The appearance of small purple flowers or reddish-purple foliage in a lawn can be a confusing sight for homeowners, especially during the cool temperatures of early spring or late fall. This growth is a sign that a broadleaf weed has successfully invaded the turfgrass, taking advantage of conditions that favor its growth cycle. These low-growing invaders are often winter annuals that germinate in the fall and survive the winter as small seedlings, only to flower and set seed quickly once temperatures rise. Accurately identifying the specific plant is the necessary first step because different weeds require specialized management techniques for effective control. This article will help to identify the three most frequent culprits and provide actionable strategies for managing them now and preventing their return in the future.
Identifying the Common Purple Invaders
One of the most frequent purple weeds to appear in lawns is Purple Deadnettle (Lamium purpureum), which is easily recognized by the dense cluster of reddish-purple leaves at the top of its upright stem. The plant is a member of the mint family and possesses the characteristic square-shaped stem. Its leaves are heart-shaped or triangular with scalloped edges and are attached to the stem by short stalks, particularly near the top of the plant. Small, tubular pink-to-purple flowers emerge from the leaf axils near the apex of the stem, often blooming vigorously in the early spring before the turfgrass fully greens up.
A close relative often confused with Purple Deadnettle is Henbit (Lamium amplexicaule). Henbit also features the square stem and small purplish-pink flowers arranged in whorls around the stem. However, its upper leaves are directly attached to the stem without a stalk. The leaves of Henbit are more rounded or kidney-shaped with bluntly toothed margins, and while the stems may be purplish, the upper foliage typically lacks the vibrant reddish-purple tinge seen in Purple Deadnettle. Both of these species are winter annuals and typically die off completely as summer heat arrives.
Creeping Charlie or Ground Ivy (Glechoma hederacea) is a perennial weed with a very different growth habit. Unlike the erect growth of the annuals, Creeping Charlie forms dense, low-growing mats of stems that creep along the ground, rooting at each node. The leaves are rounded or kidney-shaped with scalloped edges, and they are attached to the stem by long petioles. A reliable way to confirm its identity is by crushing a leaf, which releases a strong minty aroma. Creeping Charlie produces small, tubular, bluish-purple flowers in the spring, but its aggressive, vine-like spread and perennial nature make it much more persistent than the two annual species.
Environmental Factors That Encourage Growth
The presence of these purple-flowered weeds indicates underlying issues with the soil or the overall health of the turfgrass. Winter annuals like Henbit and Purple Deadnettle take advantage of thin turf cover that allows sunlight to reach the soil, triggering seed germination in the fall. A dense, healthy lawn naturally crowds out weeds by minimizing the light available to weed seeds and seedlings.
Many of these weeds, especially Creeping Charlie, flourish in areas with moisture, poor soil drainage, or shade. Moist conditions and compacted soil can stress turfgrass roots, making the lawn less competitive against weeds. Creeping Charlie, in particular, is highly tolerant of shaded areas, often establishing itself under trees where turfgrass struggles to grow.
Soil fertility and pH levels also play a role in promoting weed growth over desirable turf. Low soil fertility and an unfavorable pH can weaken the grass, creating an opportunity for weeds that tolerate these less-than-ideal conditions. The winter annuals germinate and grow during the turf’s dormant period, allowing them to establish before the grass can resume active growth in the spring.
Strategies for Long-Term Removal
Long-term management involves a combination of cultural practices that strengthen the lawn and targeted chemical controls. The most effective defense against all weeds is maintaining a thick, vigorous turf that leaves no space for weed seeds to germinate. Simple cultural practices, such as raising the mowing height, encourage the grass to grow denser and help shade the soil, preventing weed seeds from receiving the light they need to sprout.
Correcting soil issues like compaction can be accomplished through core aeration to improve drainage and encourage deeper grass root growth. Overseeding thin areas of the lawn in the fall will increase the turf density. Proper watering, which involves deep but infrequent applications, promotes strong grass roots, making the turf more drought-resistant and competitive against shallow-rooted weeds.
For existing, widespread infestations, chemical control is often a necessary component, with the timing of application being important. A pre-emergent herbicide applied in the late summer or early fall will prevent the seeds of winter annuals from germinating. Post-emergent broadleaf herbicides containing active ingredients like 2,4-D, MCPP, and Dicamba are effective on actively growing weeds in the early spring. Creeping Charlie is one of the more challenging weeds to eliminate and often requires specialized broadleaf herbicides that contain triclopyr or sulfentrazone. Herbicide applications are most effective when applied in the fall, as the perennial weed is actively moving energy reserves to its roots for winter storage, which pulls the chemical deep into the plant’s system.