Creeping grasses are notoriously difficult weeds to manage in any lawn or garden setting. These aggressive plants spread quickly and often outcompete desired vegetation, requiring consistent effort to control. The difficulty in eliminating them stems from their unique and robust reproductive structures. This guide provides a comprehensive approach to identifying, removing, and preventing the return of these persistent invaders.
Understanding the Grass’s Spread
The spread of creeping grasses is attributed to specialized stem structures known as stolons and rhizomes. Understanding the difference between these two types of growth is important because it dictates the most effective removal strategy. A stolon is a horizontal stem that grows along the soil surface, producing a clone of the original plant at its tip or nodes. Examples of grasses that use stolons include Centipede grass and St. Augustine grass.
A rhizome is a modified, horizontal stem that spreads underground, often just beneath the soil’s surface. These structures strike new roots downward while shooting new stems upward, allowing the grass to pop up unexpectedly in new locations. Bermuda grass and Zoysia grass are common examples that utilize both stolons and rhizomes, making them particularly difficult to contain. Simply pulling the visible leaf blades is ineffective because the main reproductive structures remain hidden, storing energy and ready to sprout new growth.
Non-Chemical Removal Strategies
Physical and environmental manipulation offer effective solutions. One method is smothering, which involves blocking sunlight to prevent photosynthesis. This technique uses materials like cardboard or thick plastic sheeting covered with four to five inches of mulch. Overlapping the edges of the covering prevents the grass from finding gaps and should be left in place for several months to ensure the grass is completely starved of light.
Solarization is a technique that uses heat to sterilize the soil, killing both the grass and seeds in the upper layers. To solarize an area, first mow the grass as short as possible and water the soil deeply. Next, cover the area with a clear plastic tarp, typically two millimeters thick, securing the edges so the plastic rests directly on the soil to trap heat effectively. This greenhouse effect can raise soil temperatures to above 140 degrees Fahrenheit in the top six inches.
Solarization is most effective during the hottest part of the summer, requiring four to six weeks of full sun exposure. While this method controls aggressive varieties, it may require multiple attempts to eliminate deeply rooted rhizomes. For mechanical removal, thorough digging is necessary to ensure all rhizomes and stolons are fully extracted. Since even small fragments can regenerate, the soil should be carefully sifted to remove all pieces of the underground stems.
Using Herbicides for Control
Chemical control requires careful selection and application. Herbicides are broadly categorized as either selective or non-selective based on their target. Selective herbicides are formulated to target specific weeds, such as broadleaf weeds or certain grasses, while leaving a desired lawn unharmed.
Non-selective herbicides, such as those containing the active ingredient glyphosate, will kill all green vegetation they contact, including the desirable lawn. These are typically used for clearing entire areas like garden beds, driveways, or when preparing a site for new landscaping. Since creeping grasses are biologically similar to turf, killing them within a lawn often requires a specialized selective herbicide, which may require multiple applications over several seasons for complete control.
Application timing is important for maximum effectiveness. Herbicides work best when the grass is actively growing, typically in the spring or fall, as the plant actively absorbs the chemicals. Always read the product label to ensure the chemical is safe for the existing turf and to avoid application during high temperatures, often exceeding 85 degrees Fahrenheit, which can damage the lawn. Applying herbicides on calm days prevents wind from carrying the chemical drift onto desirable plants in nearby areas.
Maintaining Boundaries and Preventing Recurrence
Eliminating creeping grass is only the first step. Healthy, dense turf is more resistant to weed encroachment because it crowds out new invaders and shades the soil. Mowing the desired turf at the highest appropriate setting, often three inches or more, helps to shade out the low-growing runners of creeping grasses.
Proper watering techniques encourage the desired grass to develop deep roots, making it more competitive against shallow-rooted weeds. Infrequent, deep watering is preferred over frequent, shallow watering. Additionally, installing physical edging provides a defense against rhizomes and stolons that attempt to spread into garden beds or adjacent areas.
Barriers made of metal or rigid plastic should be installed deep enough to block underground runners. A barrier that extends at least five to eight inches into the soil is often recommended to effectively halt the spread of rhizomes. Regular maintenance, including overseeding thin areas, will help the turf remain dense and prevent the opportunistic invasion of any returning creeping grasses.