Japanese Knotweed Looks Pretty, But it's Pretty Aggressive, Too

It may look pretty, but it could cost you. Japanese knotwood is blooming right now, and it's tougher than its creamy white flowers would indicate. It can grow up through sidewalks, driveways and foundations. In addition to the multitude of tiny flowers clustered in spikes at the top of the plant, look for broad leaves climbing in a zigzag pattern up a hollow, bamboo-like stem. It can grow up to 10 feet in height, and its root system can crawl along underground for more than 60 feet.

"We've seen places the size of a football field, the size of a tennis court, where nothing else grows besides Japanese knotweed. So, it's wreaking havoc on the environment," said Sue Tangora with the Michigan Department of Natural Resources (DNR). And it's mean! The DNR says it has the ability to choke out competing plants by emitting toxic chemicals.

It's illegal to bring the plant into Michigan, according to the Detroit Free Press.

"When you cut it down and try to kill it this year, you haven't killed it; there's the rest underground and it will be coming up again," Susan Julian, a land specialist with the North Oakland Headwaters Land Conservancy, told the Free Press.

The plant first came to this continent as an ornamental plant. It was popular because it grows quickly and its attractive flowers are good pollinators. It quickly outwore its welcome.

"It's very tenacious, very hard to kill," Tangora said. "It can grow through your foundation, your sidewalks. I've had calls from people who had their driveway done two years ago, they had soil brought in and, boom, Japanese knotweed grew up through their driveway."

Now, "the horse is out of the barn" for the plant's spread as an invasive species, she said.

"We're finding it in hundreds of sites throughout Michigan," she said. "Once you get an eye for it, you'll start seeing it everywhere." And now is the time to eradicate it, before it goes dormant for the winter.

Photo via Michigan DNR.