There are no hard and fast rules about putting the garden to bed in fall. Some folks prefer to cut their perennials to the ground, while others leave them intact until spring. I take Mother Nature’s advice when it comes to fall cleanup. Perennials that turn to mush when hit by a killing frost are cut back and those who stand colorful and tall are left intact until spring.
Perennials with woody stems that should not be cut back include hummingbird mint Agastache, lavender, sage, Russian sage Perovskia and mums. The woody stems of these plants protect their crowns and help prevent winter crown rot. If you’re ambitious, these plants can be further protected in winter with a mulch of fine gravel or turkey grit. Plan to cut back mums and Agastache in spring when the basal leaves reach 3 to 4 inches tall. Sage, lavender and Perovskia also should be pruned in spring when the green buds just begin to emerge from the branches of the plants.
That’s also when I cut back my butterfly bush. However, these shrubs break dormancy later in spring, so be patient and let them get their beauty sleep.
Evergreen perennials, such as Heucheraand Pulmonaria with leaves that persist throughout the winter, should also be left intact. I tidy them up after the speckled-leaf lungworts bloom in spring
In my garden, heavy seed producers such as Malva alcea”Fastigiata,” New York asters and lady bells Adenophora are deadheaded and cut back in the fall to keep them from reseeding throughout the landscape. Old-fashioned rose of sharon is another re-seeder that was once on my must-deadhead list. I now grow new varieties that don’t set viable seed. However, the seedpods from the old-fashioned varieties are quite attractive and can be used in dried flower arrangements and Christmas decorations. They really look quite nifty when spray-painted gold or silver.
I leave flowers with attractive seed heads in place for winter interest in the garden and food for the birds. The stems and spent flower clusters on my sedum “Metrona” turn an elegant brown when hit by a hard frost, and they look great in the winter garden. I also leave the seed heads of coneflowers intact. My wild flower meadow filled with Queen Ann’s lace, goldenrod and a variety of wild grasses and flowers is stunning when frosted with snow or glazed by hoarfrost. So it gets cut back as soon as new shoots begin to emerge in spring.