B. Rosie Lerner
Extension Consumer Horticulturist
Cut Back Perennials Now
Gardeners often ask, "When is the best time to cut back the dead
tops of herbaceous perennials (stems die back to the ground each year)?"
"Should we cut them in fall as the tops fade?" "Or wait
until spring just before new growth begins?" The answers depend,
in part, on the specific plant and whether disease or insect pests are
For most healthy plants, leaving plant tops over winter is fine and, in
many respects, preferable. Many species retain dried seed heads and foliage
that may have aesthetic value. Ornamental grasses are at their best in
fall and winter.
And, if you don't cut back the tops, your native wildlife will thank you!
Seed heads, fruits, stems and foliage provide food and shelter. Although
late-season bloomers, such as brown-eyed Susans and coneflowers, may have
turned brown, birds still feed on the seed. Many butterflies overwinter
on plant debris.
Allowing plant tops to remain over winter can also help collect leaves
and snow for insulation and moisture. For some marginally hardy perennials,
like garden mums, waiting until early spring to cut back the dead tops
can actually improve a plant's chances of survival.
And, of course, leaving the tops in place will remind you where the plants
are, in case you're thinking of adding more plants or rearranging the
elements of the garden before spring growth begins.
On the other hand, plants with disease or insect pest troubles should
be pruned back in fall to reduce the chances of carryover to the following
season. Sanitation is one of the best investments gardeners can make in
reducing problems for next season. Peonies and Rudbeckia with blackened
foliage should definitely be cut back in fall. The same is true for bee
balm and phlox, which are routinely plagued by powdery mildew. Removing
iris and asparagus foliage in the fall reduces overwintering sites for
the iris borer and asparagus beetles, respectively.
Badly damaged or infested foliage can and should be removed as soon as
possible. Otherwise, wait until after several hard frosts have killed
back the tops. Cut back the tops to about two inches above the soil. Hand
pruners and hedge clippers work fine, if you have just a few plants to
cut back. But for larger plantings and large clumps of ornamental grasses,
a power hedge trimmer works well.