Turf grass in a flower bed is more than an aesthetic issue. Grass aggressively competes with ornamental plants for water and soil nutrients, often winning due to its dense, fibrous root system. This encroachment can stunt the growth and vibrancy of flowers, making safe removal a priority. Eliminating grass without harming desirable plants requires methods that are either precisely targeted or completely non-chemical.
Physical Removal Techniques
The safest approach for removing grass from an established flower bed is physical removal, which eliminates the need for chemicals. Hand-pulling is most effective for small infestations, but requires removing the entire root structure. For aggressive, spreading grasses like Bermuda grass or Quackgrass, the underground runners, known as rhizomes, must be completely extracted. These rhizomes penetrate the soil deeply and can re-sprout from small fragments left behind.
A technique known as smothering, or occultation, involves blocking sunlight to kill the grass over time. This method uses thick layers of cardboard or opaque plastic sheeting placed over the affected area. Smothering works best during the dormant season or before planting a new bed, requiring the area to be covered for several weeks to months to deplete the grass’s energy reserves. For existing beds, this method is limited to areas between established flowers.
Using Selective Herbicides Safely
For extensive grass invasion, a highly targeted chemical solution may be warranted. Non-selective herbicides, like those containing glyphosate, will kill any plant they contact and must be avoided near flowers. The safer option is a selective, grass-specific herbicide, typically containing sethoxydim or fluazifop-P-butyl. These chemicals kill grasses by interrupting lipid synthesis, a process that broadleaf ornamental plants lack, making them tolerant to the treatment.
These products should only be applied when the grass is actively growing and temperatures are between 65°F and 85°F for maximum effectiveness. Safe application requires extreme precision, often through spot-treating with a pump sprayer set to a coarse spray to prevent mist from drifting onto flowers. Using a physical shield, such as cardboard or an overturned bucket, to temporarily cover nearby ornamental plants is a necessary precaution. The systemic nature of the herbicide allows it to move from the leaves down to the grass roots, providing a thorough kill.
DIY Liquid Solutions
Many gardeners explore common household liquids as a non-chemical alternative to commercial herbicides. Horticultural vinegar, which contains a high concentration of acetic acid (typically 20% to 45%), acts as a contact killer. When sprayed directly onto grass, the high acidity rapidly draws moisture from the plant tissue, causing the tops to burn and wilt within hours. However, household vinegar (5% concentration) is generally too weak to affect established grass.
The main limitation of vinegar is that it rarely penetrates deep enough to kill the roots of perennial grasses, leading to regrowth. Furthermore, excessive application can temporarily lower the soil’s pH, negatively impacting non-acid-loving flowers. Boiling water is another popular method that instantly destroys the plant’s cell structure upon contact. While effective for small, shallow-rooted patches, the heat dissipates quickly, often failing to kill the deep rhizomes of tenacious grasses. Salt-based solutions should never be used in a flower bed, as the salt contaminates the soil, making it toxic for future plant growth by interfering with water and nutrient uptake.
Preventing Future Grass Invasion
Once the existing grass has been removed, long-term strategies are necessary to prevent re-infestation. Applying a thick layer of organic mulch is the most effective preventive step. A depth of three to four inches of material like wood chips or shredded bark suppresses grass seed germination by blocking sunlight. Mulch also conserves soil moisture and moderates soil temperature, creating a healthier environment for flowers.
Physical edging creates a permanent barrier against creeping grasses that spread via underground rhizomes. Installing metal, plastic, or stone edging to a depth of at least four to six inches is sufficient to block most turf grass runners. For highly aggressive grasses like Bermuda grass, a deeper barrier may be necessary as their rhizomes travel substantial distances. Landscape fabric underneath the mulch is not recommended in flower beds; while it initially suppresses weeds, it eventually hinders the exchange of air and water. As organic mulch decomposes on top, it creates a new layer where weed seeds can germinate.