Pruning vs thinning
Bamboo needs less pruning than most shrubs, but a little regular attention keeps it healthy and good-looking. Two jobs are involved:
- Thinning removes whole canes at ground level to open up the clump and let in light and air.
- Pruning or trimming shortens canes or removes side branches to control height or shape.
Bamboo is a giant grass, so it tolerates cutting well. The important rule is that a cane, once cut, will not grow taller from the cut point. New height comes from new shoots each growing season. This differs from deciduous ornamental grasses, which are cut back to near the ground each year.
What you can safely cut
- Dead, weak, damaged or broken canes, cut as close to the ground as you can.
- Old canes that look tired or scruffy. Canes can live for many years, but older ones carry less attractive foliage.
- Side branches that are dead or in the way.
- Unwanted new shoots, while they are young.
Make cuts just above a node (one of the rings on the cane). Cutting between nodes can leave a hollow stub that dies back and looks unsightly.
Thinning a clump step by step
- Stand back and look at the clump. Identify old, dull, damaged or crossing canes.
- Cut chosen canes to the ground with loppers or a pruning saw. A common rule of thumb is to remove roughly a quarter of the growth each year, focusing on the oldest canes, though you can thin more or less depending on how dense you want the clump.
- Leave a mix of ages so the clump always has canes in leaf and a supply of strong new growth.
- Remove the cut canes. They can be saved and dried for garden stakes, or chipped for mulch.
Bamboo that is never thinned becomes crowded and may produce thinner, leaning canes. If you are growing bamboo in a pot, thinning also helps keep the plant manageable. See growing bamboo in pots and containers.
Trimming height
If a bamboo is taller than you want, you can top it.
- Cut canes just above a node at the height you want.
- Expect the cut canes to stay at that height. They will not regrow taller, and the plant often gets bushier below the cut.
- For smaller screening bamboos with flexible canes, you can sometimes bend a cane down, cut it, and let it spring back up, which avoids using a ladder.
- Keep some side branches on each cane. Without branches, the cane may die back.
- Consider that some large species look best at their natural height and shape. Topping a tall timber bamboo can look awkward, so choosing a smaller species at planting time is often better.
Because a topped cane will not grow, plants trimmed this way can look flat-topped until new, taller canes replace them. New shoots from ground level will still come each spring and may grow taller than the cut canes, which is how the clump refreshes.
Removing lower branches
A popular look is to clear foliage and side branches from the lower part of the canes so that their colour and shape show. A commonly suggested proportion is to clean about the lower third and leave the upper two-thirds bushy. This also lets light and air reach the base.
Take care not to over-prune if privacy is the goal. A screen with bare lower canes lets people see through. If you need density at fence height, remove less. For screening tips, see planting a bamboo privacy screen. Removed branches usually do not grow back strongly, so cut conservatively.
Keeping clump size in check
Clumping bamboo widens slowly as new shoots come up around the outside.
- Remove new shoots at soil level while they are soft, before they harden into canes. They can often be snapped off or cut with pruners.
- Cut back outer canes to ground level if the clump is getting too wide.
- Avoid pulling shoots out from the roots, which can damage the plant.
Running bamboo is a different job. If it spreads by rhizomes, pruning canes will not stop it. Read how to control and remove bamboo and how to install a rhizome barrier.
Groundcover bamboo
Low-growing running bamboos (up to about 5 feet) can look ragged. A common approach is to cut them back hard, by mower or shears, at the end of winter before new growth starts, much as with mondo grass. This renews the foliage and keeps the plants shorter and denser.
When to prune
- Thinning and removing old canes: can be done at most times of year. Many gardeners do it in late summer, fall or late winter.
- Topping: late summer or fall is often suggested. Avoid cutting during the spring shoot flush, when the new canes are soft and vulnerable.
- Removing unwanted shoots: as they emerge in spring, since they are easiest to snap off while soft.
- Hard cut-back of groundcover types: late winter, before the new growth.
Tools and safety
- Sharp bypass loppers or a pruning saw for canes.
- Hand pruners for branches.
- Gloves and eye protection. Cut canes can splinter into thin, sharp slivers.
- Cut thick canes with a saw rather than loppers to reduce splintering.
Lucky bamboo is different
People also search for how to trim an “indoor bamboo plant”. Most of these are lucky bamboo (Dracaena sanderiana), which is not a true bamboo. It is trimmed differently, and you can cut a stalk to shorten it, but the plant grows new foliage from beneath the cut, not new canes from soil. The advice in this article applies to true garden bamboo.