St. Augustine grass is known for its lush, carpet-like appearance but is notorious for its aggressive growth habit. It uses thick, above-ground runners, or stolons, to spread rapidly. This tenacious nature makes complete removal difficult, especially when replacing it with a different landscape. Simply digging it up often leaves viable stolon segments behind, which quickly regenerate. Complete eradication requires a targeted, systematic approach that addresses both the above-ground foliage and the extensive runner system to prevent rapid regrowth.
Preparing the Area for Removal
Proper preparation maximizes the effectiveness of any eradication technique. Begin by mowing the St. Augustine grass as low as possible. This physically removes a significant portion of the leaf surface and concentrates the plant’s energy reserves into the remaining runners and crown, making it more vulnerable to treatment. Lightly water the area, as moist soil conducts heat efficiently for solarization and helps the grass absorb systemic herbicides. Finally, clearly define the border of the area, using a spade to cut a trench or placing a physical barrier to protect adjacent landscaping from accidental exposure or chemical drift.
Non-Chemical Eradication Techniques
For homeowners seeking an organic approach, two effective non-chemical methods are soil solarization and sheet mulching. Soil solarization uses the sun’s energy to generate lethal temperatures within the topsoil, killing the grass and weed seeds. To apply this method, thoroughly water the area, then cover it with clear, UV-resistant plastic sheeting, typically 2 to 6 millimeters thick.
The edges of the plastic must be completely sealed by burying them in a trench or weighing them down with soil. This tight seal traps heat and moisture, creating a greenhouse effect that raises soil temperatures to 110°F to 140°F in the top few inches. To ensure the stolons are fully killed, this process requires a minimum of four to six weeks during the hottest part of the year (June through August).
Sheet mulching, also known as lasagna layering, works by depriving the grass of sunlight and airflow, causing it to decompose in place. Start by laying a thick layer of brown corrugated cardboard directly over the low-cut grass, removing all plastic tape and staples. Overlap the edges of the cardboard by at least six to eight inches to prevent runners from finding light.
Once the cardboard is laid down and dampened, cover it with four to six inches of organic material, such as wood chips or compost. The absence of light halts photosynthesis, and the organic material accelerates decomposition. This method requires a longer wait time, typically six to eight weeks, to fully kill the grass and allow the cardboard to begin breaking down.
Using Herbicides for Complete Removal
When quick and complete eradication is necessary, a non-selective systemic herbicide is the most reliable option. Glyphosate is widely used because it is absorbed through the foliage and translocates throughout the entire plant, including the aggressive stolon system. Unlike some other chemicals, glyphosate is neutralized on contact with the soil and does not leave a residual effect that prevents future planting.
Application must occur when the grass is actively growing and healthy to allow for maximum absorption. The optimal temperature range for glyphosate performance is between 60°F and 75°F; avoid application during extremely cold or hot, drought-stressed conditions. Apply the product on a calm day to prevent spray drift, protecting desirable plants with a physical barrier like a cardboard shield.
Mix the product according to the label’s instructions for the appropriate concentration, typically around 1.5 ounces of a 41% concentrate per gallon of water for a blanket spray. Apply the mixture evenly to all leaf surfaces, ensuring a thorough coating without runoff. Because St. Augustine grass is resilient, a single application may not be sufficient, and a follow-up spray may be necessary ten to fourteen days later to eliminate surviving runners or new growth.
The grass takes time to die, with visible results often appearing only after seven to ten days. Full desiccation typically requires up to two weeks.
Post-Eradication Soil Management and Prevention
Once the St. Augustine grass is visibly dead, the final phase involves clearing the area and preparing the soil for its next use. Rake up and remove dead plant material, or compost it separately if chemicals were used. If a non-selective herbicide was applied, a waiting period of two to three weeks is recommended before planting new turf or garden materials.
If the area was treated with solarization or sheet mulching, the dead organic material can be tilled directly into the soil to improve organic matter content. For new planting, amend the soil with compost or other organic material to replenish nutrients and improve structure. This is important following solarization, which can temporarily deplete some soil biology.
A dedicated period of monitoring is necessary to prevent regrowth from overlooked runners or dormant seeds. Lightly watering the area for a couple of weeks encourages the germination of remaining weed seeds, which can then be easily removed by hand or spot-sprayed.