Perennial Care After The First Freeze
We suggest cleaning up your perennials in the fall or late winter to prepare them for their debut in spring. Doing so prior to new growth appearing will ensure the plants look and perform their best. Many perennials die back after the first hard freeze and seem to just disappear. (Day lilies, Cannas, etc.) It will show up as blackened leaves as the affected tissue dies over the next few days, loss of flowers if it was blooming and change ornamental grass from green to a straw color. Ornamental grass needs trimming yearly before the growing season begins. Liriope and some vining ground covers will also require trimming.
How to trim:
The softer, tender perennials that died down can be removed if desired or allowed to decompose naturally and then clean up a bit in spring.
Woody based perennials should be cut back to 6-10 inches high. They will grow fuller and become more compact plants without all of the old woody growth.
You can cut back the affected liriope and mondo grass for cosmetic reasons now or wait until mid-February. Not everyone chooses to do this and it isn’t a necessity. It will help the plants come back easier in spring though. You can use your lawn mower set on a high setting or a weed eater to make the job easier. If trimming, make sure to do it by mid-February since late trimming will cause ragged tips on the new foliage.
The toughest job is trimming ornamental grasses and I usually wait until mid-February to tackle this. I leave the straw colored grass untrimmed so I still have a plant in my landscape. (A How-to on cutting ornamental grass can be found here.)