Monthly Archives: November 2021

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.