Dollar weed (Hydrocotyle spp.), also known as pennywort, is a warm-season perennial weed that challenges lawns and gardens. This aggressive plant is identified by its bright green, circular leaves with a stem attached at the center, resembling miniature lily pads. Dollar weed spreads rapidly through seeds, underground rhizomes, and tubers, quickly forming dense mats in turfgrass. Eliminating this nuisance requires a comprehensive strategy that addresses the underlying conditions allowing it to flourish.
Understanding Dollar Weed and Cultural Controls
The presence of dollar weed indicates excessive moisture, as this aquatic perennial thrives in waterlogged soils and poorly drained areas where most turfgrass struggles. Long-term control depends on modifying the environment to favor your lawn over the invasive weed.
Shifting your watering schedule to deep and infrequent irrigation is the most impactful cultural change. Apply one to one and a half inches of water per week, allowing the soil surface to dry out completely between waterings. This practice encourages turfgrass to develop a deep root system while simultaneously stressing the shallow-rooted dollar weed.
Poor drainage, particularly in compacted soil, creates the moist environment dollar weed prefers. Aeration helps water penetrate deeper and reduces surface saturation. Adjusting your mowing height also creates a hostile environment, as taller turfgrass shades the soil surface. This shading prevents dollar weed seeds from germinating and limits sunlight available to existing plants, slowing their growth.
Targeted Chemical Solutions
When cultural practices are insufficient, selective post-emergent herbicides offer a direct method of control. These chemicals target the dollar weed without causing widespread damage to the surrounding turfgrass. Effective herbicides contain active ingredients such as Atrazine, 2,4-D, Dicamba, and MCPP, often sold as three-way herbicides.
For warm-season grasses like St. Augustine and Centipedegrass, products containing Atrazine are recommended. Other options include Metsulfuron-methyl or products containing a blend of three active ingredients, such as those found in Celsius, which provide broad-spectrum weed control. Herbicides should be applied when dollar weed is actively growing in late spring or early summer, typically when temperatures are between 60 and 85 degrees Fahrenheit.
Because dollar weed leaves have a waxy cuticle that can repel herbicides, repeat applications are often necessary. Applying a non-ionic surfactant with the herbicide mixture helps the active ingredients adhere to and penetrate the leaf surface more effectively. Always confirm that the chosen chemical is safe for your specific type of turfgrass, as some common three-way herbicides can severely damage St. Augustinegrass.
Non-Chemical and Manual Removal Strategies
For those who prefer to avoid synthetic herbicides, several non-chemical methods manage smaller infestations. Manual removal is a viable option, but it requires diligent effort, as the entire root structure must be extracted. Since dollar weed spreads through underground rhizomes and tubers, leaving any part of the root network behind allows the plant to quickly regrow.
Spot treatments using highly concentrated horticultural vinegar offer a natural alternative. Horticultural vinegar typically contains 10 to 30 percent acetic acid and acts as a contact herbicide that burns the exposed foliage. Because it is non-selective, this method will also kill any desirable turf or plant material it touches.
Boiling water is another non-selective option that instantly kills the plant material it contacts, making it suitable for weeds in pavement cracks or isolated patches. Solarization is an alternative technique for small areas, involving covering the infested patch with clear plastic sheeting for several weeks during the hottest part of the year. The plastic traps solar heat, raising the soil temperature high enough to kill the dollar weed and its underlying rhizomes.