Dollar weed, also known as pennywort (Hydrocotyle spp.), is a persistent perennial weed that commonly invades flower beds and ornamental gardens. It spreads rapidly and is challenging to remove without harming surrounding plants. Successful elimination requires targeted physical removal, cultural adjustments to the growing environment, and, if necessary, cautious application of selective chemical controls.
Recognizing Dollar Weed and Its Environment
Dollar weed is easily identified by its distinctive leaves, which are round, glossy, and bright green, often resembling miniature lily pads. The edges are typically scalloped, and the stem attaches directly in the center of the leaf’s underside, giving it an umbrella-like appearance. This perennial weed is an aggressive spreader, utilizing seeds, an extensive network of underground stems (rhizomes), and tubers.
The presence of dollar weed indicates consistently wet or poorly drained soil, as it is a water-loving plant. Research has shown that reducing irrigation frequency can directly lead to a decrease in dollar weed density. The weed thrives in areas with excessive moisture, often colonizing low spots where water collects or compacted areas. Understanding this environmental preference is the first step toward effective control.
Manual and Cultural Eradication
Removing dollar weed by hand is the safest method for protecting desirable flowers and shrubs in a densely planted bed. This process requires patience because the weed’s survival depends on its rhizome system, which can extend several feet and sprout new plants. Simply pulling the leaves often leaves the underground parts intact, leading to rapid regrowth.
When manually removing plants, carefully dig beneath the weed to extract the entire chain of rhizomes and any associated tubers. Perform this task when the soil is damp, as the runners are less likely to break, allowing for a more complete removal. For weeds growing close to ornamentals, use a small hand trowel or weeding fork to isolate the dollar weed roots without disturbing the desirable plant’s root ball.
The most effective long-term solution involves changing the environment to make it inhospitable for the weed. Since dollar weed flourishes when soil moisture exceeds 70%, correcting drainage issues is paramount. Improving soil aeration by incorporating organic matter or aerating the bed helps water move through the soil profile more efficiently.
Adjusting irrigation practices is crucial, as most established flower beds require deep but infrequent watering. Instead of daily, shallow watering, aim to apply about one to one and a half inches of water per week, allowing the top layer of soil to dry out between sessions. This approach starves the shallow-rooted dollar weed while encouraging deeper root growth in your flowers.
Selective Chemical Control in Flower Beds
In cases of severe infestation, chemical control may be necessary, but it must be approached with caution in a flower bed. The primary concern is protecting surrounding ornamental plants from non-selective herbicides. Homeowners should seek out post-emergent broadleaf herbicides specifically labeled as safe for use around established landscape plants.
Products containing active ingredients like imazaquin or a mixture of 2,4-D, MCPP, and dicamba can be selective, targeting dollar weed without harming many ornamentals. Always verify the label for plant tolerance before application, as different flowers and shrubs react differently to these chemicals. Using a non-selective herbicide like glyphosate is also effective, but requires extreme care.
Glyphosate-based products kill any green plant tissue they contact, so direct application is essential. For targeted application, you can use a small paintbrush or foam applicator to paint the herbicide solution onto the dollar weed leaves, completely avoiding contact with nearby flowers. Alternatively, a spray application can be used if a protective barrier, such as cardboard or plastic sheeting, shields desirable plants from accidental drift.
Strategies for Long-Term Prevention
After initial eradication, the focus must shift to creating a hostile environment to prevent dollar weed from returning. A thick layer of organic mulch is one of the most effective physical barriers against weed germination. Applying mulch (such as wood chips or shredded bark) three to four inches deep will block the sunlight necessary for dollar weed seeds to sprout.
Mulch also helps regulate soil moisture by reducing surface evaporation, but keep it a few inches away from the stems of desirable plants to prevent rot. Since dollar weed can creep into beds from adjacent turf areas via rhizomes, installing a physical barrier along the perimeter can stop this spread. Materials like plastic edging or metal barriers placed several inches deep will help contain the weed’s underground runners.
Ongoing monitoring of soil moisture is the most important cultural practice for sustained prevention. Regularly check for low spots or areas of poor drainage that may be contributing to excessive wetness, and promptly address any pooling water. Immediately hand-pull any new dollar weed sprouts as soon as they appear to prevent them from establishing a new rhizome network.