Clover, primarily species within the Trifolium genus, is valued for creating a resilient ground cover. As a legume, it forms a symbiotic relationship with soil bacteria, converting nitrogen from the air into a usable form for plant growth (nitrogen fixation). This ability positions clover as a powerful competitor against unwanted vegetation. Clover manages weeds not by chemically killing them, but by physically and biologically suppressing their growth.
The Mechanisms of Weed Suppression
Clover suppresses weeds through its dense growth habit, creating a thick canopy that blocks sunlight from reaching the soil surface. This physical shading prevents most weed seeds from germinating. Seedlings that emerge are quickly deprived of light energy, leading to stunted growth and eventual death.
The rapid spread of clover initiates fierce competition for resources within the soil. Clover aggressively absorbs available water and nutrients, leaving insufficient amounts for neighboring weed species to thrive. This resource depletion prevents weeds from developing the robust root systems and foliage needed to establish themselves.
Furthermore, clover’s ability to fix its own nitrogen enhances its competitive advantage. This fixed nitrogen benefits the clover, but not necessarily common lawn weeds, which rely on external sources. By securing its own nutrient supply, clover maintains a thick, healthy stand, outcompeting weeds struggling to find resources. Decomposing clover biomass may also release natural compounds that temporarily inhibit the germination of certain weed seeds (allelopathy).
Selecting and Establishing Clover for Weed Control
Successful weed suppression requires choosing the right clover variety. White Dutch Clover (Trifolium repens) is a traditional choice, known for its vigorous, creeping growth and tolerance of various soil conditions. Its larger leaves and taller habit effectively shade out weeds in large areas or pastures.
For a more manicured look, Microclover, a dwarf cultivar of white clover, is often preferred. It is bred to have smaller leaves and a lower growth profile, typically staying around four to six inches tall. Microclover varieties, such as ‘Pipolina’ or ‘Pirouette,’ establish a denser mat than traditional white clover, which is paramount for smothering weeds in existing lawns. Its compact nature also makes it more tolerant of frequent mowing and heavy foot traffic.
To establish a dense, weed-suppressing cover, soil preparation is important. Start with a soil test to ensure the pH is near neutral (ideally 6.5 to 7.0), which is optimal for clover growth. A high seeding rate (one to two pounds of Microclover seed per 1,000 square feet) is necessary to achieve density quickly. Planting is best timed for late summer or early fall, allowing root systems to establish before the spring weed flush.
During the initial establishment phase, consistent moisture is required to ensure the seeds germinate and the young plants can outcompete any existing weed seeds. It is also important to avoid applying nitrogen fertilizer, as this will inhibit the clover’s nitrogen-fixing mechanism and may encourage the growth of any remaining weeds. Giving the clover a strong, early start is the best way to leverage its competitive nature for long-term weed control.
Limitations and Ongoing Maintenance
While clover is a powerful suppressor, it is not a complete eradication method and has limitations, particularly concerning established perennial weeds. Clover is most effective against annual weeds that germinate from seed each year, which are easily blocked by the dense canopy. However, mature perennial weeds, such as dandelions or thistle, possess deep taproots and extensive underground energy reserves that allow them to push through the clover mat and survive the competition for light and nutrients.
Another limitation is the potential for seasonal gaps in coverage, which can allow opportunistic weeds to take hold. Clover can enter a state of dormancy during periods of extreme heat, prolonged drought, or hard winter freezes. When the clover thins out, even temporarily, the exposed soil provides a window for warm-weather or cool-weather annual weeds to germinate and establish themselves before the clover recovers.
Ongoing maintenance is required to ensure the clover remains an effective weed barrier. Occasional mowing is necessary to maintain a low, dense canopy, which encourages the plant to spread horizontally via its runners, or stolons. This process stimulates a tighter growth pattern, enhancing the smothering effect and preventing the clover from becoming too tall or leggy, which would allow light to penetrate to the soil level.