invasive weeds

Weed of the Week: Bittercress

While most other plants are just awakening from winter hibernation, Bittercress (Cardamine hirsuta) is actively growing and blooming.  It is an annual weed in the mustard family. It reseeds itself so rapidly that it appears to be perennial. The plant forms a basal rosette of lobed leaves and sends up a wiry stalk. The 4-petal white flowers have a lavender tint near the base. The flowers can mature and set seed in less than a week. Once a few plants have seeded, it is almost impossible to eradicate from the lawn or flower beds.

Pulling the weeds while they are small, before they set seed, is the best way to control this invasive demon. They are easy to remove when soil is damp. If you allow them to seed, you will need to employ both pre-emergent and post-emergent herbicides (look for product that controls broadleaf weeds) to tame it.

Even a tiny plant can bloom. See the photo below, with a house key to show size of the blooming plant. The seed pods, called siliques, look like purple toothpicks. The pods will explode at the slightest touch, throwing seed up to 15 feet away from the mother plant. One of its common names is Shotweed. There is a term for this ballistic seed distribution system: ballochory. Touch-me-nots (Impatiens balsamina) also throw their seeds around this way.

In a Master Gardener class I attended some years ago, the instructor showed a photograph of a nursery in which one Bittercress was left alone for nine weeks. It went from a single plant to an entire village. That one plant spread its progeny to the surrounding twenty-four flats of plants — in just nine weeks!

Bittercress leaves are edible. I’m told they taste like arugula. They do support several varieties of butterflies and one obscure bee, but they are also favored by aphids. In the Mary Snoddy garden, this means “Off with their heads!”

Weed early and weed often.

A single, tiny bloom produces a bazillion seeds, all of which will germinate.

A single, tiny bloom produces a bazillion seeds, all of which will germinate.