Pennywort, often called dollarweed due to its leaf shape, is a common and aggressive perennial weed that quickly takes over lawns. This resilient plant is difficult to control because it spreads rapidly and thrives in wet environments. Eliminating pennywort requires a multi-faceted approach that addresses both the existing weeds and the underlying lawn conditions allowing it to thrive.
Identifying Pennywort and Its Growth Habits
Pennywort is easily recognizable by its bright green, rounded leaves with scalloped edges, resembling small coins. The leaf stem (petiole) attaches directly to the center of the leaf, giving it an umbrella-like appearance. This feature differentiates it from other weeds like dichondra, where the stem attaches to the leaf’s edge.
As a perennial, pennywort spreads through seeds and a network of creeping underground stems called rhizomes and tubers. These structures allow the plant to form dense mats, making manual removal challenging since fragments lead to rapid regrowth. Pennywort thrives in wet conditions, and its robust growth indicates excessive soil moisture, poor drainage, or over-irrigation.
Non-Chemical Removal and Cultural Adjustments
For small, isolated patches, manual removal is effective if the entire root and rhizome system is extracted. Hand-pulling is easiest when the soil is moist, allowing complete removal of the fragile underground runners. Thoroughness is important to prevent reinfestation.
The most effective non-chemical control involves altering the environmental conditions that favor the weed. Reducing irrigation frequency is a primary step, as pennywort thrives in saturated conditions. Aim to provide about one inch of water per week, including rainfall, to prevent soggy soil. This stresses the pennywort while promoting deeper root growth in the turfgrass.
Improving soil drainage directly targets the weed’s preferred habitat. Raising the lawn mower height helps the turfgrass grow thicker and denser. Taller, healthier grass creates shade at the soil level, suppressing pennywort by blocking the sunlight it needs to thrive.
Targeted Herbicide Treatment Strategies
For widespread or established pennywort infestations, targeted herbicide applications are the most practical solution for control. Post-emergent, selective herbicides are required, which treat existing weeds without harming the surrounding turfgrass. These products typically contain active ingredients such as 2,4-D, dicamba, and MCPP, often combined in a “three-way” formula.
The specific herbicide choice depends on your grass type, as some turf varieties are sensitive to certain chemicals. St. Augustine and Centipede grasses are sensitive to 2,4-D and dicamba; for these lawns, a product containing atrazine is generally a safer and more effective option. Atrazine is not recommended for use on Bermuda grass, which tolerates the three-way herbicide mixtures.
Application timing is crucial for maximizing the herbicide’s effectiveness and should occur when the pennywort is actively growing, typically in the late spring. Optimal temperatures for application are between 65 and 85 degrees Fahrenheit. Because the weed spreads extensively via rhizomes, a single treatment is rarely enough to eliminate the problem completely. A second application 10 to 14 days later is required to kill any new growth. Always read the product label thoroughly to ensure compatibility with your turfgrass and follow all safety and application instructions, as misapplication can damage your lawn or nearby ornamental plants.
Long-Term Prevention Through Turf Management
Once the existing pennywort has been managed, the focus must shift to creating a dense, healthy turf that resists future weed invasion. A robust lawn is the best long-term prevention measure, as it outcompetes weeds for light, water, and nutrients. Proper fertilization schedules are a cornerstone of this strategy, providing the lawn with the nutrients it needs to grow thickly and fill in any bare patches where pennywort might establish itself.
Aeration is a vital practice, especially where poor drainage or soil compaction is a contributing factor to the pennywort problem. Core aeration removes small plugs of soil, which helps to relieve compaction and improves the movement of water and air into the root zone. This directly combats the waterlogged conditions that pennywort favors, making the environment less hospitable for its return.
Overseeding the lawn with desirable grass varieties is an effective technique to increase turf density. By introducing new seeds into thin areas, you create a thicker stand of grass that physically blocks sunlight from reaching the soil surface, thus preventing weed seed germination. Soil testing can also provide valuable data, revealing any underlying nutrient deficiencies or pH imbalances that may be weakening your turf and making it susceptible to weed invasion.