How to Kill Pennywort and Prevent It From Returning

Killing pennywort requires a combination of reducing the excess moisture it thrives on, removing or chemically treating existing growth, and changing the conditions that invited it in the first place. Pennywort is not one single plant but a group of low-growing, round-leaved species in the Hydrocotyle and Centella genera, and the approach you take depends on whether it has colonized your lawn, your garden beds, or a pond. What makes it frustrating is that it spreads by underground stems (rhizomes or stolons) and can regenerate from small fragments left behind, so a one-time treatment rarely solves the problem for good.

Which Pennywort Are You Dealing With

Before reaching for a product or a shovel, it helps to know which species has moved in. In the southeastern United States, the most common lawn invader is Hydrocotyle umbellata, widely called dollarweed because of its round, silver-dollar-shaped leaves on upright stalks. It thrives in warm, wet turf and is the variety most homeowners are Googling about. In cooler or transitional climates, Hydrocotyle sibthorpioides (lawn marshpennywort) shows up instead, with smaller, scalloped leaves that hug the ground more tightly. Both are native or naturalized and behave similarly in lawns.

Floating pennywort (Hydrocotyle ranunculoides) is a different beast entirely. Originally from the Americas, it has become a serious aquatic invasive in the United Kingdom and parts of continental Europe, forming dense mats on canals, rivers, and ponds. Its rapid and thick growth can block watercourses and disrupt both boat traffic and wildlife habitat.¹ If your problem is a mat of pennywort spreading across a water feature, the control strategy is quite different from the lawn approach.

Finally, Centella asiatica (Asiatic pennywort or gotu kola) appears in warm-climate lawns and is sometimes cultivated intentionally as a ground cover or herbal remedy. Its leaves look similar to dollarweed but sit a bit flatter, and it has a long history of culinary and medicinal use in Southeast Asia. Whether you want to kill it or eat it depends on your perspective, but it is worth identifying correctly before you spray.

Manual and Mechanical Removal

Hand-pulling pennywort works for small patches if you commit to getting the roots. The plant spreads through underground runners, so yanking the visible leaves while leaving a web of stolons in the soil just encourages it to fill back in within a few weeks. Use a garden fork or a hand weeder to loosen the soil around the patch, then pull steadily, trying to extract as much of the runner system as you can. Work when the soil is damp (but not waterlogged), which makes it easier to pull runners intact rather than snapping them off.

For larger infestations in garden beds, smothering with a thick layer of cardboard topped by mulch can starve the plant of light. This takes patience. You will need to leave the barrier in place for at least a full growing season and check periodically for runners that escape around edges. Landscape fabric alone is less effective because pennywort stolons are thin enough to find gaps and poke through seams over time.

In lawns, mechanical removal is mostly impractical once the weed has spread widely. A few scattered patches can be dug out and the bare spots reseeded or plugged with turf, but if dollarweed covers more than about a quarter of the yard, you are better off addressing the underlying moisture problem and using targeted herbicides.

Why Moisture Is the Real Problem

Pennywort is not a random invader. It is a moisture indicator. Its presence in your lawn is a signal that the soil stays wetter than your turf grass prefers, whether from overwatering, poor drainage, or compacted soil that holds water near the surface. Fix the moisture, and you take away the pennywort’s competitive advantage.

Research on dollarweed in St. Augustinegrass turf demonstrated this starkly. Plots watered daily had roughly 30 percent dollarweed cover. Plots watered on a conditional weekly schedule, where irrigation was triggered only when the turf showed early signs of drought stress, had just 6 percent cover. And plots where irrigation was withheld until the turf was severely wilted dropped to about 2 percent dollarweed cover.² That is a fifteen-fold difference in weed cover, achieved entirely by watering less.

The practical takeaway is straightforward: if you water your lawn on a fixed daily schedule, switch to an as-needed approach. Water deeply but less frequently, allowing the top inch or two of soil to dry between sessions. Most warm-season grasses are more drought-tolerant than their owners give them credit for, and letting the soil surface dry out makes conditions hostile for pennywort while barely inconveniencing the turf.

