The grounds here at the Civic Garden Center are gradually sauntering their way to bed. It’s okay; after a year like this, we’re all tired and many gardeners desire to institute a scorched earth policy in the garden. However, it is good to take a minute to assess your goals and the health of your plants before you pull out the pruners.
Regarding aesthetics, beauty is in the eye of the beholder, and while I love the look of dried grasses in the winter landscape, my neighbor may view them as messy straw heaps. Regardless, many perennials do provide some interest in the garden, especially during the ephemeral events such as snows and heavy frosts. Grasses, as I have mentioned, lend a beautiful gold to the garden, especially when growing near evergreens or interwoven with the fruit of winterberry hollies, beautyberry, cotoneaster, or hawthorns. Sedums hold their dried flowerheads upright all winter, while many of the groundcover Sedum varieties retain evergreen foliage which acquires flaming orange and red hues in the cold of winter (Sedum rupestre ‘Angelina’ and Sedum ‘Dragon’s Blood’ are great examples). Coneflowers and Rudbeckia punctuate the garden with dense, dark heads that are irresistible to birds, and Russian sage’s pure white branches are stunning. In the shade garden the spent blooms of Astilbe form cinnamon torches throughout beds where many ferns, Helleborus, and Pulmonaria can retain evergreen foliage.
For those who would rather cut back their perennials in the fall, the gardener must know that some plants should be left alone until early spring. For instance, many of your woodier perennials, such as lavender, thyme, sage, and Russian sage, should not be sheared or pruned until they start showing new buds or leaves in spring. The same is true for your butterfly bushes (Buddleia sp.) and blue mist shrubs (Caryopteris sp.). For those growing Agastache, sometimes called hyssop, cutting back in fall creates openings for rot to set in. Also, regarding chrysanthemums, things get dicey. Many chrysanthemums you buy at stores and nurseries are considered annuals by perennial experts, though they often come back from year to year. With all chrysanthemums, leave a framework of branches up for the winter and mulch over the crown with a light leaf mulch or pine bark. Once green leaves pop up in spring, pull the mulch away and cut down the dead stems.
The moral of the story is that the majority of perennials can be cut back in fall if desired and that even the pickier plants will often recover if pruned at undesirable times. However, before I start cutting, I contemplate what perennials may offer during the next three months regarding aesthetics and ecological benefits such as shelter and food for animals and insects. This requires extra discretion, but our gardens deserve to be diverse, bountiful displays of color and texture even in the dead of winter.
–Bennett O. Dowling, Horticulturist at the Civic Garden Center of Greater Cincinnati