Japanese Clover (Kummerowia striata or Lespedeza striata) is a common, aggressive lawn weed that can rapidly overtake a yard. This summer annual broadleaf plant is characterized by its prostrate, mat-forming growth habit and trifoliate leaves, which hug the ground and choke out desirable turfgrass. It thrives in poor, thin, and compacted soils, often becoming most noticeable in mid-summer. Eliminating this weed requires a multi-pronged approach addressing both the existing plants and the underlying lawn conditions.
Non-Chemical Removal Strategies
A dense, healthy lawn provides the best defense against Japanese Clover, as the weed struggles to establish itself under shade. Raising the mowing deck to a height of 3 to 4 inches allows the turfgrass to grow taller, effectively blocking the sunlight that clover seedlings need to germinate and develop. This cultural control method leverages the grass’s natural ability to outcompete weeds.
Adjusting irrigation practices also favors turfgrass over the shallow-rooted clover. Watering deeply and infrequently encourages the grass to develop deep, robust root systems, making it more resilient to drought and better able to compete. Conversely, light, frequent watering keeps the topsoil consistently moist, which is ideal for Japanese Clover germination and growth.
For small, newly established patches, physical removal through hand-pulling is a viable option. Japanese Clover develops a semi-woody taproot, so it is easiest to remove when the soil is moist and the plants are young. If the infestation is contained to a small area, covering the patch with clear plastic sheeting for several weeks, a process known as solarization, can use the sun’s heat to kill the plants and sterilize the top layer of the soil.
Chemical Control: Pre- and Post-Emergent Treatments
Chemical control is often necessary for widespread or heavily established infestations, utilizing selective herbicides that target broadleaf weeds without harming the turfgrass. These treatments are categorized into two main types: pre-emergent and post-emergent. Pre-emergent herbicides, such as those containing dithiopyr, are applied before the weed seeds germinate to form a chemical barrier in the soil.
The optimal timing for pre-emergent application is in the late winter or early spring, before soil temperatures consistently reach 55 to 60 degrees Fahrenheit, which signals the clover seeds to sprout. Post-emergent herbicides are used to kill existing, actively growing plants, with the best results seen when the clover is young and has not yet developed its woody taproot or set seed. These are typically applied in the late spring or early summer once the weed is clearly visible.
Effective post-emergent products for Japanese Clover often contain a combination of active ingredients like 2,4-D, dicamba, and triclopyr. This “three-way” mix works by disrupting the plant’s growth hormones, leading to its demise. For the herbicide to be absorbed efficiently, apply it when the weed foliage is dry, temperatures are moderate (ideally below 85 degrees Fahrenheit), and no rain is expected for at least 24 hours.
When applying any herbicide, follow all label instructions precisely, especially concerning personal protective equipment and application rates. Avoid spraying herbicides containing ingredients like dicamba near the root zones of desirable trees and shrubs, as they can absorb the chemical and suffer damage. Multiple applications, spaced according to the product label, may be necessary to gain full control over a dense patch of Japanese Clover.
Post-Eradication Lawn Management
Once the Japanese Clover has been successfully killed, the focus shifts to repairing the turf and altering the environmental conditions that promoted the weed’s growth. The first step involves removing the dead plant material and conducting a soil test to determine the existing pH and nutrient levels. Japanese Clover thrives in acidic soil with a pH below 6.0, so applying lime to raise the soil pH into the optimal range for turfgrass will make the area less hospitable to the weed.
Soil compaction, which also favors the clover, must be addressed through core aeration. This process removes small plugs of soil to improve air, water, and nutrient penetration. Aeration should be immediately followed by overseeding the bare patches with a desirable grass species to quickly establish a dense turf canopy. This is most effective in the fall for cool-season grasses or late spring for warm-season varieties, providing the new seedlings with ideal growing conditions.
A strategic fertilization program is then implemented to maintain a vigorous, thick lawn that can outcompete any new weed seedlings. Because Japanese Clover is a legume that can fix its own nitrogen, it flourishes in nitrogen-poor soil. Consistent application of a nitrogen-rich fertilizer is beneficial for the turf. By combining soil amendment, aeration, overseeding, and proper feeding, the lawn is strengthened, creating a natural barrier against the re-establishment of Japanese Clover.