How to Thin Out Monkey Grass

Monkey grass grows quickly and can produce large clumps that are unattractive, depending on the variety. The only way to thin a monkey grass clump is to dig it up and divide it, but each division will grow into another large clump in time.

If you find that your monkey grass (either ‌Liriope‌ spp. or ‌Ophiopogon‌ spp.) regularly develops clumps that you find too large, consider replacing it with a smaller, less vigorous variety, such as a dwarf cultivar. If you are growing the invasive species ‌Liriope spicata‌, you may want to remove it entirely.

Choosing a Monkey Grass Variety

Confusingly, the term “monkey grass” describes several kinds of clumping plants that are not actually grasses but part of the lily family.

Those most available in nurseries are usually ‌Liriope muscari‌, also called giant lilyturf, or ‌Ophiopogon japonicus‌, also known as dwarf lilyturf and mondo grass. These grasses all clump and are valuable landscape additions, working well as border plants and able to grow in part shade, unlike most grasses.

Here are the primary plants commonly known as “monkey grass.”

Liriope Muscari

Some common names for this evergreen plant are big blue, big blue lilyturf, big blue liriope and giant lilyturf. This is the “good” liriope because it isn't invasive.

This species, growing in USDA hardiness zones 5 to 10, makes a great edging plant, sporting dark green leaves growing in clumps of about 1 foot to 1.5 feet high and wide. ‌Liriope muscari‌ is a flowering plant that produces small purple blooms in late summer atop 6-to 8-inch stems, although the blooms are innocuous.

Ophiopogon Japonicus

Also commonly called mondo grass or dwarf lilyturf, ‌Ophiopogon japonicus‌ (zones 7 to 10) is a smaller plant than liriope muscari, reaching about 1 foot high and wide, and its leaves are a narrower, finer shape. It also produces purple flowers in summer on top of stalks.

There is a dwarf mondo grass variety (‌Ophiopogon japonicus‌ 'Nanus') that grows just half the size and might be a good option if your monkey grass is growing larger than you like.

Liriope Spicata

There is a type of monkey grass that you should not plant, and if you already have it, consider trying to remove it. This is ‌Liriope spicata,‌ which not only clumps but spreads by runners.

Also called “creeping liriope” and “creeping lilyturf” for good reason, be sure to read the tags at the garden center closely to make sure you are not purchasing this liriope plant.

Dividing Monkey Grass

Dividing monkey grass doesn't make it thinner; there is no way to prune or shape a monkey grass plant that reduces its mass. However, you can dig it up, cut the clumps into smaller pieces, and then replant at a wider spacing. This is a simple procedure.

Using a shovel, dig around the monkey grass plant and lift it out in one clump. You can use a sharp knife to slice the clump into several sections or wash off the soil and pull apart the clump, taking care to retain as many roots as possible on each piece.

Make sure the crown is planted at the same depth as it was previously growing.