The invasive plant called Japanese knotweed. Credit: Linda Coan O'Kresik / BDN

Bamboo has a bad reputation in Maine. Many gardeners think of it as an incredibly invasive and aggressive plant. However, much of this is because Mainers mistake Japanese knotweed, an incredibly invasive plant that has damaged many Maine ecosystems, for bamboo.

That’s right: Japanese knotweed is not bamboo.

“Many people call Japanese knotweed (Fallopia japonica) Mexican bamboo or just bamboo,” said Gary Fish, state horticulturist at the Maine Department of Agriculture, Fisheries and Wildlife (DACF). “It is not a grass like true bamboo, but it does have jointed stems like true bamboo.”

But Japanese knotweed and true bamboo are not even in the same family.

“They’re distinctly different plants,” said. “Knotweed is more like buckwheat. Even though it has that type of stem, they’re not even near related.”

The fear is legitimate given the destructive nature of Japanese knotweed, but also misplaced.

“Japanese knotweed is one of the most invasive plants in the world,” Fish said. “It is so easily spread by little fragments in fill soil or on equipment. It causes major problems for many of our streams and rivers because it colonizes the banks and channels the water which speeds up the water causing erosion and flooding. It can also ruin asphalt areas as the growing points are very sharp and tough.”

There are ways you can tell the difference between the two.

“If you can snap the ‘cane’ as you can with Japanese knotweed, then it’s not bamboo,” said Jennifer Estrada, co-owner of New England Bamboo Company in Rockport, Massachusetts.

Bamboo growing in Portland. Credit: Courtesy of Jessica Thurston

However, some bamboos are aggressive. There are two primary types of bamboo: running and clumping. Running bamboos grow using rhizomes, which are horizontal underground portions of the stem that act like roots and allow the plant to spread across the surface of the soil.

“Running bamboos in the Phyllostachys genus like golden bamboo, Spectabilis, Nuda and others are very aggressive,” Fish said. “Their underground rhizomes spread the plants very quickly. I would not suggest that anyone use running bamboos in their yards. It will take over very large areas.”

Think of those troublesome weeds that spread all over your garden and need to be pulled up from the ground in one continuous go — many of those grow using rhizomes, too.

Even these running bamboo species are not technically invasive.

“I would call it more like locally invasive rather than it might take over a bed as opposed to something that’s going to escape and survive in the forest and start displacing native,” Wallhead said. “I would think of it more with its competitiveness along with something like herbaceous perennials that also spread by rhizomes, things like mint or chamomile that can be known to spread but we don’t have forests full of those plants.”

Some Maine gardeners have experience with this weed-like bamboo taking over their gardens and are traumatized by the experience. Others seem open to experimenting with clumping bamboos and have done so successfully.

Jessica Thurston has been growing bamboo in Portland for five years. Thurston grows clumping bamboo without issue, but said her mother has planted running bamboo in the past.

“They have taken over her property completely, and onto neighbors’ properties, and the neighbors hate it,” Thurston said. “Cutting simply does not work. The only safe way to grow running bamboos is in large planters that do not have ground contact.”

Like Thurston, gardeners can select bamboo species that are less aggressive.

“Clumping bamboos [in the] Fargesia species like rufa or nitida will take a much longer time to spread,” Fish said. “Most don’t consider these to be invasive plants as long as they are kept in check in someone’s yard. I suggest that people only consider clumping bamboos. I expect we may end up regulating the running bamboos in the future.”

Wallhead said that when you are selecting a bamboo, elect for one that has been bred to be less aggressive or is known to form clumps.

“Generally the nurseries that propagate or sell bamboo have good descriptions on their sites of the grow characteristics of the bamboo,” Wallhead said.

If you have your heart set on the aesthetics of running bamboo, which is more spaced out than its clumping counterpart, you can also take measures to keep it from spreading, like installing underground barriers to block the rhizomes.

“The only way to prevent them from invading almost any open area is with a very heavy plastic barrier that is 30 inches deep and about two inches above ground,” Fish said.

Or, running bamboos can be grown in containers.

“Containers are great for bamboo because you can obviously manage to grow if the container is sitting on the soil,” Wallhead said. “If you see plants growing around the base, they can be pretty easily removed.”