Clover (most commonly Trifolium repens, or white clover) is a perennial legume often viewed as an invasive weed in traditional turfgrass lawns. Homeowners frequently debate whether it helps or harms their grass. The perception that clover damages turf is largely due to its appearance and its ability to spread rapidly. The relationship between clover and grass is a complex interaction involving competition for resources and a unique symbiotic benefit. This interaction determines if clover dominates the lawn or integrates into a thriving green space.
Clover’s Competitive Strategy
Clover does not possess any toxic or chemical mechanism to directly kill turfgrass. Instead, its impact is based on a highly effective competitive strategy that allows it to outcompete and suppress weaker grass. The plant’s aggressive, low-growing architecture, known as a stoloniferous growth habit, is central to its dominance. These horizontal stems, or runners, creep along the soil surface, rooting at the nodes to form dense patches that expand rapidly.
When turfgrass is thin, stressed, or poorly maintained, clover’s dense mat-like growth smothers the grass beneath it. This growth blocks sunlight required for photosynthesis, causing the underlying turf to weaken and die. Clover also exhibits superior drought tolerance compared to many common turfgrass varieties. When water is scarce, turfgrass struggles, but clover thrives, quickly taking over exposed soil patches.
Clover’s success often signals an underlying issue in the lawn, particularly a lack of nitrogen. Turfgrass requires high amounts of nitrogen to maintain density and color, so a shortage creates a weak sward that clover exploits. By flourishing in conditions that stress the grass, clover appears to cause the decline, but it is actually a symptom of the grass’s inability to compete.
The Unexpected Benefit of Nitrogen Fixation
The perceived harm clover causes is balanced by a significant benefit to companion grasses through nitrogen fixation. As a legume, clover forms a symbiotic relationship with specialized soil-dwelling Rhizobium bacteria. These bacteria colonize structures on the clover roots called root nodules.
The bacteria convert atmospheric nitrogen gas, which is unusable by plants, into a stable organic compound like ammonium. This nitrogen fixation process acts as a natural, slow-release fertilizer for the clover.
When clover leaves or roots decompose, these nitrogen compounds are released into the soil for nearby grass to utilize. This improves the turfgrass nutrient status, leading to darker green color and healthier growth. A sward containing clover can maintain high quality with significantly less synthetic nitrogen fertilizer application.
Methods for Clover Management
Management of clover depends entirely on the homeowner’s goal: complete removal or beneficial integration. To eliminate clover, cultural practices that favor grass growth are the most effective long-term solution. Mowing the lawn at a higher height, ideally three to four inches, helps grass blades shade the low-growing clover, hindering its access to sunlight.
Watering deeply and infrequently encourages the grass to develop deep, robust roots, improving its drought resistance against the shallow-rooted clover. Since clover thrives in nitrogen-poor soil, applying a nitrogen-rich fertilizer strengthens the grass and weakens the clover’s competitive advantage. For immediate removal, selective broadleaf herbicides containing active ingredients like 2,4-D or triclopyr are effective, as they target the clover without harming the grass.
Conversely, homeowners can encourage clover’s presence by reducing or eliminating synthetic nitrogen fertilizer applications, which pushes the clover to fix more nitrogen naturally. Introducing microclover, a smaller variety of white clover, provides the nitrogen-fixing benefits while maintaining a more uniform, lawn-like appearance. Allowing the clover to flower also supports local pollinator populations, enhancing the ecological value of the lawn.