contribute aesthetically to the garden in winter. In other situations, certain
tender perennials can be left up for the winter to ensure overwintering. Margin-
ally hardy perennials, such as ‘Mönch’ aster (Aster ×frikartii ‘Mönch’), tender
ferns, and mums, benefit from leaving the old foliage on the plants to provide
insulation for the crowns during cold weather. I leave the old fronds on all ferns
until spring, whether they are tender or not, and some ferns, like the Christmas
fern (Polystichum acrostichoides), are evergreen and hold up well through the
winter regardless. An eye-opening research study out of Germany, conducted for
Yoder Brothers, showed that mums that were not cut back in autumn resprouted
substantially better and earlier in the spring than the plants that were pruned.
Many of the cultivars tested had no overwintering losses if they were not sheared
back in the fall, compared to 75–100 percent overwintering loss for those that
were sheared. Wait until warm weather is ensured in the spring to prune mums.
Another reason to not cut down certain perennials in autumn is demon-
strated by Ceratostigma plumbaginoides. This species emerges late in the spring,
sometimes as late as June in our area. I like to leave the old stems over the winter
and into the spring until the plant emerges. This way, the old stems serve as an
indicator that something is growing there, ensuring that the soil isn’t disturbed
or something else isn’t planted in its space while it’s taking its time awakening
from the winter.
On the flip side of all these reasons to not prune in the autumn, there are many
reasons why pruning is necessary before the coming of winter. One important
reason to cut certain perennials back is to avoid overwintering diseases or
insects. Some notable examples include fourlined plant bug and mildew on
monarda and other members of the mint family, botrytis on peonies, and borers
on bearded iris. Removing foliage and stems of these plants from the garden in
the winter can help reduce maintenance problems for the following year. In
addition, removing excessive debris such as fallen leaves and fallen deadheads
decreases other potential sites for pests. I recommend raking large leaves of
maples or sycamores out of the garden in autumn, as these can mat down and
hold water, contributing to the potential for crown rot on the perennials. Also, if
large quantities of leaves litter the garden, most of them should be removed. It’s
not practical to get every leaf out—and what a bore it would be to try—but too
many can be a problem.
Besides pruning in autumn to minimize the incidence of pests and disease,
there are aesthetic reasons to prune before the coming of winter. Some perenni-
als simply do not contribute much to the winter garden; in fact, they may detract
from it. In such cases I opt to cut the plants down. This might include veronicas
or geraniums that have blackened and turned to mush, or a great coneflower
(Rudbeckia maxima) that has fallen onto a frequented path. Certain ornamental
grasses are better cut down before the winter because they either break down in
the winter or lose their good color. If a grass is not reliably hardy, it should be left
unpruned for the winter.
The pruning done during the growing season can dictate whether a plant
needs pruning in the autumn for winter. Many perennials cut back during the
growing season remain as attractive, low green mounds into the winter. For
example, if Centaurea montana is pruned back in the summer and all that
remains is fresh low basal foliage in the autumn, it doesn’t need to be pruned
again for the winter. On the other hand, if the plant was not cut back heavily
during the season, the tall stems and leaves will blacken and require pruning in
late autumn. Also, if a perennial is deadheaded during the season, so reseeding
is not a concern, the rest of the plant may be able to remain for the winter. If the
plant wasn’t deadheaded, it may be best to cut the entire plant down before
winter to avoid reseeding, rather than deadheading at this point.132 PruninG Perennials