Volunteers at Broad Branch are battling invasive garlic mustard – to give native plants a fighting chance

A team of volunteers has been clearing bamboo at Broad Branch Stream. That’s not the only invasive species they are battling. John Burwell of the Pinehurst Project tells us what’s on their radar now:

This is Tucker Harris, of Ingleside at Rock Creek Park.

Volunteer Tucker Harris at work. Note the plastic bag she’s using to contain the plants she’s removing from Broad Branch Stream. (photos courtesy of John Burwell)

She has been part of the Pinehurst Project volunteer effort at Broad Branch. She’s been busy removing English ivy from trees, but now that spring is here, removing garlic mustard (Alliaria petiolata) is more important.

Garlic mustard, a Class A noxious weed, is a biennial or winter annual herb that generally grows two to three feet in height, and sometimes as tall as six feet. It is allelopathic, producing chemicals that inhibit the growth of other plants and mycorrhizal fungi needed for healthy tree growth and tree seedling survival. Garlic mustard is a threat to the diversity of many native ecosystems. Invasions have a very dramatic impact on the ground layer flora, strongly reducing abundance of native plants, more from this chemical warfare than from direct competition.

This plant gains a foothold in fields and forests by emerging earlier in spring than many native plants. By the time native species are ready to grow, garlic mustard has blocked their sunlight and outcompeted them for moisture and vital nutrients.

Garlic mustard is in the Broad Branch forest, where Nevada Avenue/Broad Branch Road meet Linnean Avenue.

Removal efforts need to be continued for several years to eliminate the seed bank, those seeds that remain in the soil. They may not germinate until conditions are ideal. Plants must be pulled, bagged and disposed of to prevent further seed dispersal.

These garlic mustard seedlings will grow to produce flowers and seeds next spring. We will endeavor to rid the area of these seedlings to limit the quantity of plants we’ll need to pull next year.

Garlic mustard was introduced to North America by European settlers in the 1800s who used the herb for culinary and medicinal purposes, and as the name suggests, it has a garlic-like smell and a mustard-like taste. On average, a garlic mustard plant will produce 22 siliques (seed pods), each of which can contain as many as 28 seeds. A particularly vigorous plant may produce as many as 7,900 seeds, although the average is more likely to be in the 600-seed range. The seeds generally germinate within one to two years, but may remain viable for up to five years in the seed bank. Seed dispersal is mainly by humans or wildlife.

English ivy does remain a threat. It must be removed as the stress from the added weight of rain, snow, ice and wind resistance can be a contributing factor in toppling trees. And you can help the volunteers eradicate both English ivy and garlic mustard by taking note of what is growing in your yard. Rock Creek Conservancy asks residents to take the ivy pledge and remove the plants from their properties.

To join the volunteer efforts at Broad Branch Stream, contact John Burwell at [email protected].