Coreopsis, Digitalis, Erigeron, Fragaria, Gaillardia, Geum, Heuchera, Bearded Iris, Shasta Daisies, Penstemon, Poppies, Polemonium, Potentilla, Salvia, Scabiosa, Stachys, Tiarella, Verbascum, and many of the hardy ferns. 
Evergreen perennials and alpines should not be trimmed in the fall. Usually the best time to trim these is immediately after blooming, if at all. Leave these ones alone in the fall: Ajuga, Alyssum, Arabis, Armeria, Artemisia 'Powis Castle' and 'Huntingdon', Aubrieta, Aurinia, Bergenia, Cerastium, Corydalis, Dianthus, Epimedium (trim in late winter, before new buds appear), evergreen Euphorbia, Helianthemum, Helleborus, Heuchera, Iberis, Kniphofia, Lamium, Lavender, Liriope, Origanum, Phlox (creeping types), Primula, Pulmonaria, Sagina, Saxifraga, Sedum (many creeping types), Sempervivum, Teucrium, Thymus, Viola. 
Certain woody-stemmed perennials are better left alone in the fall, and pruned back in the spring, leaving about 6 inches of woody stem for the new buds to appear from. These include: Buddleia, Caryopteris, Erysimum 'Bowles' Mauve', Fuchsia, Hypericum, Lavatera, Perovskia (Russian Sage), Phygelius, Santolina. 
And, finally, certain perennials with associated disease or insect problems should not only be cut back in the fall, but care should be take! n to remove and destroy the leaf litter below them, where insects and pathogens may be hiding. Among these: Alcea (Hollyhocks), Aquilegia (Columbine), Crocosmia, Delphinium, Helenium, Heliopsis, Hemerocallis (Daylily), Iris (Bearded types, leave green leaves alone but remove all dead ones), true Lilies, Monarda, Peonies, Summer Phlox, Tricyrtis, and Veronica (tall types).

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