Halifax is losing its battle against the Japanese knotweed, an invasive species that is crowding out native plants in many areas of the city.

Fallopia japonica, or Japanese knotweed, is a tough, ornamental bamboo-like plant that grows to three metres tall, with a root system as deep as seven metres underground. The weed reproduces rapidly, and can crowd out native species and clog waterways.  

"It's basically in almost every park and right of way in HRM," Richard MacLellan, head of the city's energy and environment office, said.

He admits Japanese knotweed is extremely difficult to get rid of, and there has only been limited success in stopping its spread in areas such as Point Pleasant Park.

"There was a trial of using black tarps. The stuff is very strong, it'll grow right through the tarps," MacLellan said.

The tarps were put on top of the plants in an effort to smother them by cutting off their light supply.

City staff had more success if they walked over the tarp every couple of days, MacLellan said, but cutting the weed back does not work.

"Mowing and mowing and mowing it — in some cases it comes back hardier," MacLellan said.

The fight is already costing tens of thousands of dollars, and he said that bill could grow. 

MacLellan said he thinks regional council should ask the province for help in developing a long-term plan for all invasive species.

In the short term, he said, the city should recruit the Nova Scotia Youth Conservation Corps to help yank out the stubborn weed.

But MacLellan said that even with help, beating the plant back could take years.  

One of largest known stands of knotweed in the Halifax region is on McNab's Island, where nearly an acre is growing unchecked.