Clover is a persistent, low-growing broadleaf weed that can quickly invade a healthy lawn. As a legume, clover fixes its own nitrogen, giving it a competitive edge over turfgrasses, especially in nutrient-deprived soil. St. Augustine grass is a common warm-season turf in Southern regions, but it is sensitive to many common broadleaf herbicides. Effectively removing clover requires a careful approach that protects the St. Augustine turf while eliminating the weed. This process involves cultural practices, non-chemical removal, and selective herbicide use.
Preventing Clover Through Lawn Maintenance
Maintaining a dense, healthy St. Augustine lawn is the most effective long-term defense against clover invasion. Clover thrives in thin, weak turf and areas with low soil fertility.
Proper mowing height is a powerful cultural control. St. Augustine grass should be cut at a height of 3 to 4 inches. This tall canopy shades the soil, blocking the sunlight clover seeds need to germinate and suppressing the growth of existing clover.
The turf benefits from deep, infrequent watering rather than light, daily irrigation. Deep watering encourages a strong, deep root system, helping the grass outcompete shallow-rooted clover. Applying a slow-release nitrogen fertilizer also suppresses clover, as the weed often indicates low soil nitrogen.
Non-Chemical Removal Methods
For small, isolated patches of clover, physical removal avoids chemical application. Hand-pulling is effective, but the entire root system must be extracted to prevent regrowth. Clover spreads via stolons (above-ground stems), so following these runners back to their source is necessary for complete removal.
Horticultural vinegar solutions can be applied directly to the clover as a non-toxic spot treatment. These solutions have a high acetic acid content that will desiccate and kill the plant tissue. Caution is necessary, as the high acidity will also damage any St. Augustine grass it contacts. Apply the vinegar only to the clover and test a small area first to gauge its effect.
Choosing the Right Herbicide for St. Augustine
St. Augustine grass is highly sensitive to many broadleaf herbicides, including those containing 2,4-D, MCPP, or Dicamba. Applying common “weed and feed” products without checking the label can result in yellowing, stunted growth, or turf dieback.
The most widely recommended active ingredient for clover control in St. Augustine grass is Atrazine. Atrazine works as both a pre-emergent, preventing new seeds from sprouting, and a post-emergent, controlling existing clover and other broadleaf weeds. It is safe for St. Augustine varieties when applied according to the label instructions.
Another suitable post-emergent option is an herbicide specifically formulated for warm-season turfgrasses.
Application timing is crucial; herbicides should be applied when temperatures are below 90°F to minimize stress and potential damage to the St. Augustine grass. Always spot-treat a small area first to confirm the turf’s tolerance before widespread application.