We all know that bamboo is well known for its incredible growth rate. In fact, it grows so fast that it may overtake an area, become overcrowded, and block out light. The logical solution is to trim it to the desired size. But, we often worry that cutting bamboo might cause it to spread. Does it?
Cutting bamboo can lead to its spread, but not in the way one might expect. While bamboo doesn’t spread above ground by growing new stalks from the cut, the energy generated when new branches and their leaves form on cut bamboo stalks does promote root growth and colony expansion below ground. Clumping bamboo responds by generating new sprouts within its existing cluster, while running bamboo forms new rhizomes, leading to the enlargement of the bamboo colony from below.
Good news is that bamboo is manageable and easy to contain. By carefully maintaining the roots and planning your garden, you’ll maximize the efficiency of thinning that bamboo grove.
What Happens To Bamboo When You Cut It?
A fully grown bamboo culm (stalk) is thick and tough. When cut, culms will not regrow to their previous height, merely unfurling new leaves at their new height. New leaves equate to increased energy production, which gets funneled back into the roots of the grass for growth.
Bamboo plants undergo a rapid growth phase over 60 days in spring each year. During this time, new shoots emerge from the ground and grow to their full adult height and width. Once these shoots have fully grown, they become segmented rods known as culms, a distinctive feature of bamboo. This entire process takes place within the 60-day growth phase. These culms have a lifespan of around ten years, and as they age, the plant continues to spread, with new shoots emerging and growing into additional culms.
How Does Bamboo Spread?
Despite its appearance resembling a tree, bamboo is grass. Grass roots are close to the surface, extending 2-18 inches belowground. Similarly, it acts as a colony rather than a singular plant, spreading below ground rather than above.
The bamboo plant’s rhizome is the key to its range. Rhizomes are the belowground spreading rootstalk of a plant, the epicenter from which roots, shoots, and nodes form.
The rhizome of bamboo can be categorized into two main types, each responsible for a different growth pattern:
- Running Bamboo: This type has a horizontally growing rhizome that spreads to cover large distances away from the original rootstalk (known scientifically as “leptomorph” rhizomes). New rhizomes form from the spreading roots, assisting in the colony’s expansion as they also form spreading roots. This leads to the aggressive growth that running bamboo is known for.
- Clumping Bamboo: This type of bamboo is non-invasive and has short, dense rhizomes that turn upwards to produce aerial shoots (known scientifically as “pachymorph” rhizomes). New culms (stems) appear next to the existing ones, creating a tightly-packed clump that expands slowly compared to the running types. The rhizome structure grows vertically from the central stalk, forming closely packed shoots above ground. Clumping bamboo is generally considered more manageable and less likely to spread uncontrollably.
These two types of growth behavior help to determine how a particular bamboo species will spread and interact with its surroundings.
Threats Of Invasion
Bamboo’s incredible growth rate and the strength of its culm make it difficult to contain in natural areas with native plants. Clumping bamboo is non-invasive: the root system is closely compacted. Running bamboo can easily turn into forests that overtake our natural flora.
The rhizomes of a running bamboo plant spread fast, and they will only stop when either the extending root is damaged, or the rhizome itself is exhausted. Due to the invasive nature of running bamboo, it can quickly overtake other plants and even structures if not carefully controlled. This threat makes it necessary and often arduous to manage the growth of bamboo.
Controlling Bamboo Growth
Running bamboo will keep spreading like wildfire even when the culms are cut. As new leaves unfurl from the shortened culms, the energy gained assists in further spreading, which in turn results in new rhizome growth.
Bamboo groves are valuable and beautiful; however, thinning a bamboo grove is essential to maintaining an area’s integrity. Controlling the spread of bamboo needs to target the roots, while thinning can occur above and below ground.
Root Pruning
Bamboo roots are easy to prune as they grow close to the surface. For the best results, pruning should occur bi-annually. Those long summer days are ideal for pruning as new shoots would have emerged in spring.
With a sharp spade, cut down into the ground at least two feet from the desired growing area and established culms, cutting off formed and forming rhizomes. You should experience some resistance when breaking through the rhizomes. Next, remove the cut-off segments, and ensure that you remove as much as possible: even the smallest rhizomes can create havoc by creating new sprouts.
Managing Bamboo Growth with Trenches
To maintain an accessible pruning area, dig a trench (12″x12″) around the desired bamboo grow area to stop rhizome spreading. Check the trench for spreading roots annually. You’ll need to make sure that they do not cross the trench. Rhizomes struggle with running over edges or downhill, so they are exposed using this method.
If people frequently walk through the grove or trench area, you might consider filling the trench with loose sand, as it’s easy to dig up if needed. Alternatively, you can use cement to fill the trench or place a large boulder in the space to prevent rhizome growth in that direction. These methods can be effective, but there is another specialized solution for those looking to have more control over the spread of bamboo: bamboo barriers.
Managing Bamboo Growth with Barriers
Bamboo barriers are high-density plastic barriers installed underground to contain the growth of rhizomes. They offer a more permanent and tailored way to manage bamboo, compared to the manual methods like trenches.
Barriers can be open-sided or fully enclosed, providing different levels of containment based on your specific needs.
- Open-sided barriers enclose three-fourths of the bamboo rhizome, directing growth in only one direction. Open-sided barriers may still require pruning but on only one side.
- Fully enclosed barriers stop rhizomes from spreading outside the designated area entirely and do not require root pruning. These are ideal for use in shared garden spaces or when the bamboo threatens to spread outside the bounds of the property.
Culm Thinning
Bamboo can grow to 12 feet high, and groves may become overcrowded with new and old culms. Consider cutting down old culms (6+ years) to increase light penetration into the bamboo grove. Increased light will assist in pest (mites, aphids) control and facilitate better growth for new shoots.
The hard shell of mature bamboo culms can make them especially difficult to cut. Handsaws, machine-operated tools (e.g., chainsaws), and heavy-duty shears are practical tools for thinning. Cut diagonally between the culm nodes (the circular exposed rings on the central stalk), as this approach is often easier with tough stalks. Additionally, wrapping tape around the cutting area beforehand can prevent splintering.
Culm thinning is effective in lessening the aboveground presence of bamboo but does not address the root cause of the plant’s spread. Cutting the culm at ground level may temporarily remove the visible cane, but new shoots can replace it over time. Permanent removal of the plant requires addressing the underlying rhizome system.
Conclusion
Cutting bamboo plants to a more manageable level may feel like an aboveground chore, but it extends much deeper. Potted bamboo and indoor bamboo plants are non-threatening aesthetic arrangements. However, running bamboo found outside is a cause for concern.
Cutting running bamboo culms reinvigorates the roots and leads to the expansion of the colony. The plant’s rhizomes need to be cut away and removed from the soil to curb spreading. Constant vigilance of root growth or artificial intervention is required to stop further spreading.