Henbit (Lamium amplexicaule) and purple deadnettle (Lamium purpureum) are aggressive winter annual weeds that frequently invade lawns and garden beds, becoming noticeable with their rapid growth and purple flowers in early spring. These weeds germinate in the fall, survive the winter as small plants, and explode in size during the first warm days, often creating dense mats that smother desirable turf and plants. Waiting until the spring bloom makes eradication more challenging, as the plants are already preparing to set the seeds that will fuel next year’s infestation. Understanding the differences between these two similar weeds and applying the correct control method at the right time is the most effective path to a clear landscape.
Accurate Identification of Henbit and Purple Deadnettle
Henbit and purple deadnettle are closely related members of the mint family, both exhibiting the characteristic square stems. Despite their similarity, observing the leaves provides the most reliable distinction between the two species. Henbit leaves are rounded or heart-shaped with scalloped edges, and the upper leaves lack a stalk, appearing to wrap directly around or “clasp” the main stem.
In contrast, purple deadnettle leaves are more triangular or spade-shaped and have a distinct petiole, or stalk, connecting them to the stem, even near the top of the plant. Purple deadnettle also gets its name from the upper leaves and stems, which frequently display a prominent reddish or purplish tint, especially in cooler weather. Both produce small, pink-to-purple, tubular flowers clustered at the tips of the stems.
Non-Chemical Removal Techniques
For small or isolated infestations, physical removal offers a successful non-chemical solution that immediately eliminates the plant and prevents seed production. Hand-pulling is effective, particularly because both weeds have relatively shallow root systems. It is important to remove the entire plant, including the root, to prevent regrowth and to discard the material away from garden areas to avoid spreading any mature seed.
Maintaining healthy, dense turf is a long-term cultural practice that significantly reduces the opportunity for these weeds to establish. Henbit and deadnettle thrive in thin, weak, or disturbed areas, meaning a thick lawn naturally crowds out the space needed for their seeds to germinate. Adjusting mower height to the upper range recommended for the turf species helps shade the soil, reducing the light required for weed seeds to sprout.
In landscape beds, a thick layer of organic mulch can smother emerging seedlings. Applying mulch to a depth of two to three inches creates a physical barrier that suppresses germination. Improving soil drainage and correcting soil compaction through aeration also promotes healthier turf, making the environment less favorable for these moisture-loving annuals.
Effective Herbicide Selection and Application
Chemical control is most successful when treating these winter annuals during the fall or late winter when they are actively growing but still small. Post-emergent herbicide applications made in late spring are significantly less effective because the plants are nearing the end of their life cycle and are already preparing to die naturally from heat stress. The ideal window for application is when temperatures are consistently above 50°F, ensuring the weeds are metabolically active enough to absorb and translocate the herbicide.
For treating henbit and purple deadnettle in established turfgrass, a selective broadleaf herbicide is the appropriate choice, as it targets the weeds without harming the grass. Products containing a combination of active ingredients, often referred to as “three-way herbicides,” are recommended for control. These typically include 2,4-D, dicamba, and mecoprop (MCPP), which together provide a wider spectrum of broadleaf weed control.
When applying any herbicide, follow the label instructions precisely regarding concentration and application rate. Applying on a calm, dry day with temperatures between 60°F and 80°F minimizes drift and maximizes absorption. In non-lawn areas, such as sidewalks, driveways, or bare ground, non-selective herbicides like glyphosate can be used for spot treatment. Non-selective products will kill any vegetation they contact.
Preventing Future Infestations
Since a single henbit plant can produce up to 2,000 seeds, the long-term management strategy focuses heavily on preventing the next generation from germinating. The most common method involves the precise application of pre-emergent herbicides. Pre-emergent products work by forming a chemical barrier in the soil that inhibits the germination of weed seeds.
For winter annuals like henbit and purple deadnettle, the pre-emergent herbicide must be applied in the late summer or early fall, typically when soil temperatures begin to drop below 70°F. Common active ingredients in these products include prodiamine, dithiopyr, or isoxaben. Applying the product before the weed seeds germinate is essential because pre-emergents are ineffective against plants that have already emerged.
Preventing the current infestation from setting seed is a necessary step, which means early removal or treatment before the small purple flowers fully mature. Promoting a thick, healthy lawn remains the best defense against future weeds. Proper fertilization, timely watering, and maintaining the correct mowing height create a dense canopy that physically blocks light and prevents the establishment of new seedlings.