White clover (Trifolium repens) is a perennial plant often found spreading across lawns, recognizable by its characteristic three-leaflet leaves and small white flower heads. Many homeowners view clover as a persistent invader that disrupts the uniform appearance of turfgrass. The core concern is the perception that this low-growing plant actively smothers or “chokes out” the surrounding lawn. This article explores the relationship between clover and turfgrass to determine how this legume competes in a mixed sward.
Clover’s Competitive Strategy
Clover does not typically choke out healthy, vigorous grass through physical smothering, which is a common misconception. Unlike highly aggressive, vertical weeds that shade out turf, white clover maintains a prostrate, mat-like growth habit, spreading across the ground via creeping stems called stolons. These stolons root at the nodes, allowing the plant to rapidly colonize bare patches in the lawn.
Clover’s competitive advantage is not primarily about blocking sunlight, but rather about superior resource acquisition in certain conditions. Clover is tolerant of close mowing because its growing points are low to the ground, while repeated low cuts can weaken the grass. It competes with grass for water and light, but a dense, well-maintained turfgrass stand is generally competitive enough to prevent clover from becoming dominant.
The Role of Nitrogen Fixation
The real competitive edge for clover lies in nitrogen fixation. Clover is a legume, meaning it forms a symbiotic relationship with specialized soil bacteria. These bacteria inhabit nodules that form on the plant’s roots.
Within these root nodules, the bacteria convert atmospheric nitrogen gas into ammonium, a usable form of nitrogen for plant growth. This process allows the clover to fertilize itself continuously, thriving in soils that are naturally poor in nitrogen where turfgrass struggles. The nitrogen fixed by the clover is not only used by the legume itself, but also becomes available to the surrounding grass as clover roots and leaves naturally decay. This shared nitrogen resource allows the grass to grow better near the clover, leading to the appearance of clover “dominance” in areas where the grass was already weak due to nutrient deficiency.
Managing the Balance Between Grass and Clover
Homeowners can manipulate the grass-clover balance by adjusting maintenance practices, which directly impacts the competitive environment. Applying synthetic nitrogen fertilizer is the most effective way to favor grass dominance. Additional nitrogen negates clover’s primary advantage, allowing the grass to become denser and outcompete the clover for light and space.
The height of the mower also plays a role in light competition. Mowing at a higher setting (three inches or more) favors the taller turfgrass by increasing its leaf surface area for photosynthesis. Conversely, consistently low mowing provides more light to the prostrate clover, encouraging its spread. Clover is also more tolerant of drought conditions than many common turfgrasses due to a slightly deeper root system. Watering less frequently, but more deeply, encourages grass roots to grow deeper, improving competitiveness against the clover’s shallower stolons.