The appearance of clover (Trifolium repens) in an otherwise uniform lawn is a common source of frustration for homeowners seeking a manicured turf appearance. Clover is a broadleaf weed, distinguishing it from the desired grass species in a lawn. Unlike many invasive plants, clover often flourishes in conditions that cause turfgrass to struggle. Successfully controlling this plant requires understanding its unique biology and employing targeted chemical or cultural strategies, as general-purpose weed killers often fail to eliminate clover effectively.
Understanding Clover’s Tolerance to Common Herbicides
Many common weed control products are ineffective against established clover due to several biological adaptations. One significant feature is the waxy leaf cuticle, a protective layer that causes liquid herbicides to bead up and run off, limiting the amount absorbed into the plant tissue. Clover also spreads aggressively via stolons, which are creeping stems that run along the soil surface and root down at the nodes. A single herbicide application may kill the visible leaf structure but fail to eliminate the entire network of stolons, allowing the plant to quickly re-establish itself.
Clover also possesses a unique advantage over turfgrass because it is a legume that can fix atmospheric nitrogen into the soil. This process allows it to thrive in nitrogen-poor soil where turfgrass growth is stunted. When a lawn is under-fertilized, clover has a competitive edge, making it less susceptible to the nutrient-deprivation effects that sometimes accompany general weed treatments. This ability to produce its own nitrogen allows it to maintain vigor even when stressed.
Identifying Effective Chemical Solutions
To successfully remove clover without harming the surrounding turf, it is necessary to use selective broadleaf herbicides. These products target the metabolic pathways found in broadleaf plants, like clover, while leaving narrow-leaf grasses unharmed. Non-selective options, such as glyphosate, will kill clover but also destroy the lawn, making them suitable only for spot treatments or preparing a complete lawn renovation. The most effective clover control products are typically combinations of multiple active ingredients, often referred to as “three-way” or “four-way” herbicides.
Primary Active Ingredients
These combination products utilize chemicals that disrupt the plant’s growth hormones, causing uncontrolled and lethal growth. The primary active ingredients to look for are 2,4-D, MCPP, and Dicamba.
##### 2,4-D (2,4-Dichlorophenoxyacetic acid)
This is an auxin-type herbicide that causes broadleaf weeds to grow themselves to death. It is often not strong enough on its own to completely eradicate clover.
##### MCPP (Mecoprop)
MCPP provides enhanced control against clovers and other hard-to-kill creeping weeds.
##### Dicamba
Dicamba is included to improve effectiveness against a wider range of broadleaf plants, including clover, by mimicking plant growth hormones.
Another highly effective chemical against established clover is Triclopyr, which is particularly potent against various broadleaf weeds and is often included in four-way mixes. The combination of these chemicals works synergistically to overcome clover’s natural defenses, ensuring the herbicide is absorbed and translocated throughout the stolons and root system. Because of the waxy cuticle, it is recommended to mix a non-ionic surfactant (wetting agent) with the spray solution. This helps the herbicide spread and adhere to the clover leaves for maximum absorption. Always verify that the chosen herbicide product is safe for your specific type of turfgrass to prevent accidental damage.
Optimizing Application Timing and Technique
The timing of herbicide application significantly influences the effectiveness of clover control. The most opportune time to treat clover with a post-emergent selective herbicide is in the early fall when the plant is actively storing nutrients in its roots to prepare for winter. Applying the chemical during this period means the plant will naturally draw the herbicide down into the entire root structure, resulting in a more complete kill. Spring application is also effective when the clover is actively growing, though a follow-up treatment may be necessary.
Avoid applying herbicides during periods of extreme heat, typically when temperatures exceed 80 to 90 degrees Fahrenheit, as this can stress the turfgrass and increase the risk of injury. For optimal absorption, the clover should not be mowed for at least two days before treatment, allowing the foliage to maximize the surface area for contact. Conversely, the lawn should not be mowed for a few days after application to give the plant sufficient time to absorb and translocate the chemical.
Precise application technique is just as important as the timing of the treatment. Ensure the herbicide is mixed and applied exactly according to the manufacturer’s label instructions for the specific type of sprayer being used. Due to the clover’s vigorous creeping habit, a single application is often insufficient to achieve complete eradication. A second treatment, typically applied 10 to 14 days after the initial application, is usually required to eliminate any plants that were missed or that have resprouted.
Non-Chemical and Cultural Control Methods
For those preferring to avoid chemical herbicides, or as a preventative measure, cultural practices can effectively suppress clover growth. One simple method is adjusting the mowing height to at least three inches, which encourages taller, denser turf. The taller grass blades will shade the soil surface, inhibiting the light-dependent growth of low-lying clover and reducing its ability to spread. This gives the desirable turfgrass a competitive advantage.
Proper fertilization is another powerful tool because clover thrives in soil with low nitrogen content, a condition that stunts grass growth. Applying a nitrogen-rich, slow-release fertilizer in the spring and fall promotes a dense, healthy lawn that naturally outcompetes the clover for space and resources. For small patches, manual removal is a viable option. It is easiest to pull the clover when the soil is moist to ensure the entire root system is extracted. Alternatively, organic pre-emergent products, such as corn gluten meal, can be applied to prevent clover seeds from germinating, though they will not affect already established plants.