In the Garden:
Ornamental grasses add interest to the winter garden if not cut back until early spring.
To Cut or Not to Cut
That is the question -- the one you ask yourself in the fall as you survey your flower garden, pruners in hand. Which perennials should you cut back and which should you leave standing? Although your initial impulse may be to cut all your herbaceous plants back to tidy things up when the weather turns cold, leaving the tops of some plants in place over the winter can add interest to an otherwise bleak landscape and provide food for seed-eating birds. It can also help some plants make it through the winter more reliably. But there are also good reasons for cutting back certain perennials as soon as their tops are killed by frost. Here's some advice on when to wield your clippers and when to wait.
Add Winter Interest
Some perennials that grace the garden with beautiful blossoms early in the season continue to enliven the garden with their interesting seedpods in fall and winter. Baptisia's elongated black seed pods stand out against the snow, as do those of Siberian irises, and both are useful in dried arrangements indoors. The dried flower heads of yarrow (Achillea) add a horizontal note, while plants such as 'Autumn Joy' sedum and Joe Pye weed (Eupatorium), with large, rounded flower clusters, remain as lacy globes over the winter.
Ornamental grasses are some of the most dramatic plants in the winter landscape. Tall plumes feather reed grass (Calamagrostis) and switch grass (Panicum) add vertical accents to the winter landscape. Just be sure to cut plants back in early spring before growth emerges to avoid damaging the new shoots.
Benefit Birds and Butterflies
Goldfinches and other feathered visitors will stop in winter to dine on the seedheads of plants such as black-eyed Susan (Rudbeckia), heliopsis, and purple coneflower (Echinacea). The seedheads of many annuals will also provide treats for passing birds if blossoms are allowed to go to seed and remain through the winter. Cosmos, coreopsis, bachelor's buttons, and zinnias are some of the flowers whose seeds will feed sparrows, finches and juncos. But do keep in mind that plants like rudbeckia and purple coneflower may self-sow enthusiastically and you'll need to be prepared for some ruthless weeding come spring if you let their flowers go to seed.
Perennials left standing can also provide spots for butterflies and other beneficial insects to overwinter, either as pupae, caterpillars, or eggs, and offer them cover from predators like birds and spiders.
Offer Cold Protection
Some perennials are more likely to survive winter's cold if they aren't cut back until spring. Frikart's aster (Aster frikartii), Montauk daisy (Nipponanthemum nipponicum), chrysanthemums, agastache, and red hot poker (Kniphofia) all benefit from the insulation that the old foliage provides to the crown of the plant.
Leave Basal and Evergreen Foliage
And finally, there are those plants that produce a clump of new basal leaves late in the season, like Shasta daisies and globe thistle. You can cut down the spent taller growth or bare flower stalks, but leave the basal foliage undisturbed. Also, don't cut back low-growing evergreen or semi-evergreen perennials, like some hardy geraniums, heucheras, hellebores, dianthus, and moss phlox. These can be tidied up in the spring, if need be.
Mark Late Sprouters
A few perennials are notorious for their late emergence in spring. If you leave at least a portion of the tops of butterfly weed (Asclepias tuberosa), rose mallow (Hibiscus moscheutos), and balloon flower (Platycodon grandiflorus) standing, you won't lose track of their location and accidentally damage them by digging into them before they sprout in spring.
Daylilies look pretty raggedy by the end of the season. They don't add anything visually to the winter garden and getting rid of their browning foliage and bare flower stalks improves the appearance of the landscape. The foliage of other plants, such as brunnera and veronica, turns black and becomes mush after its been hit by frost and from an aesthetic standpoint is best removed. I've also found that it's much, much easier to cut down the tops of plants that don't have tough leaf stalks, like daylilies and Siberian irises, when they are still relatively crisp and upright in the fall. By spring their leaves have become a fallen, sodden clump that can be a real challenge to cut away.
The tops of some perennials, such as bearded iris, peonies, bee balm, and garden phlox, often serve as reservoirs for overwintering insects or disease spores and are best cut down and consigned to the trash or sent to a municipal hot composting operation. It's a good idea to cut back and destroy any disease-infected or insect-infested plant debris. When I'm not sure if the pest organism overwinters in or on plant material, I err on the side of caution and get rid of it.
What About the Rest?
For many other perennials, it's up to you whether to cut back now or in spring. You'll offer the most benefits to wildlife if you leave the most plant material standing until spring. But spring is also a very busy time for most gardeners and you may choose to take advantage of the slower pace and pleasant weather in autumn to get at least some of your garden clean-up chores out of the way.
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