Invasive Species Profile: Creeping Liriope or Monkey Grass (Liriope spicata)

Liriope blooms with small, purple flowers in late summer. The grass behind this specimen is another invasive weed, Japanese stiltgrass (Microstegium vimineum)

Many times when an exotic plant is introduced to a new place, people are unsure how it will fare. Will it survive here? Will it behave and remain in cultivated places? Will it escape cultivation, grow aggressively, reproduce prolifically, and become invasive? Sometimes when people see the last scenario, they think, “Great! It’s growing! I can propagate it for nurseries and make money! Nothing eats it and it resists all diseases. It has a high survival rate even when neglected, so customers will be happy that it lives and grows, too!”

This case has all the hallmarks of the species becoming invasive. There is a lag period between its introduction and becoming a full-fledged invasive weed. Though the problem with mile-a-minute (Persicaria perfoliata) was recognized within several years, normally the gap takes decades. As concerns rise about a given organism, it becomes a “species of concern” or an “early emerging invasive species.”

When creeping liriope escapes garden settings, it takes root and infests natural areas. The dense, low-growing carpet obstructs native plants, especially diminutive species and seedlings.

Creeping liriope (Liriope spicata) goes by many monikers including liriope, lilyturf, and monkey grass — a confusingly common name shared with other plants. The names implying a lily or grass are inaccurate because liriope is in the asparagus family, which include the genera, Yucca, Agave, and Hosta. Creeping liriope is an emerging invasive species from Asia. Whereas a handful of U.S. counties and municipalities declare it invasive, Arlington and Alexandria are among those recognizing it as a problematic weed that can crowd out native flora. Encountering creeping liriope in Fairfax County parks, including the Royal Lake watershed, is more frequent than it was merely 10 years ago. Spreading by rhizomes lends to the “creeping” part of its name. The roots enter natural areas by simply growing across the property line, breaking off and washing into another area, neighbors illegally dumping yard debris that contains liriope roots, or even people deliberately planting it under the false assumption that they are doing a good deed.

Azure flowers (A) adorn blue-eyed grass in the spring. The foliage lasts long into the growing season, seen here in late summer.

Throughout much of the year, creeping liriope displays narrow, dark green foliage, extending several inches to over a foot. By late summer, tiny purple flowers emerge, though they can occasionally be whitish. In autumn, small, black, ball-like fruits replace the flowers along the stalks. While some references state that wildlife may consume and scatter the seeds, water motion and foot traffic are the more frequent modes of dispersal. With few diseases or herbivores keeping it at bay, liriope root fragments and seeds start growing where they please. Since liriope is hardy and cheap, it is over-utilized in landscaping projects by both contractors and private residents, thereby furthering its coverage. Creeping liriope is a frequent find at plant swaps since people inevitably end up with more than they want. However, sharing an invasive weed is not friendly and neighborly. It is an affliction in landscapes and natural areas. Countless gardeners who thought creeping liriope would be a good, easily controlled addition to their plot ended up regretting planting it. What was supposed to be a low-maintenance plant proved to be too much work in corralling this weed.

Blue wood sedge is a Carex species that thrives in gardens.

Instead of creeping, some liriopes form clumps, such as a variegated variety and L. muscari, but these liriopes are also on invasive watch lists. Furthermore, mislabeling amongst the species at nurseries is a problem, especially when they share common names. A sure way to avoid the liriope conundrum and beautify the yard is by planting native alternatives. Stout blue-eyed grass (Sisyrinchium angustifolium), which is related to irises, blooms in the spring and keeps its low, upright foliage throughout the year. Many sedges fit the bill with short-standing blades during the growing season, such as Pennsylvania sedge (Carex pensylvanica) and blue wood sedge (C. flaccosperma). Christmas ferns (Polystichum acrostichoides) make lovely evergreen borders, especially in shade to partly sunny locations with dry to moist (not wet) soil. For every invasive weed, there are a vast number of healthy native choices available.

More information on creeping liriope:

https://mgnv.org/2020/09/30/invasive-plant-factsheet-creeping-liriope-liriope-spicata/
https://plants.ces.ncsu.edu/plants/liriope-spicata/
https://www.fairfaxcounty.gov/parks/sites/parks/files/assets/documents/nature-history/greenspring/infosheets/orngrass.pdf

Good Alternative Species: stout blue-eyed grass (Sisyrinchium angustifolium), Pennsylvania sedge (Carex pensylvanica), blue wood sedge (C. flaccosperma), Christmas fern (Polystichum acrostichoides)

Author Greg Sykes is an Invasive Management Area leader for the Fairfax County Park Authority.

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About Fairfax County Park Authority

About Fairfax County Park Authority HISTORY: On December 6, 1950, the Fairfax County Board of Supervisors created the Fairfax County Park Authority. The Park Authority was authorized to make decisions concerning land acquisition, park development and operations in Fairfax County, Virginia. To date, 13 park bond referenda have been approved between 1959 and 2016. Today, the Park Authority has 427 parks on more than 23,000 acres of land. We offer 325 miles of trails, our most popular amenity. FACILITIES: The Park system is the primary public mechanism in Fairfax County for the preservation of environmentally sensitive land and resources, areas of historic significance and the provision of recreational facilities and services including: • Nine indoor RECenters with swimming pools, fitness rooms, gyms and class spaces. Cub Run features an indoor water park and on-site naturalist • Eight golf courses from par-3 to championship level, four driving ranges including the new state-of-the-art heated, covered range at Burke Lake Golf Center • Five nature and visitor centers. Also nine Off-Leash Dog Activity areas • Three lakefront parks including Lake Fairfax, Lake Accotink and Burke Lake, with campgrounds at Burke Lake and Lake Fairfax. The Water Mine Family Swimmin’ Hole at Lake Fairfax, Our Special Harbor Sprayground at Lee as well as an indoor water park at Cub Run RECenter • Clemyjontri Park, a fully accessible playground in Great Falls featuring two acres of family friendly fun and a carousel, as well as Chessie’s Big Backyard and a carousel at the Family Recreation Area at Lee District Park • An ice skating rink at Mount Vernon RECenter and the Skate Park in Wakefield Park adjacent to Audrey Moore RECenter • Kidwell Farm, a working farm of the 1930s-era at Frying Pan Farm Park in Herndon, now with historic carousel • Eight distinctive historic properties available for rent • A working grist mill at Colvin Run in Great Falls and a restored 18th century home at Sully Historic Site in Chantilly • A horticulture center at Green Spring Gardens in Annandale • Natural and cultural resources protected by the Natural Resource Management Plan and Cultural Resource Plans, plus an Invasive Management Area program that targets alien plants and utilizes volunteers in restoring native vegetation throughout our community • Picnic shelters, tennis courts, miniature golf courses, disc golf courses, off-leash dog parks, amphitheaters, a marina, kayaking/canoeing center • Provides 263 athletic fields, including 39 synthetic turf fields, and manages athletic field maintenance services at 417 school athletic fields. PARK AUTHORITY BOARD: A 12-member citizen board, appointed by the Fairfax County Board of Supervisors, sets policies and priorities for the Fairfax County Park Authority. Visit https://www.fairfaxcounty.gov/news2/social-hub/ for Fairfax County Government's Comment Policy.

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