Plants that conveniently fill out an ornamental garden can cause big headaches down the line, in part because of what makes them so successful at growing in your yard.
One of those plants that could take over your garden is Bishop’s Weed, also known as goutweed or ground elder. The low-lying, quick-spreading plant widespread throughout Maine was sold by nurseries as a ground cover for years before it was classified as severely invasive.
Maine implemented a Do Not Sell list in 2018 outlawing the sale of certain plants including Bishop’s Weed. The list was expanded again in January. But the legacy of previous years remains in many gardens and yards; fragments of plants also travel in potting soil or seedlings, meaning there’s reason to keep vigilant.
Nursery plants are a leading source of invasive species spreading. Sometimes soil in noninvasive species contains other plants; that’s how the invasive mile-a-minute weed likely made it to Maine last summer.
Bishop’s Weed in particular can withstand tough conditions and spreads primarily through rhizomes — a shallow network of connected roots — under the soil, rather than seeds. This makes it quick to grow, eager to crowd out other species and difficult to remove.
The rhizomes can even work their way through the roots of other plants in your garden. Tiny fragments start a new patch, meaning it can end up in your garden from outside soil or from parts that snap off while you’re weeding.
You can make a dent in its population by hand, but it takes time and patience.
“It’s a war, not a battle,” said Kate Garland, a horticulturist with the University of Maine Cooperative Extension.
She has been dealing with a well-established patch of the weed at a university demonstration garden. She started with a “big dig,” removing roots on an overcast day shortly after it rained so that the plants she wanted to keep would be less stressed by the change.
Perennial plants in the area can be moved to pots while you work on removing the weed, which might take several years.
Garland removed fragments of the Bishop’s Weed roots from the desirable plants, which the recent rain helped her do. In dry soil, the roots will often snap off when pulled. You can also loosen the soil with a garden fork, being careful not to break the roots below.
Then, you can mow over the area on a low setting for several weeks before covering the site with cardboard and a layer of mulch to kill future growth.
She revisited it several more times over a few weeks, and recommends keeping weekly vigilance on any area where you’ve removed it.
It isn’t just a pain to get out of your garden. Scientists have found that its rhizomes change soil chemistry and disrupt ecological functions including decomposition and nutrient cycling in woodlands.
In wooded areas, it could make it more difficult for tree species to grow.
It’s in the carrot family, related to other common garden sights such as Queen Anne’s Lace and the toxic Giant Hogweed, a tall plant with a similar structure that can cause burns and even blindness. It has a familiar structure and either solid green or variegated green-and-white leaves on stems growing one to two feet tall.
Bishop’s weed may also irritate some people’s skin. But others eat the leaves, which are reportedly comparable to spinach when harvested young, before they’ve fully unfurled. The leaves can look similar to other, less edible groundcovers, though, so make sure you’ve identified it clearly.
Websites like iNaturalist have lots of photos and identification information for the plant.
