Unwanted grass within an established flower bed poses a unique challenge. Turfgrass competes aggressively with ornamental plants for water, nutrients, and sunlight. Removing this growth without disturbing the delicate roots of desirable flowers requires a calculated approach based on identifying the grass type and selecting the appropriate strategy.
Physical Removal Techniques
Manual removal is the most immediate and safest method for extracting grass. Removing the entire root structure is the primary focus, as leaving small fragments of underground stems leads to rapid regrowth. Tools like a weeding fork, trowel, or a specialized V-shaped handheld weeder are ideal for isolating and lifting individual clumps without disturbing surrounding soil.
This careful approach is important when dealing with aggressive, rhizomatous grasses such as Bermuda grass or Quackgrass. These grasses spread via rhizomes, which can sprout a new plant from even a one-inch piece. While most rhizomes are found in the top six inches of soil, Bermuda grass roots can extend much deeper, requiring a thorough, shovel-depth excavation for complete removal.
When grass is tightly woven around the base of a perennial flower, use a hori-hori knife or a small hand cultivator to carefully loosen the surrounding soil. Once loose, the grass clump can be gently teased out, minimizing damage to the flower’s fine root hairs. Inspect excavated soil for rhizome pieces before returning it to the bed, and discard removed grass rather than composting it to prevent reintroduction.
Non-Chemical Smothering and Suppression
For larger, dense patches of grass where manual weeding is impractical or too disruptive, non-chemical suppression offers a long-term solution. This technique works by depriving the grass of the sunlight needed for photosynthesis. Sheet mulching is the most effective way to achieve this.
The process involves laying down a light-blocking barrier, typically consisting of overlapping layers of corrugated cardboard or ten to fifteen sheets of newspaper. The material must be thoroughly wetted down to initiate decomposition and ensure it remains securely in place. The barrier should overlap by at least six inches at the seams to prevent grass from finding a path to light.
Apply a thick layer of organic mulch (wood chips or shredded bark) over the barrier. For effective suppression, this top layer should be maintained at a depth of four to six inches. This combination blocks light, causing the grass underneath to die and decompose over several months. If the flower bed is already planted, keep the mulch and barrier material several inches away from the stems and crowns of desirable plants to prevent rot.
Strategic Use of Herbicides
Chemical control provides a targeted option for grass removal, but it requires precision to protect existing ornamental plants. Herbicides are categorized as either non-selective (killing nearly all plant tissue) or selective (targeting specific plant types while sparing others). Selective, grass-specific herbicides are often preferred in a flower bed, as they eradicate grass while leaving broadleaf flowers unharmed.
When using any chemical application, the label instructions must be followed exactly, and appropriate personal protective equipment should be worn. Non-selective options, such as glyphosate, are highly effective but must be applied with caution to avoid drift or runoff onto desirable plants. Spot-treating individual grass clumps using a dedicated foam brush or sponge applicator to paint the chemical directly onto the foliage is one technique.
Alternatively, a physical shield can be placed around the grass before spraying to prevent overspray from damaging flowers and shrubs. An empty coffee can or cardboard can isolate the target grass clump during application. Apply herbicides on a calm, windless day, and treat the grass when it is actively growing to ensure the chemical is rapidly absorbed and translocated down to the root system for a thorough kill.
Preventing Future Grass Invasion
Once the existing grass is removed, implementing preventative measures is necessary. Grass invades through two primary mechanisms: sending underground runners from the adjacent lawn and by seed dispersal. Installing a physical barrier along the perimeter is the most effective way to block the aggressive horizontal spread of grass rhizomes and stolons.
The barrier material (metal, durable plastic, or paving stones) must be installed deep enough to intercept the underground runners. A minimum depth of four to six inches into the soil is necessary to create an effective subterranean wall. The top edge of the barrier should also extend an inch or two above the soil line to prevent above-ground runners and mulch from spilling out.
Beyond the hard barrier, maintaining a layer of organic mulch acts as a secondary defense against both grass seeds and shallow runners. A layer of shredded wood or bark mulch three to four inches thick will suppress the germination of wind-blown grass seeds. This depth also creates a dry zone that discourages shallow surface runners from rooting. Routine maintenance, such as yearly replenishment of the mulch layer and immediate removal of any grass that manages to sprout, secures the flower bed’s long-term health.