When the turfgrass lawns all around it lie exhausted and brown in the summer heat, the narrow, arching, green foliage of liriope (Liriope muscari) keeps its cool. Perennial liriope, also known as lilyturf, isn't grass. In mass plantings, however, it forms a lush ground cover, with the late-summer bonus of lavender flower spikes.

Although marketed as an evergreen that is perennial in U.S. Department of Agriculture plant hardiness zones 5 through 10, lilyturf may develop brown, withered foliage during winter in some areas. That is most likely to occur when temperatures drop below minus 10 degrees Fahrenheit.

Deep cold isn't lilyturf's only enemy. In all climates, the fungal disease anthracnose may leave the plant brown and tattered. Whether cold or disease is the problem, a well-timed trim is the solution.

Timing the Trim

The best time to trim lilyturf's damaged old foliage is anytime before its healthy new foliage emerges in spring. Otherwise, you'll shave the top of the fresh growth as well as the old growth. Fall trimming of anthracnose-blemished plants -- in warm-winter climates, at least -- keeps them looking good until spring.

Cutting back cold-damaged foliage can wait until anytime between January and April, depending on when the threat of subzero temperatures subsides in your area.

Choosing Your Method

Trim a large lilyturf planting with a lawn mower; for edgings or border-accent plants, hedge trimmers are easier to manage. Hedge trimmers are also better for cutting lilyturf with sprouting leaves because the tool can cut just above the new growth.

Making the Cuts

Before mowing lilyturf, adjust the mower blades to their highest setting.

Use the hedge trimmers like a giant pair of scissors. Kneeling, hold the trimmer grips firmly, and slide the blades into the foliage 3 to 4 inches above the crowns. As you cut, keep the blades horizontal and parallel to the ground. Otherwise, the trimmed plants will look uneven and spiky.