Japanese clover, scientifically known as Kummerowia striata and sometimes called common lespedeza, is a low-growing summer annual weed that quickly dominates lawns. This plant aggressively competes with turfgrass, forming dense mats that thrive where grass struggles. Managing its spread requires a targeted, multi-faceted approach. Eliminating Japanese clover involves accurately identifying the plant, understanding its life cycle, and implementing both non-chemical and chemical control strategies.
Identifying Japanese Clover and Its Growth Cycle
Identifying Japanese clover is the first step toward effective control. The plant has a prostrate, mat-forming growth habit, with wiry stems that branch close to the soil surface. Its leaves are trifoliate, arranged in sets of three oblong, dark green leaflets with parallel veins. As the season progresses, the stems become woody, making mature plants difficult to pull and resistant to some treatments.
Japanese clover is a summer annual, completing its life cycle within one growing season. Seeds germinate in the late spring or early summer when soil temperatures are consistently high. The plant grows vigorously during the hot months and produces a large number of seeds in the fall before dying with the first hard frost. This life cycle dictates that control measures must target either the germinating seeds in spring or the actively growing plants in summer.
Non-Chemical Removal Techniques
For small, isolated patches of Japanese clover, manual removal is a practical and safe option. Hand-pulling is most effective when the plants are young and the soil is moist, allowing the entire root system to be extracted before the stems become woody. Ensuring the root is completely removed prevents any regrowth and manages initial infestations.
Adjusting the mowing height is a powerful cultural practice to suppress clover growth. Japanese clover thrives when turfgrass is cut short, but raising the mower blade to three or four inches gives the grass a competitive advantage. Taller turf shades the soil surface, inhibiting clover seed germination by blocking sunlight. This practice encourages a denser lawn that physically crowds out the low-growing weed.
The weed’s presence often signals underlying issues with soil health. Japanese clover frequently colonizes areas with poor, dry, or compacted soil that is low in nitrogen. Aerating the lawn helps alleviate compaction, improving the movement of air, water, and nutrients to the grass roots. A soil test can reveal if the pH is too acidic, which favors clover over turfgrass. If the test indicates low pH, applying lime can raise the pH to a level conducive to healthy grass growth.
Selecting and Applying Herbicides
Chemical control is often necessary for large or widespread infestations, and timing the application is crucial. Herbicide options are categorized into pre-emergent and post-emergent treatments, each targeting a different stage of the weed’s life.
Pre-emergent herbicides form a chemical barrier that stops seeds from germinating. To be effective, these products must be applied in early spring, before the soil temperature consistently reaches the low-to-mid 50s degrees Fahrenheit. Active ingredients such as atrazine or simazine are sometimes used for control, though their use may be restricted in residential areas. Always read the product label to ensure the herbicide is safe for your specific turfgrass type.
Post-emergent herbicides are applied after the clover has emerged and is actively growing, typically during the summer months. The most effective products for broadleaf weeds like Japanese clover are selective herbicides containing a combination of active ingredients, often called “three-way” mixes. Look for formulations that include 2,4-D, dicamba, MCPP (mecoprop), or triclopyr. Dicamba and triclopyr are generally the most effective components for controlling this weed.
When applying post-emergent herbicides, target the actively growing plants and ensure temperatures remain below 85°F to 90°F to prevent turfgrass damage. Avoid spraying dicamba products near the root zones of desirable trees and shrubs, as they can absorb the chemical. Applying a second treatment two to four weeks after the initial application may be necessary to fully eradicate mature stands.
Maintaining a Clover-Free Lawn
Long-term prevention relies on cultivating a dense, healthy lawn that naturally resists weed invasion. Since Japanese clover is a legume and fixes its own nitrogen, regular fertilization with a nitrogen-rich product is a powerful strategy to favor turfgrass growth.
Overseeding the lawn in the fall with desirable turf varieties helps fill in thin or bare spots where clover seeds might germinate the following spring. A thick stand of grass leaves no open ground for weed establishment, acting as a natural defense. This practice, combined with proper nutrient management, ensures the turf is robust enough to compete with stray clover plants.
A deep, infrequent watering schedule is preferred over frequent, shallow watering. Deep watering encourages the grass to develop strong, extensive root systems, making the turf more resilient to stress and less hospitable to surface-germinating weeds. Periodic soil testing should be part of the annual maintenance plan to ensure pH and nutrient levels remain optimal for your specific turfgrass.