Extension Educator, Horticulture
For most people the weed wars start in summer. Some weeds, however, come in under the radar and are blooming now long before we get out our arsenal. These early bloomers are called winter annuals. Their seeds germinate in the fall then flower in early spring of the next year to form many, many seeds.
These weeds are probably lurking in your garden right now. Winter annuals appear in disturbed soil areas from tilling, where the dog dug and where the kids make shortcuts through the lawn.
Henbit is a common early season weed in lawns, landscapes and gardens. Henbit, Lamium amplexicaule, is often confused with creeping Charlie, Glechoma hederacea. Both have square stems and are in the mint family. Both have lavender to blue tubular flowers. Henbit flowers tend to be more on the purple/lavender range whereas creeping Charlie flowers tend to be more in the blue range. Henbit flowers are clustered at stem tips with clasping leaves (like lacy collars) below the flower cluster. Creeping Charlie does not have the clasping leaves. Both plants have round shaped, scalloped leaves.
The life cycle and flowering time and therefore control measures differ with henbit and creeping Charlie. Henbit is a winter annual and creeping Charlie is a perennial. The original creeping Charlie plants come back every year accompanied by many seedlings. Henbit has to start from seed each year. The henbit plants that are blooming now germinated last fall. Henbit as a winter annual blooms very early in the spring, well before creeping Charlie blooms. Henbit is blooming right now in east central Illinois. Around here you will often see whole farm fields of henbit in bloom early in the season. Forgetting the weedy aspects of the plant, it really is quite pretty.
Controlling seed production is the key to controlling annual weeds. Early bloomers need to be removed now before they set seed. Luckily most have very small root systems and are easy to pull or hoe. In gardens many weeds can be smothered with thick layers of wet newspapers topped with several inches of compost or mulch. In lawns maintain proper lawn density to eliminate open areas for weeds to develop.
It is too late to use pre-emergent and probably too late to use post-emergent broadleaf herbicides to control winter annuals. To be effective on annual weeds pre-emergents have to be used before the seeds germinate and post-emergents have to be used while the weed is actively growing and before the weed flowers. Pre-emergent herbicides could be used in late summer to control winter annuals before they germinate. Corn gluten sold as Concern, WOW and others is labeled as an organic pre-emergent control of some weed seeds such as lambsquarter, crabgrass, purslane and velvetleaf. It must be applied 3-5 weeks before weeds emerge, in other words – now to control summer weeds and again in late summer for winter annual control. Check out the Iowa State University website at www.gluten.iastate.edu for more details.
Success in controlling perennial weeds such as creeping Charlie is in controlling the original plant through hoeing, hand removal or herbicides and in controlling seed production. Despite what you may hear, borax is not labeled for use as an herbicide to control creeping Charlie. At present there is no research to document its efficacy or lack of harm. Herbicides containing 2,4-D; 2,4-DP; clopyralid; dicamba; MCPA; MCPP or triclopyr alone or in combination can be used to control creeping Charlie. Be sure to read and follow all label directions on any pesticide.
With any weed control, accurate identification is important. Check your local library for weed identification books or bring samples to your local U of I Extension office.