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What Is This Purple Flower in My Grass During Winter?

December 21st, 2021

As fall moves out and winter sets in, the weeds we fight in summer either succumb to the elements or go dormant with warm-season turfs. While this may spell demise for these fair-weather foes, their cool-season counterparts are prepared for emergence. Among them is a particularly ugly broadleaf weed known as Henbit.

What Is Henbit?

Purple Flower Winter Weed

Henbit (Lamium amplexicaule) is a winter annual weed that typically germinates in the early fall. In particularly warm winters, it will continue to grow through much of the winter and produce purple flowers when mature. These flowers produce the seed it will germinate from the following fall.

As a member of the mint family, it has characteristic triangular stems that grow either vertically or horizontally. The leaves are opposing pairs, the lower of which have petioles (the small stems on leaves), while higher leaves cup the main stem. Described as triangular and ovate, they often appear round because of the blunt, rounded nature of the cerations on their margins. Against a dormant, tan, winter lawn, the dark green/purple leaves and texture of Henbit are an eyesore.

Cultural Control Practices

As is true with any weed, the best defense for turfs is a good offense. During your lawn’s growing season, this means maintaining fertility, water, and mowing habits consistent with your turf species to optimize health and density. For bermuda and zoysia, we recommend a 1.5-2” cut every 7-10 days and 1” of water per week delivered by irrigation or natural rainfall on 2-3 non-contiguous days. It’s the density and health created by these practices that suppress spring/summer weeds–as well as fall/winter ones.

Special consideration for cultural practices must be made in the fall to ensure that this density isn’t compromised. Damaging turf late in the season as growth slows may mean thinness as weather begins to favor cool weather weeds. Henbit requires light to germinate. Dense lawns that shade the soil surface do a wonderful job of suppressing germination, or limiting the light emerging plants receive.

What Should I Do If I Have Henbit?

A yard that is treated with pre-emergent control products should suppress a majority of the Henbit seed as it emerges. Sometimes, along structures, beds, or margins, mild break-through may occur. Every yard is different and presents unique challenges. Fortunately, henbit is easy to control post-emergence.

As a broadleaf, it is quite different from our turfs, biologically. This means there is a relatively large number of effective control products. While a young plant has a small taproot, its root system is fibrous as it matures. Unlike perennial weeds that store a great deal of energy in tuberous root systems, thin-fibrous roots are more for the harvest of water and nutrients and less for the storage of energy-rich sugars. Generally, a couple of applications of an appropriately labeled post-emergent control product will take care of this blemish. In cold weather conditions, Henbit does slow down its growth dramatically, which will slow symptom expression from an herbicide, but rest-assured, it is controllable.

Important Takeaways

  • Henbit is a winter annual weed with a triangular stem, opposing leaves having rounded/cut margins, dark green/purple foliage, and purple flowers in whorls.
  • Henbit germinates in early fall and continues to grow through warm winters, producing flowers that create seed for the following season.
  • Good cultural practices in the spring, summer, and fall set your lawn up for success as winter weeds attempt emergence.
  • Both pre- and post-emergence products are effective against this weed and will control it but will slow when weather is cold.

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