Bamboo Species Identification: Running or Clumping, and Which One

Running versus clumping, and how to tell

Running bamboos have leptomorph rhizomes — long, thin, vigorous underground stems that travel metres per year and send up culms at intervals along their length. The result is a spreading thicket that keeps going. Phyllostachys, Pleioblastus, Sasa and Pseudosasa all run.

Clumping bamboos have pachymorph rhizomes, which are short and thick and turn upward to form a new culm close to the last one. The clump expands slowly outward. Fargesia, Bambusa and Chusquea clump.

In the ground, the difference is visible. A running bamboo shows widely spaced, separate culms in a loose patch. A clumping bamboo shows a tight, dense cluster of culms all arising from roughly one point.

If you only have a photo of leaves, you cannot tell. That is worth saying plainly rather than guessing — the answer changes the advice completely.

The main genera

Reading the culms

• The node. Bamboo culms are jointed, with a solid ring at each node. Phyllostachys species often have a distinctive white band immediately below each node, which is a strong identifier.
• The internode. Some Phyllostachys have a flattened or grooved side on each internode, alternating up the culm. Run your hand up the stem and you can feel it.
• The colour. Culms range from green through yellow, black, red and striped. Phyllostachys nigra is black. Phyllostachys aurea is yellow-green and often has compressed lower internodes.
• The sheath. Culm sheaths wrap the new shoots in spring and are highly diagnostic for Phyllostachys, but they are only present for a few weeks.
• The diameter. Very thin culms at close spacing suggest a ground-cover Pleioblastus. Thick culms suggest Phyllostachys or Bambusa.
• Hollowness. Most bamboo culms are hollow. Chusquea culms are solid, which is genuinely unusual and easy to check.

If it runs, this is what containment takes

Root pruning does not work. This is the thing people try first and it fails, because the rhizomes travel deeper and faster than you can dig.

The only reliable method is a rigid physical barrier. It needs to be at least sixty centimetres deep, ideally more, and made of high-density polyethylene or concrete rather than pond liner. It must be installed around the entire root zone, with no gaps at the corners and the top edge standing five to eight centimetres above soil level so rhizomes cannot hop over.

Angling the top of the barrier slightly outward helps, because rhizomes that reach it tend to turn upward and can then be cut off.

The alternative is a large container. A running bamboo in a sturdy pot, with the pot standing clear of the ground rather than sunk into it, is genuinely contained. Sinking the pot achieves nothing, because the rhizomes escape through the drainage holes.

If you inherit a running bamboo you do not want, cutting the culms does not kill it. You need to dig out the rhizome mass, and even then it will regrow from fragments. It takes years, and it is the reason so many people give up and move house.

The non-bamboo lookalikes

Two plants get mistaken for bamboo, and both matter.

Japanese knotweed has hollow, jointed, bamboo-like stems and grows in dense canes. But its leaves are alternate and broad with a heart-shaped base, it has no culm sheaths, and the stems are red-speckled when young. It is a serious invasive plant and a legal problem in many countries, so misidentifying it is worth avoiding.

Horsetail has jointed stems that pull apart like a telescope, which feels very bamboo-like. But it has no true leaves, it is much smaller, and it is a primitive plant rather than a grass. It is also extremely difficult to eradicate once established.

The difference in all cases comes down to the sheath and the leaf. Bamboo has culm sheaths and true grass blades. Neither lookalike does.

I have watched a neighbour spend three summers digging bamboo out of a border it was planted in during the nineties. It is still coming up. The original planting was a single pot, and nobody at the garden centre mentioned that it ran.

That is the whole problem with bamboo. The species name is interesting. Whether it runs or clumps is the only thing that actually matters, and it is the one thing that does not appear on the label.

So this page puts the running-versus-clumping answer first, because it decides whether you have a feature or a decade-long problem.