Answer: You can if you wish, however the plant doesn't need to be trimmed, other than for aesthetic reasons. If you do trim, it is best to trim it back in late winter, before the new growth comes out. That way the new growth will not have cut, jagged tips. Use a mower to cut the old liriope back to the ground.
You can still cut the liriope back and it will regrow fine. You will just have some jagged tips when it does.
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