Dollarweed, a common lawn pest also known as Pennywort (Hydrocotyle spp.), is a persistent problem for homeowners, especially in warm, moist climates. In most regions, the answer is that Dollarweed does not die in winter but instead enters a state of dormancy. The above-ground foliage may perish with the first hard frost, giving the appearance that the problem has been solved. This perennial weed, however, possesses specialized underground structures that allow it to survive periods of cold and quickly re-emerge when temperatures rise again.
Identifying Dollarweed and Its Life Cycle
Dollarweed is easily recognized by its distinctive, bright-green, round leaves, which are often described as miniature lily pads or silver dollars. The leaves typically have scalloped edges, and a key identifier is that the leaf stem, or petiole, attaches directly to the center of the underside of the leaf, like an umbrella. This low-growing plant spreads aggressively, forming dense patches that can quickly overtake turfgrass.
Dollarweed is classified as a perennial weed, contributing significantly to its persistence. It thrives in conditions of excessive moisture, often signaling poor drainage or overwatering. Its preference for wet soil and ability to tolerate a range of light conditions, from full sun to partial shade, make it a formidable competitor against turfgrass. The plant reproduces through seeds, but its primary means of spreading involves underground stems and specialized root structures.
Dollarweed’s Winter Survival Strategy
While the visible, above-ground leaves of Dollarweed will turn brown and die following a significant drop in temperature, the plant is not truly dead. This die-back is simply the plant entering a dormant phase, which is a defensive measure against cold and lack of moisture. Survival is ensured by a robust network of underground storage organs: rhizomes and tubers.
Rhizomes are horizontal underground stems that allow the plant to spread laterally, and tubers are swollen, nutrient-storing root structures. These structures are packed with stored carbohydrates and energy reserves, which insulate the plant and sustain it through the winter months. The stored energy allows the plant to wait out the cold period and ensures a vigorous and rapid re-emergence of new growth as soon as the soil temperatures warm in the spring.
In the most northern parts of its hardiness range, which extends from USDA zones 5 to 10, prolonged, deep-freezing conditions may kill the underground structures. For most regions where Dollarweed is a nuisance, the cold is not sustained enough to penetrate the soil deeply enough to destroy the rhizomes and tubers. This biological mechanism makes complete eradication through natural winter conditions highly unlikely in areas with mild winters.
Effective Control and Prevention Methods
Controlling Dollarweed requires addressing both the plant’s biology and the environmental conditions it prefers. The most fundamental step is cultural control, which involves correcting excessive moisture. Reducing irrigation frequency, ensuring the lawn receives about one inch of water per week, and improving soil drainage are necessary for long-term suppression.
Maintaining a healthy, dense lawn is a highly effective preventive measure, as strong turf can outcompete the weed. Mowing at the proper height encourages deeper root systems and shades the soil, which helps prevent Dollarweed seeds from germinating.
Chemical Control
Systemic post-emergent herbicides are recommended because they are absorbed by the foliage and translocated down to the energy-storing rhizomes and tubers. These herbicides are most effective when the Dollarweed is actively growing in the spring, summer, or fall, as the plant is actively transporting nutrients throughout its system. Chemical treatments applied during winter dormancy when the foliage is dead will be ineffective.
Physical Removal
Physical removal is possible for small infestations, but it is necessary to thoroughly dig out all rhizomes and tubers to prevent immediate regrowth.