If your yard stays wet regardless of irrigation, you likely have a drainage problem. Low spots that pool after rain, soil that has been compacted by foot traffic or construction, or clay-heavy subsoil can all hold moisture in the root zone long after the surface looks dry. Core aeration in spring or fall helps compacted lawns. For persistent low spots, regrading or installing a French drain may be the only long-term fix. These are bigger projects, but no herbicide will keep pennywort away permanently if the ground stays soggy.

Chemical Control in Lawns

Herbicides are the fastest way to knock back an established pennywort population, though they work best as one piece of a larger strategy that includes the cultural changes described above. The specific products you can use depend on what type of turf you have, because some herbicides that are safe on one grass species will damage another.

For warm-season lawns (St. Augustinegrass, bermudagrass, zoysiagrass, bahiagrass, and centipedegrass), the most commonly recommended active ingredients for dollarweed include broadleaf herbicides containing combinations of 2,4-D, dicamba, and MCPP (mecoprop). These three-way herbicide blends are widely available at garden centers under various brand names and are labeled for dollarweed on most warm-season turf types. Always check the label for your specific grass, because some formulations are not safe on centipedegrass or St. Augustinegrass.

Atrazine is another option for certain warm-season grasses, particularly St. Augustinegrass and centipedegrass in states where it is still available for residential use. It works both as a pre-emergent and post-emergent on dollarweed, but it should not be applied near water bodies, and some municipalities restrict its use because of concerns about groundwater contamination.

For cool-season lawns (tall fescue, Kentucky bluegrass, perennial ryegrass), standard broadleaf herbicides containing triclopyr or 2,4-D plus dicamba are effective. Pennywort is less common in cool-season turf because these lawns tend to grow in climates that are drier or cooler, but in transitional zones or chronically wet areas it can still show up.

Timing matters as much as product choice. Pennywort is most actively growing and most susceptible to herbicide uptake when temperatures are warm and the plant is not drought-stressed. In most of the southeastern U.S., late spring through early summer is the ideal window. Apply on a day when rain is not expected for at least 24 hours and the wind is calm. A repeat application two to three weeks later is often necessary because the rhizome network can survive the first round and send up new growth.

Non-selective herbicides like glyphosate will kill pennywort, but they will also kill the surrounding turf, so they are only practical for spot treatment of dense patches in garden beds, sidewalk cracks, or areas you plan to resod. In a lawn setting, stick with selective broadleaf herbicides that leave the grass intact.

Mowing Height and Fertilization

While herbicides and irrigation changes get most of the attention, mowing and fertilization also influence how competitive your turf is against pennywort. A thick, healthy lawn shades the soil surface and physically crowds out weed seedlings, including pennywort.

Mowing your grass at the higher end of its recommended range helps. For St. Augustinegrass, that means around 3.5 to 4 inches. For bermudagrass maintained as a home lawn (not a golf green), 1.5 to 2 inches. Taller grass casts more shade on the soil, which suppresses both weed seed germination and the lateral spread of pennywort stolons. Cutting too short opens up the canopy and lets light reach the ground, giving pennywort room to establish.

Fertilization should match your grass’s actual needs rather than following a maximalist schedule. Over-fertilizing, especially with quick-release nitrogen, can push excessive top growth that then requires more frequent mowing, stresses the turf, and creates an unstable canopy. A soil test will tell you what your lawn actually needs. In many cases, pennywort-prone lawns benefit more from potassium (which helps the grass handle moisture stress) than from additional nitrogen.

Controlling Pennywort in and Around Water

Floating pennywort in ponds, streams, and canals is a different challenge from lawn dollarweed. Because the plant floats and roots at nodes along its stems, fragments that break off during removal can drift downstream and start new colonies. Mechanical removal with rakes, weed harvesters, or even excavators is the primary approach in waterways, but it needs to be done carefully to capture as many fragments as possible.

In the UK, where Hydrocotyle ranunculoides is a Schedule 9 invasive species, it is actually illegal to allow it to spread into the wild. Management programs combine repeated physical removal with follow-up herbicide treatment using approved aquatic herbicides. Glyphosate formulations approved for use near water are the most common choice, but they require application by trained operators who can control drift and avoid killing non-target vegetation along the bank.

