Extension Educator, Horticulture
If you are brave enough to venture into the limp, brown, cold-burned world of your vegetable garden you may be surprised to see luxuriant bright green leaves of a few seemingly confused plants. We typically think seeds germinate only in the spring. However some seeds purposefully germinate in the fall. These plants are commonly called winter annuals. The young plants are very cold hardy and often stay green late in the season. The same plants then flower in early spring and form seeds well before we have located our garden boots.
Winter annuals will germinate in bare soil areas and where the soil has been disturbed through garden tilling, dog digging, or kid running in lawns, gardens, and fields.
A common winter annual, Henbit (Lamium amplexicaule) is often confused with Creeping Charlie, Glechoma hederacea. Both have square stems and are in the mint family with small tubular flowers. Henbit flowers are more in the purple/lavender color range and are clustered at stem tips with clasping leaves below the flower cluster. Creeping Charlie flowers are more in the blue range without the clasping leaves. Both plants have round shaped, scalloped leaves and are often considered weeds.
A couple differences between Henbit and Creeping Charlie include the life span and flowering time and therefore control measures. Henbit is a winter annual and Creeping Charlie is a perennial. The original Creeping Charlie plants come back every year. Henbit has to start from seed each year. Henbit as a winter annual blooms very early in the spring and well before Creeping Charlie blooms. Around here you will often see whole farm fields of purple flowered Henbit early in the season.
Common Chickweed, Stellaria media, is another winter annual. It is a low spreading plant that can grow 4-12 inches tall. It often grows in the shade of trees and shrubs or the north side of buildings. Chickweed has light green, small and ovate shaped leaves with pointed tips. The flowers are small, white with five deeply notched petals. The stems are creeping and often root at the leaf nodes.
Another group of winter annuals are the Speedwells, Veronica spp.. Corn Speedwell, Veronica arvensis, commonly grows here and may be flowering right now. Seeds may also germinate in early spring. The leaves are small with scalloped edges. The flowers are blue with a white center.
Shepherdspurse, Capsella bursa-pastoris, plants may be abundant now as deeply lobed leaves in flat rosettes. It blooms in very early spring. The small white flowers appear on 6-8 inch stalks. The flowers develop into triangular shaped seedpods.
For foragers winter annuals are a tasty treat since they are green when little else is. Chickweed salad comes to mind. Whether your goal is slathering with butter or slaughtering with a hoe, accurate plant identification is crucial. Check your library for weed identification books or bring samples to your local U of I Extension office.
Control of winter annual weeds includes removing plants now by hoeing or hand pulling. Broadleaf herbicides can also be effective if used while the weed is actively growing now or before the weed flowers in early spring. Realize herbicides are not effective at cold temperatures. Be sure to read and follow all label directions.
Once annuals flower and form seeds, controlling the original plants does nothing for future control but does provide some relief from revenge issues. Beat 'em or eat 'em winter annuals are green and growing when other plants are dead and decomposing.