Oxalis, commonly known as wood sorrel, is a persistent lawn weed that challenges homeowners. This low-growing plant is difficult to manage due to its aggressive reproductive strategies and resilience in various turf conditions. Eradicating a mature Oxalis infestation requires a comprehensive, multi-step approach combining cultural practices with targeted chemical treatments. The goal is to remove existing plants and disrupt the weed’s ability to spread by both seed and root systems.
Understanding Oxalis Identification and Growth
Oxalis is often mistaken for clover due to its trifoliolate leaves, but a closer look reveals leaflets that are distinctly heart-shaped, sometimes displaying a bronze or purple hue. The plant produces small, bright yellow flowers, typically with five petals, which bloom from spring through the warmer months. Identifying the plant’s growth habit is the first step toward effective control, as it uses two primary methods to spread aggressively.
The most notorious reproductive mechanism is the explosive seed pod. When the capsule matures, it bursts open, flinging tiny reddish-brown seeds up to 16 feet away from the parent plant. This ensures widespread distribution across the lawn, making immediate removal upon sighting the flowers necessary. Furthermore, many Oxalis species, such as Oxalis corniculata, spread laterally by creeping stems called stolons or by underground rhizomes. This root structure often includes small bulbils that readily break off during manual removal, allowing the plant to quickly regrow from the remaining fragments.
Non-Chemical and Cultural Control Methods
Physical removal of Oxalis is an option for very small, isolated patches, but it must be done with care to prevent re-sprouting. The entire taproot and any attached bulbils or rhizomes must be meticulously removed from the soil. If root fragments remain, the plant can regenerate, which is why hand-pulling often proves frustrating and ineffective for larger infestations.
Cultural control methods focus on creating a dense, healthy turf that naturally crowds out the weed. Proper mowing height is an effective strategy, as Oxalis requires light to germinate. Keeping the turfgrass relatively tall, generally around three inches, shades the soil surface and inhibits the germination of new seeds.
Altering irrigation practices also shifts the environment in favor of turfgrass over Oxalis. A deep, infrequent watering schedule encourages the turf roots to grow deeper, increasing the lawn’s density and overall health. This practice reduces the surface moisture that Oxalis seeds prefer for quick germination, limiting its ability to establish.
Selecting Effective Herbicides for Oxalis
Chemical control is often necessary for established or widespread Oxalis infestations, requiring a two-pronged attack using both pre-emergent and post-emergent herbicides. Post-emergent herbicides target the visible, actively growing weeds by applying the chemical directly to the foliage. Oxalis is notably resistant to many standard broadleaf weed killers that rely solely on 2,4-D.
Effective post-emergent control requires combination products that include active ingredients like triclopyr, dicamba, or fluroxypyr, often blended with 2,4-D and MCPP. Triclopyr is particularly effective against hard-to-kill broadleaf weeds such as Oxalis. Care is needed when applying it to some warm-season grasses like Bermudagrass due to potential phytotoxicity. Applying these systemic herbicides when the Oxalis is young and actively growing—typically in late spring or when temperatures are below 90°F—maximizes absorption throughout the plant’s system.
Pre-emergent herbicides are equally important for long-term control because they prevent the seeds from germinating. Products containing active ingredients like prodiamine create a chemical barrier at the soil line that stops seedlings before they emerge. Since Oxalis seeds can germinate nearly year-round, applying a pre-emergent in the late winter or early spring targets the bulk of the new growth. Pre-emergent applications do not affect existing mature plants or those emerging from the underground rhizomes, which is why they must be paired with post-emergent treatments.
Long-Term Strategies for Prevention
Successful long-term prevention centers on maintaining a dense, healthy lawn environment that actively resists re-infestation. Soil health is a foundational element; conducting a soil test to determine pH and nutrient levels allows for targeted fertilization and liming. Ensuring the turf is well-fed and has a balanced pH encourages vigorous growth, which closes the canopy and leaves less space and light for weeds to exploit.
Overseeding the lawn regularly, especially in thin or heavily infested areas, increases the overall turf density. A thick stand of desirable turfgrass acts as a living mulch, shading the soil and physically preventing Oxalis seeds from reaching the light they need to germinate. This increased competition for resources reduces the opportunity for stray seeds to take hold.
Vigilance is necessary to catch new outbreaks early. Homeowners should routinely inspect the lawn for the earliest signs of the characteristic heart-shaped leaves or yellow flowers. Spot treating newly emerged Oxalis plants with a targeted post-emergent herbicide before they set seed will prevent the explosive spread. Consistent application of these cultural and chemical strategies is the path to sustained control.