Sometimes what seems like grass is another plant in disguise. Although liriope (Liriope spp.) , also referred to as monkey grass, is considered a border grass, it is botanically a part of the lily family. So if you use a grass-specific herbicide to destroy true grasses in your garden, then the liriope grass lookalikes are unaffected.
Liriope Species
Both main liriope species have different growth habits and hardiness ranges. Liriope muscari, commonly called big blue lilyturf, is a perennial in U.S. Department of Agriculture plant hardiness zones 5 through 10. Liriope spicata, commonly called creeping lily turf, is hardy in USDA zones 4 through 10. As its title implies, creeping lilyturf includes a spreading habit that can become invasive. It multiplies by rhizomes that creep just under the ground surface, forming a dense underground network. Blue lilyturf is controlled, with a clumping habit that makes it acceptable as a edge for sidewalks, flower beds or garden islands.
Killing the Grass
Herbicides that destroy grass are discerning — targeting grasses just — or non-selective — killing most vegetation, irrespective of type. Grass killers that are safe for liriope are selective herbicides that target true grasses. The brand names vary, however, the effective chemicals have names like fluazifop-P-butyl and sethoxydim. Some grass-selective herbicides are premixed, but others need diluting in water, typically at the rate of approximately 3/4 oz to 2 ounces of chemical per 1 gallon of water. These grass-specific herbicides will not harm liriope, even if the chemicals are sprayed directly on it.
Leaving the Well-behaved Liriope
Grass may invade a clean liriope edge, producing the need to remove it while leaving the liriope intact and unharmed. After spraying a grass-selective herbicide on the grass that grew into the liriope, kill the grass in a 6- to 12-inch-wide buffer strip between the liriope border along with your lawn. Mulch this buffer zone to suppress the weeds and grass. You can also install plastic edging at the grassy side of this buffer zone to help maintain a specified border between the yard and the liriope.
Controlling the Ill-mannered Liriope
Liriope spicata isn’t acceptable as a border plant, but it excels as a ground cover to naturalize a large region and help control erosion. If you would like to dominate Liriope spicata that has overgrown its boundaries, spraying a grass-selective herbicide on it won’t work. First, use a shovel or tiller to dig till up the plants, and make use of a rake to eliminate as much as possible. When new development inevitably looks, spray it with a non-selective, ready-to-use herbicide, like one that’s glyphosate as the chief chemical. After fourteen days, spray again, and repeat as often as required.