Unmask weedy intruders during the cool season

I only pay close attention to weeds once the spring gardening season begins and I start to work outside. Seeing plants that I know I didn't plant, I wonder who these intruders are.

Cool season weeds fit the very definition of a weed: any plant you don't want in your garden. Cool season weeds, or "annual winter weeds," germinate in the fall and set seed in the spring, the opposite of warm season annual weeds that germinate in the spring and set seed in the fall. During fall's cooler days, this new generation of weed seeds germinates, putting on an initial top growth that continues through late winter/early spring, depending on the temperature. In spring's warmer days, they produce leaves and flowers and with summer's heat, they die.

Four common annual winter weeds are:

Henbit and Purple dead nettle: Easily confused, these two members of the mint family have square stems and opposite leaves and tubelike pink or purple flowers March to May. When young, the stems lie on the ground and have upwardly rising tips; older plants grow upright. The difference is their leaf shapes: henbit has round leaves and edges with rounded teeth; dead nettle has deeply lobed, triangular leaves with purple or red upper leaves.

Bittercress: A member of the mustard family, bittercress has erect, smooth, branched stems growing from a central point. Each stem has pinnate leaves with round or wedge-shaped ladderlike leaflets. The plant's four cross-shaped white petals provide its name: cress is Latin for "crux." Be careful when removing this plant: if touched when ripe, the seed pods spring open, causing the seeds to fly out. In England, it is known as "popping cress!"

Annual bluegrass: This weed has boat-shaped leaf tips and pale green color, grows upright reaching up to 12 inches and producing up to 100 seeds in an eight-week period. In the fall when soil temperatures drop below 70 degrees, the seeds germinate.

Chickweed: Chickweed has small, bright green oval leaves with pointed tips. Stems are 3 inches to 15 inches long, limp or slightly erect, and branched. Preferring shady, moist locations, it forms a thick springy mat and forms roots where the nodes touch the soil.

If you were surprised this spring by these weeds, remember they are prolific and seeds can remain in your soil for years. Keep a watchful eye and a trowel in hand - and you can reclaim your garden turf!

- Arlene Swartzman

• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines. Call (847) 298-3502 or email northcookmg@gmail.com.