Turfgrass encroaching into ornamental spaces is a persistent challenge, especially with aggressive, creeping varieties like Bermuda or Zoysia. These grasses use specialized stems—stolons (above ground) and rhizomes (below ground)—to rapidly spread into flower beds. Maintaining a clean boundary requires robust preventative measures and consistent, targeted maintenance to suppress invaders. This separation ensures that flowers and shrubs have the necessary space and resources to thrive without competition.
Installing Permanent Physical Barriers
Physical separation provides the most effective long-term defense against turfgrass runners and root systems. The barrier must extend deep into the soil to block subterranean rhizomes that allow grasses to spread aggressively. For most turf varieties, the barrier should be installed 4 to 6 inches below the soil line to intercept creeping root structures.
Materials like metal, rigid plastic edging, or concrete curbing are highly effective because they offer a continuous, vertical boundary. When installing these, a trench must be dug to the appropriate depth, ensuring the barrier is placed flush against the lawn side of the bed. The top edge of the barrier can be set slightly recessed or just above the soil line to accommodate lawn mowing.
Aggressive grasses like Bermuda are particularly problematic, often requiring a subsurface barrier because their roots can run deeper than 6 inches. An alternative to manufactured edging is creating a deep, empty trench that acts as a buffer zone that must be routinely maintained. This “natural” edge involves cutting a clean, vertical 3 to 4-inch deep wall into the soil and raking away debris, though it requires regular re-cutting to remain effective.
Manual and Cultural Suppression Techniques
Non-chemical methods focus on removing existing grass and suppressing new growth. When perennial grasses are established, complete manual removal of the root system is the most reliable way to prevent regrowth. This involves carefully digging out the entire plant and extracting all rhizomes and stolons, as even small fragments can re-root.
Mulching acts as an effective cultural suppression technique by blocking the sunlight required for grass seedlings to germinate and grow. A consistent, dense layer of organic mulch, such as shredded wood or bark chips, should be applied at a depth of 3 to 4 inches over the entire bed surface. Applying less than 3 inches allows light penetration and recovery, while deeper layers may limit oxygen to desirable plant roots.
For preparing a new bed or tackling large patches of established grass, solarization or smothering can kill existing vegetation before planting. This technique involves covering the area with opaque plastic or thick cardboard for several weeks to block all light and trap heat, which suffocates the grass. This method is useful for eliminating aggressive turfgrass types that have a dense network of underground stems.
Using Targeted Herbicides Safely
Chemical control offers a solution for grass that is difficult to access or resists manual removal, but it requires careful and targeted application to protect ornamental plants. Herbicides are categorized into non-selective types, which kill almost any plant they contact, and selective types, which target grasses while sparing broadleaf plants like flowers. Selective herbicides are particularly useful for killing grasses that have grown close to desirable plants.
Application must be highly specific to prevent herbicide drift onto flowers and shrubs, which can cause severe damage. Techniques like “painting” the herbicide directly onto grass leaves with a brush or using a hooded sprayer attachment ensure the chemical only contacts the target weed. Non-selective products containing glyphosate require caution, and nearby ornamental plants should be shielded with cardboard or plastic during application.
Always read the product label thoroughly to confirm the herbicide is safe for the specific ornamental plants and to understand the required safety gear. The label specifies the correct dilution rates and application timing, which is important for controlling annual and perennial grasses. Applying herbicides on calm, windless days prevents accidental chemical movement and safeguards the flower bed.