The sight of purple weeds spreading across an otherwise green lawn can be frustrating for any homeowner. Eliminating these weeds requires a two-part strategy: accurately identifying the specific plant species and then applying the correct control method at the most effective time. This approach ensures that your efforts are efficient and do not inadvertently damage healthy turfgrass.
Identifying the Most Common Purple Lawn Weeds
The majority of purple-flowered weeds found in lawns are Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium purpureum), both members of the mint family. They are winter annuals or biennials, germinating in the fall, surviving winter, and then flowering and producing seeds in the spring before dying off. Both share the characteristic square stems common to the mint family.
Henbit has heart-shaped leaves with scalloped edges that are directly attached to the stem, particularly near the top where the flowers emerge. Its pink to purple tubular flowers grow in whorls at the leaf axils along the stem. Purple Deadnettle, while similar, has more triangular leaves attached by a short stalk (petiole), even at the top of the plant. The upper leaves of Deadnettle often have a noticeable purplish tint, which gives the plant its name.
A third possibility is Creeping Charlie (Glechoma hederacea), a perennial weed that spreads aggressively. Unlike the winter annuals, Creeping Charlie has kidney-shaped leaves and a creeping growth habit, rooting at the nodes as it spreads. Its purple-blue flowers appear in spring, and the plant emits a distinct minty odor when crushed. Identifying whether you have an annual or a perennial determines the long-term strategy, as perennials require more persistent control.
Immediate Non-Chemical and Manual Removal
For small patches, manual removal is an effective approach. Pulling is most successful when the soil is moist, allowing the entire root system to be extracted. It is important to remove the weed before it flowers and sets seed in the spring, as a single plant can produce hundreds of seeds.
For larger areas, smothering can be an option by covering the weeds with a thick layer of organic mulch or black plastic to block sunlight. Spot treatments can also use horticultural vinegar, which contains a higher concentration of acetic acid (typically 10% to 20%) than household vinegar. This high acidity acts as a contact herbicide, rapidly desiccating the foliage it touches. However, vinegar is non-selective and will damage any turfgrass it contacts, and it may not destroy the deeper roots of established weeds, requiring reapplication.
Selecting the Right Herbicide for Control
Chemical control offers a broad-scale solution for larger infestations, requiring selective products that will not harm the turfgrass. Since these are broadleaf weeds, a selective broadleaf herbicide is necessary, often containing active ingredients like 2,4-D, MCPP (mecoprop), and dicamba. These combination products, sometimes called “three-way” herbicides, are highly effective.
The timing of application is crucial and depends on whether you choose a pre-emergent or post-emergent product. Pre-emergent herbicides are preventive and must be applied before the weed seeds germinate. For winter annuals like Henbit and Deadnettle, the application window is in the early fall, ideally when the soil temperature drops consistently to around 70 degrees Fahrenheit. This timing creates a chemical barrier that prevents germination.
Post-emergent herbicides are applied directly to visible, actively growing weeds. For winter annuals, the most effective time for treatment is in the late fall or early spring when temperatures are cool but above 50 degrees Fahrenheit, ensuring the weeds are metabolically active. Applying treatments when the weeds are young and small significantly increases success. Always ensure the herbicide label states it is safe for your specific type of turfgrass and follow all application instructions.
Long-Term Strategies to Prevent Recurrence
The presence of purple weeds indicates the lawn environment is favorable for their growth, suggesting that improving overall turf health is the best long-term prevention. Promoting a dense, vigorous stand of turfgrass creates natural competition that minimizes the space and sunlight available for weed seeds to germinate. This cultural control approach is fundamental to a sustainable, weed-resistant lawn.
One effective strategy is maintaining an optimal mowing height, which for most cool-season grasses ranges between 3 and 4 inches. Taller grass blades cast shade onto the soil surface, preventing the sunlight necessary for weed seed germination. The increased leaf surface allows the grass to generate more energy, promoting deeper, healthier root growth that outcompetes shallow-rooted weeds.
Proper watering practices also play a role, as deep and infrequent irrigation promotes deep turfgrass roots while discouraging surface-level weed growth. Periodically conducting soil testing can reveal nutrient deficiencies or imbalances, such as incorrect pH levels, which can be corrected with targeted fertilization. Aeration helps reduce soil compaction, allowing turf roots to penetrate deeper and improving drainage, making the environment less hospitable to weeds.