Mexican bamboo can grow up to 9 feet in height with leaves 6 inches long.
Mexican bamboo (Polygonum cuspidatum) is not a true bamboo but rather a large, robust member of the buckwheat family. It is also called Japanese knotweed.
Mexican bamboo grows very rapidly, with heights ranging from three to nine feet. Its slightly zig-zag stems are hollow, with large triangular-shaped leaves appearing singly. Greenish-white flowers with five petals appear in clusters that resemble thin drooping white lilacs.
The characteristic that makes these plants so tough to eradicate is their persistent underground fleshy rhizome (stem), growing five feet or more out from the upright stems.
Dig out as much of this rhizome system as possible. When new shoots reappear, dig those up too, or use glyphosate (Monsanto Roundup) directly on their leaves. Eventually you will kill the plants, but it might take years of work. Any time you allow them to grow actively and increase in leaf area, additional energy will be stored in the roots and rhizomes, making the job more difficult.
Glyphosate must be sprayed or wiped onto the leaves carefully as it is a non-selective herbicide and will kill or damage most green, living plant tissue it contacts. Glyphosate works only through the foliage or green stem and so should not be soaked into the soil. Apply it in autumn, before the foliage turns color. Repeat applications are usually needed on Mexican bamboo, perhaps for several autumns in a row. As with all pesticides, read and follow label directions carefully.