Clover, typically white clover (Trifolium repens), is a broadleaf weed whose structure is fundamentally different from grass. Successfully removing clover without harming the lawn relies on selective control methods that exploit these biological differences. This selective approach involves the precise application of chemical treatments and cultural practices that favor turfgrass growth.
The Structural Difference Between Clover and Grass
The ability to selectively eliminate clover without damaging grass is rooted in the botanical difference between dicots and monocots. Clover is a dicotyledonous plant (dicot), characterized by two seed leaves, net-like leaf veins, and an exposed growing point. Grasses are monocotyledonous plants (monocots), featuring a single seed leaf, parallel leaf veins, and a protected growing point near the soil crown.
Selective broadleaf herbicides target the growth mechanisms unique to dicots. These chemicals mimic the natural plant hormone auxin, which regulates cell growth. When dicots absorb these synthetic auxins, the chemical overload causes uncontrollable growth, leading to distorted stems, leaf curling, and the collapse of the vascular system. Monocot grasses possess a different metabolic pathway that allows them to process and detoxify these hormone mimics before fatal damage occurs.
Active Ingredients for Selective Herbicide Application
Selective post-emergent herbicides are systemic, meaning they are absorbed through the leaves and translocated throughout the entire plant, including the roots. Effective products combine multiple active ingredients to increase the spectrum of weeds controlled and target clover’s resilience. These mixtures are often called “three-way” herbicides and typically include 2,4-D, MCPP, and Dicamba.
The active ingredient 2,4-D is a synthetic auxin that causes rapid, abnormal growth, leading to the weed’s demise. MCPP (mecoprop) is a related phenoxy herbicide that provides enhanced control of creeping weeds like clover. Both compounds disrupt the plant’s hormonal balance, resulting in the twisting and distortion of stems and leaves shortly after application.
Dicamba is a benzoic acid herbicide that also acts as a synthetic auxin, inducing abnormal cell division and growth. This combination of hormone mimics ensures the weed is targeted with multiple modes of action. For tough or mature clover, the active ingredient Triclopyr is often recommended, as it is effective on creeping perennial broadleaf weeds. Liquid herbicides should be applied when temperatures are moderate (65 to 85 degrees Fahrenheit) and when the clover is actively growing.
Long-Term Suppression Through Cultural Practices
While herbicides offer immediate control, long-term clover suppression is achieved by adjusting turf maintenance to favor grass growth. Clover often establishes itself in lawns where the turf is thin or stressed, or in soil that is compacted or low in nitrogen. Improving the lawn’s health naturally crowds out the clover and prevents re-establishment.
Adjusting the mowing height is an effective cultural practice. Taller grass blades, typically between three and four inches, create shade at the soil level. This shading inhibits the germination and growth of low-growing weeds like clover. A taller turf canopy also cools the soil, reducing stress on the grass.
Clover is a legume, meaning it fixes atmospheric nitrogen into the soil, giving it an advantage in nutrient-poor conditions. Applying nitrogen-rich fertilizer supports the turfgrass, which cannot fix its own nitrogen, allowing it to grow thicker and denser. A well-fertilized, dense lawn naturally suppresses clover by denying it space and light.
Practices like aeration and dethatching reduce soil compaction and improve the movement of water and nutrients to the grass roots. Healthy soil minimizes stress on the turf, allowing it to grow strong enough to resist weed invasion. Consistent maintenance of the turf environment reduces the need for repeated chemical intervention.