Pennywort, commonly known as Dollarweed (Hydrocotyle spp.), is a pervasive, low-growing perennial weed that frequently infests lawns and gardens in warm, temperate regions. This aggressive plant spreads rapidly through underground stems (rhizomes) and by seed, making it difficult to control. Effectively managing pennywort requires a comprehensive strategy that addresses the underlying environmental factors allowing it to thrive. This guide provides methods for eliminating existing pennywort and implementing cultural practices to prevent its return.
Identifying Pennywort and Its Environment
Dollarweed is easily identified by its unique, bright green, round leaves that resemble miniature lily pads or small coins. The leaf margins are typically wavy, and a distinguishing feature is the stem attachment point, which is located directly in the center of the leaf, like an umbrella. This characteristic helps differentiate it from similar-looking weeds like dichondra, which has the stem attached at the leaf’s edge.
The presence of pennywort indicates excessive moisture, as it is a water-loving perennial. It thrives in areas with poor drainage, saturated soil, or those that receive frequent, shallow irrigation. These conditions create the ideal habitat for pennywort to establish and spread. The weed’s creeping stems root wherever their nodes touch the soil, creating a dense mat that quickly overtakes thin turf.
Non-Chemical Elimination Methods
For small, localized infestations, physical removal is a viable non-chemical method. When hand-pulling, it is crucial to remove the entire plant, including the roots and rhizomes. Any remaining underground stems can quickly regenerate a new plant. This method is best performed when the soil is moist, which allows for easier and more complete extraction of the root system.
Environmental manipulation offers an effective non-chemical approach by targeting the weed’s need for excessive moisture. Reducing the frequency of watering and ensuring the lawn receives no more than one inch of water per week is a primary step in cultural control. Allowing the soil to dry out between watering sessions stresses the pennywort while encouraging deeper root growth in desirable turfgrass. Localized solarization, which involves covering a small, heavily infested area with clear plastic sheeting, can also use heat to kill the plant and its rhizomes.
Effective Herbicide Applications
When dealing with large or widespread infestations, selective post-emergent herbicides are necessary to control the weed without harming the surrounding turfgrass. Products containing a combination of active ingredients like 2,4-D, dicamba, and mecoprop (MCPP) are highly effective broadleaf weed killers. These three-way herbicides are safe for use on common warm-season grasses such as Bermudagrass, Zoysiagrass, and St. Augustinegrass, though the label should always be checked for compatibility.
The application timing is important, as the herbicide must be applied when the pennywort is actively growing, typically in the late spring and early summer. Due to the plant’s waxy leaves, which repel liquid, a non-ionic surfactant should be added to the mixture. This helps the chemical adhere to the foliage and penetrate the plant tissue. Repeat applications are often required, as the plant’s robust rhizome system can allow it to recover from a single treatment.
For areas without desirable turfgrass or in landscape beds, a non-selective herbicide like glyphosate can be used for spot treatments. This chemical will kill any plant it contacts, so care must be taken to avoid drift onto surrounding plants. Pre-emergent herbicides containing ingredients like atrazine or prodiamine can also be applied in the early spring to prevent seed germination.
Preventing Recurrence
Long-term control relies on permanently altering the conditions that favor pennywort growth, shifting the focus to strengthening the turf. The most significant step in prevention is addressing poor soil drainage and excessive soil moisture. Regularly aerating the lawn helps alleviate soil compaction, which improves water penetration and reduces the standing water pennywort requires.
Establishing a dense, healthy lawn is the best defense against weed invasion, as thick turf crowds out the low-growing pennywort. This requires proper mowing at a height appropriate for the grass species, promoting deeper root growth and helping the grass shade the soil surface. Maintaining soil fertility through regular fertilization and pH management ensures the turfgrass is vigorous enough to outcompete the weed. In persistently wet areas, installing permanent drainage solutions, such as a French drain, may be necessary to eliminate the waterlogged condition.