For a backyard pond, the most practical approach is to physically remove as much of the mat as you can, bag it (do not compost it where fragments could wash back in), and then reduce the nutrient load that feeds it. Pennywort in ponds is usually a symptom of nutrient-rich water from lawn fertilizer runoff, fish waste, or decomposing organic matter on the bottom. Reducing fertilizer applications near the pond edge, adding barley straw bundles to slow algae and nutrient cycling, and installing a buffer strip of taller vegetation between the lawn and the water can all help starve the plant of the nitrogen and phosphorus it needs.

Biological Control

For floating pennywort specifically, researchers have studied natural enemies from the plant’s native range in South America. Field work in Argentina found that two organisms in particular seemed to play a role in the decline of individual pennywort patches: a weevil (Listronotus elongatus) and a fungal pathogen (Cercospora sp.). The patches only recovered and regrew when densities of these natural enemies were at their lowest, and sampling showed a negative correlation between plant biomass and the extent of feeding and disease damage.¹ Competitor plants and climate, by contrast, had little bearing on whether patches survived.

The weevil has been investigated as a classical biological control agent for release in countries where floating pennywort is invasive. As of the early 2020s, host-specificity testing and risk assessments have been underway, but regulatory approval for release in the UK and Europe has been slow and cautious, as it should be for any non-native insect introduction. For the average homeowner, biological control of pennywort is not yet something you can buy off a shelf. It remains a research-stage approach, mostly relevant to large-scale waterway management.

In lawns, there is no practical biological control for dollarweed. No commercially available insect, fungus, or grazing animal selectively targets Hydrocotyle in turf without causing other problems. The “biological control” for lawn pennywort is really just a thick, competitive turf stand grown under the right cultural conditions: the grass itself is the biocontrol agent, outcompeting the weed when conditions favor grass over pennywort.

Common Mistakes That Let Pennywort Return

People often treat pennywort like a one-and-done problem. They spray an herbicide, watch the visible growth die back, and consider the job finished. But the underground runner system is extensive and can survive a single herbicide application, especially if the product was applied at the wrong time or in cooler weather when the plant was not actively growing. Without a follow-up treatment and a change in watering habits, new shoots typically appear within a month or two.

Another common mistake is relying on pre-emergent herbicides alone. Pre-emergents work by preventing seeds from germinating, but most pennywort spread in lawns is vegetative, through stolons and rhizome fragments rather than from seed. A pre-emergent barrier does almost nothing to stop an existing colony from expanding. Post-emergent herbicides that kill the actively growing plant are what you need for an established infestation.

Overwatering after treatment is the third big pitfall. If you spray an effective herbicide and then continue watering your lawn every day, you have removed the symptom but not the cause. The conditions that favored pennywort are still there, and either the same colony or new plants from seed or fragments will recolonize quickly. The irrigation data from turf research bears repeating in spirit here: the difference between daily watering and stress-based watering was a fifteen-fold reduction in dollarweed cover, entirely without herbicides.²

Is Pennywort Edible, and Does That Change Anything

Some species of pennywort are edible and have a long history of use in traditional medicine and cooking. Centella asiatica (gotu kola or Asiatic pennywort) is eaten fresh in salads and drinks across Southeast Asia and is used in herbal preparations said to support wound healing and cognitive function. Hydrocotyle species are also sometimes foraged, though they are less widely consumed.

If you are tempted to eat the pennywort growing in your yard rather than kill it, there are a few things to consider. First, make sure you have correctly identified the species. Centella asiatica and Hydrocotyle species look similar to the untrained eye, and misidentification of wild plants carries real risk. Second, and more importantly, pennywort growing in urban or suburban soil can accumulate heavy metals. A study of Centella asiatica grown in contaminated soils in Malaysia found that the plants took up elevated levels of zinc and nickel, and the potential for lead toxicity was high enough that daily consumption from polluted sites was not recommended.³ Lawns treated with herbicides, pesticides, or synthetic fertilizers are obviously also not a safe source of anything you plan to eat.

For most homeowners, the answer is straightforward: if pennywort is taking over your lawn and you did not plant it there, it is a weed, and the goal is removal. If you want to grow gotu kola intentionally as a ground cover or culinary herb, give it its own raised bed with clean soil, keep it away from treated turf, and treat it like any other garden herb rather than letting it run wild across the yard.