Dollar weed, also known as pennywort, is a persistent perennial weed that can quickly colonize a healthy lawn. This aggressive plant is a warm-season invader, often indicating a lawn environment overly favorable to its growth. Successfully eliminating dollar weed requires a targeted, two-pronged approach: combining selective chemical treatments with adjustments to your lawn care routines to ensure the surrounding turfgrass remains unharmed.
Identifying the Target: The Biology of Dollar Weed
Dollar weed, scientifically classified as Hydrocotyle spp., is easily recognized by its distinctive foliage. The leaves are bright green, glossy, and perfectly round with scalloped edges, resembling miniature lily pads or small coins, which gives the plant its common name. A key identifying feature is the stem, or petiole, which attaches directly to the center of the leaf, creating an umbrella-like appearance.
The plant’s difficulty in eradication stems from its extensive underground network. Dollar weed spreads not only by seeds but also through rapidly growing horizontal underground stems (rhizomes) and storage structures (tubers). This complex root system allows it to quickly spread and makes simple hand-pulling ineffective, as leaving behind even a small fragment can lead to regrowth.
Dollar weed is a moisture-loving species, and its presence indicates excessive water in the lawn environment. It thrives in poorly drained, wet, or compacted soil and often colonizes areas where water pools or irrigation is excessive. The weed is particularly active during warm growing seasons when soil temperatures are above 65°F, allowing it to outcompete thin or stressed turfgrass.
Selective Chemical Solutions That Spare Turfgrass
When cultural controls are not enough to manage a significant infestation, selective herbicides offer a precise method for eliminating dollar weed without harming the turfgrass. The most effective products for post-emergent control are those containing a combination of broadleaf-targeting active ingredients. These ingredients are designed to disrupt the growth hormones of broadleaf weeds while leaving grasses unaffected.
Look for formulations that include 2,4-D, MCPP (Mecoprop), and Dicamba, often sold as a “three-way” broadleaf herbicide. These compounds are systemic, meaning they are absorbed through the leaves and travel down to the rhizome and tuber system, ensuring the entire plant is targeted. Metsulfuron is another active ingredient highly effective against dollar weed, though its use requires careful adherence to label instructions based on turf type.
Proper application timing and method are necessary for chemical control to be successful. Herbicides should be applied when the dollar weed is actively growing, typically when temperatures are consistently between 60°F and 85°F. Spot treatment using a pump sprayer is highly recommended for isolated patches to minimize the amount of chemical applied to the lawn overall.
Since dollar weed is a perennial with a robust underground system, a single application is rarely sufficient for total control. Two or three applications spaced approximately 10 to 14 days apart are often required to ensure that new growth emerging from tubers is also treated. Always verify that the chosen product is labeled as safe for your specific type of turfgrass (e.g., St. Augustine, Bermuda, or Zoysia), as not all grasses tolerate every broadleaf herbicide equally.
Cultural Practices for Suppression and Removal
To support chemical efforts and prevent re-infestation, modifying the local environment is a powerful non-chemical strategy. Dollar weed’s preference for saturated soil means that correcting moisture issues is the primary step toward suppression. This involves adjusting your irrigation schedule to water deeply but infrequently, avoiding shallow, frequent watering that keeps the soil surface perpetually moist.
The goal is to provide turfgrass with the recommended one to one-and-a-half inches of water per week, allowing the top layer of soil to dry out between watering sessions. This cycle encourages the grass to develop deeper roots while creating an unfavorable, drier environment for the dollar weed. Improving soil drainage is also important; this may involve core aeration to alleviate compaction, allowing water to penetrate the soil more effectively instead of pooling on the surface.
For small, manageable patches, manual removal remains a viable option, but it must be executed with precision. When hand-pulling, it is imperative to remove the entire root structure, including the attached rhizomes and tubers, as any fragments left behind can sprout into new plants. The best time to attempt physical removal is when the soil is damp, which makes the extensive underground network easier to extract intact.
Maintaining a Weed-Free Lawn Environment
After controlling the initial dollar weed outbreak, long-term prevention focuses on promoting a dense, vigorous turf that naturally crowds out new weed growth. Proper mowing height plays a significant role in this preventative strategy. Mowing the grass at the higher end of its recommended height range (e.g., 3 to 4 inches for St. Augustinegrass) creates a canopy that shades the soil surface, blocking the sunlight needed for dollar weed seeds and new sprouts to germinate.
A well-nourished lawn can effectively outcompete weeds, so adopting a balanced fertilization program is necessary. Conducting a soil test can determine any nutrient deficiencies or pH imbalances, which, if corrected, strengthen the turf’s density and root system. Dense turf prevents the weed from finding open patches of soil in which to establish itself, transforming the lawn into a natural barrier.
Finally, pre-emergent herbicides can be used to prevent new dollar weed growth from seeds or tubers. These products, which often contain active ingredients like Prodiamine, create a chemical barrier in the soil that inhibits the sprouting process. Application is typically recommended in the early spring, before the soil warms and the growing season begins, to stop the cycle of re-infestation.