Short answer
Cut back mondo grass in late winter or early spring, just before new growth starts. In many climates that means somewhere between late winter and early spring. The aim is to remove tattered old leaves so the fresh foliage can come up unobstructed, and to avoid cutting the new leaves, which would leave brown, blunt tips for the rest of the season.
Why early spring
Mondo grass (Ophiopogon) is not a true grass. It is a tuft-forming, evergreen perennial in warm climates, though foliage can look battered after a cold winter. Leaving the old leaves over winter gives the crown some protection, so most sources advise waiting until the worst of the cold has passed. Extension sources suggest early spring, and a gardening Q&A through the extension service says that trimming in early spring is reasonable, and that a late trim is still possible if you are careful.
How to cut back mondo grass
- Small areas: Use hand shears, garden scissors or a hedge trimmer to cut the old foliage down to a few inches above the ground. Many gardeners simply shear off the tattered tops and edges.
- Large areas: Run a lawn mower over the patch on its highest setting, with the blade raised well above the crowns. Do not scalp the plants or cut into the crown.
- Clean up afterward: Rake out the clippings and tidy the bed. A light compost mulch can help.
Cold-damaged foliage
After a hard winter the leaves can look burned or brown. If new shoots are not yet showing, a trim helps. If new leaves have already come up, trim only the old brown tips, or wait. Cutting through green growth leaves ragged ends. In cases of severe damage, the plant often recovers on its own as new growth fills in, so trimming is mainly cosmetic.
Do you need to cut it at all?
Not necessarily. Mondo grass does not require regular mowing or trimming, and many people leave it alone. A trim every year or two can help refresh a patch that looks scruffy.
Related plants
Liriope (lilyturf) is often confused with mondo grass and is cared for similarly, though it tends to be taller and coarser. Black mondo grass is a slower grower, so cut it conservatively. For other ornamental grasses, the rules are different; see cutting back ornamental grasses and our overview of ornamental grass care.
If you need to thin out or move a patch, mondo grass can be divided, with spring being the usual time. See how to divide ornamental grasses for the general technique.