Dollar weed (Hydrocotyle spp.), also known as pennywort, is a perennial weed that can rapidly colonize a lawn. This weed is easily identified by its bright green, fleshy leaves that are perfectly round, resembling miniature silver dollars with the stem attached in the center of the leaf’s underside. It has a low-growing habit and spreads aggressively through seeds, tubers, and an extensive network of underground stems called rhizomes. Dollar weed thrives in conditions of excessive moisture and weak turf, making its control difficult until the underlying environmental factors are addressed.
Addressing the Root Cause Through Cultural Control
The presence of dollar weed is a clear sign that the lawn environment is too wet, signaling an underlying issue that must be corrected for long-term control. Dollar weed is a water-loving plant that flourishes where turfgrass struggles, especially in saturated soil conditions. Correcting irrigation practices is the most effective first step in controlling this weed.
Shifting to a deep, infrequent watering schedule is necessary to discourage dollar weed. Instead of light, daily sprinkling, the lawn should receive approximately one to one and a half inches of water per week, applied in a single session. Allowing the soil surface to dry out between watering sessions creates an environment less favorable for the weed’s shallow root system while encouraging deeper root growth in the desirable turfgrass.
Areas with persistent water pooling or slow drainage must be identified and corrected. Compacted soil can be improved through aeration, which reduces surface water retention and allows for better water penetration. In severely waterlogged areas, improving the grade or adding topdressing may be necessary to promote effective water runoff away from the lawn.
Maintaining the proper mowing height for your specific turfgrass species is another cultural control method. Mowing too short stresses the grass, thinning the turf canopy and allowing more sunlight to reach the soil, which favors dollar weed germination. A taller, denser lawn shades the soil and physically crowds out emerging weeds, helping the turf to naturally outcompete the perennial weed.
A balanced fertilization program supports a thick, resilient lawn that resists weed invasion. Healthy turfgrass is the best defense against all weeds. Regular soil testing can determine the specific nutrient needs, ensuring the lawn receives the proper balance to maximize density and vigor.
Manual Removal and Non-Chemical Solutions
For small, isolated patches, physically removing the dollar weed can offer immediate relief, especially for homeowners avoiding synthetic chemicals. When hand-pulling, it is critical to remove the entire plant, including the extensive root system and any attached underground rhizomes. Leaving even small fragments of the rhizome or tuber behind will inevitably lead to rapid regrowth.
Several non-commercial spot treatments are available, though they require careful application and have limited effectiveness on large infestations. Pouring boiling water directly onto the weed will instantly kill the foliage and root structure it contacts. However, this method is non-selective and will destroy any desirable turfgrass or ornamental plants the water touches.
A horticultural vinegar solution, which has a higher acetic acid concentration than common household vinegar, can also be used as a contact herbicide. Like boiling water, vinegar is non-selective and will burn any plant tissue it is sprayed upon, making it suitable only for highly targeted spot treatments. These non-chemical options are best reserved for small areas or for homeowners who can tolerate minor damage to the surrounding lawn.
Targeted Herbicide Application for Eradication
When cultural controls and manual efforts are not enough to manage a widespread infestation, a targeted chemical approach becomes necessary. The most effective chemical control relies on selective, post-emergent herbicides. A selective herbicide is formulated to target broadleaf weeds, such as dollar weed, while leaving the surrounding turfgrass unharmed.
Post-emergent products are applied directly to the existing, actively growing weeds. The most common and effective active ingredients found in these products include 2,4-D, dicamba, and MCPP (mecoprop). These are often combined into a “three-way” broadleaf herbicide formulation to increase the spectrum and efficacy of the treatment. For certain warm-season grasses like St. Augustine and centipedegrass, products containing atrazine may be recommended, as they can act as both a pre- and post-emergent control.
Timing the application is a major factor in achieving success, as herbicides are most effective when the dollar weed is actively growing. The ideal time is typically in the late spring or early summer when temperatures are consistently in the 60 to 85-degree Fahrenheit range. Following the product label precisely is mandatory, including using the correct mixing ratios and wearing appropriate personal protective equipment.
Because dollar weed spreads aggressively through its robust underground rhizomes, a single herbicide application is rarely sufficient for complete eradication. Multiple treatments are almost always required to exhaust the weed’s ability to regenerate from these underground structures. A second application should generally be made two to four weeks after the initial treatment, or as specifically directed by the manufacturer’s instructions.