As you wander through your lawn and garden areas, there are many weeds that already need pulling.

Summer annual weeds die with the first frost. Many perennial and biennial weeds are dormant in the winter.

But you will see many weeds that were emerging all winter, a class of weeds called winter annual weeds.

Among them are common chickweed, deadnettle, henbit, shepherd’s purse and Persian speedwell. But possibly the worst in this group is hairy bittercress. You probably already noticed this weed emerging in the last days of summer.

Hairy bittercress (Cardamine hirsuta) is a member of the mustard family (Brassicaceae). It germinates in the fall and will continue to grow during warm spells throughout the winter. It really picks up growth in early spring. It dies when the weather gets hot in late spring or early summer and after it has dispersed its seeds.

More than one generation can emerge in any given season because its seeds will germinate as long as the environment is moist and cool.

You will find hairy bittercress in your lawn where the turf is thin and in bare areas of your garden beds. Be on the lookout for bittercress in the containers you bring home from the garden center.

This is a small, low-growing weed. The plant develops as a basal rosette, like a dandelion. Two to four pairs of leaflets are arranged alternatively on each leaf stem.

The leaf size ranges from less than one-half inch to one inch, and the terminal leaf (the one at the end of the leaf stem) is the largest. The leaves are round or kidney-shaped.

Thin fibrous flower stems emerge from the center of the rosette and grow from three to nine inches tall. Small white flowers form at the end of the stems. Each flower has four white petals that form in the shape of a cross.

This weed blooms in spring, when cool, moist conditions are present. You can see it in many areas right now.

Hairy bittercress is a prolific seed producer. The seed pod is called a silique and can contain up to 30 seeds.

As it matures, two valves coil within the seed pod. This allows the silique to explode, propelling seeds up to 16 feet. Botanists call this mechanism ballochory, meaning ballistic seed dispersal.

The most important step in eradicating hairy bittercress in your garden is to never let this weed go to seed. As long as the ground is not frozen, it is easy to pull or dig up, fibrous roots and all.

To reduce its numbers, prevent it from germinating by eliminating bare soil in your garden. Mulch your garden beds. Prevent bare spots in your lawn by developing a dense, vigorous turf.

As long as it has not set seed, you can add hairy bittercress to your compost pile.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613.