Controlling Bamboo Spread
Having a bit of knowledge of rhizome characteristics will allow one to apply the best method for controlling bamboo spread.
Bamboo is a very shallow rooted plant. Bamboo rhizomes typically grow within the first 6" below the surface of the ground. The rhizomes produce feeder roots that grow further down into the soil. Typically the roots don't grow anymore than 20" (50cm) below the surface of the ground. For most bamboos, rhizome development and growth takes place late summer to early fall.
Bamboo rhizomes grow in two unique characteristics. They either grow in a clumping formation or they can grow in running habit. All species of bamboo are classified either as a clumping bamboo or a running bamboo.
To learn more about bamboo, see Bamboo Growth Habits.
Clumping bamboos have Pachymorph rhizomes that grow upwards developing into a new culm. New rhizomes emerge from buds on an existing rhizome and so forth. This accumulative effect causes the grove to expand slowly around the perimeter. This growth behaviour gives the bamboo a 'clumping' habit and new growth is predictable and easier to maintain. Because of the predictable growth pattern, containment may not be necessary. However, proper maintenance should still be followed.
Running bamboos have Leptomorph rhizomes that run horizontally under the ground. New buds and roots emerge from the nodes of the rhizomes. Most buds remain dormant but may develop into a new culm or it may develop into another new rhizome. Any new rhizomes will also run horizontally underground and produce more news culms and rhizomes. This growth behavior gives the bamboo a 'running' habit.
Running bamboos with Leptomorph rhizomes typically require methods to control their spreading habit.
Bamboo Shoot Removal
The majority of bamboos shoot in spring or early summer. If a shoot emerges in an area where a culm is not desired,it can removed by severing it at ground level. Bamboo shoots are very soft and tender and can broken off effortlessly by simply kicking it or twisting it off by hand.
This method of control is not very effective as it only controls where you don't want a culm to grow. The rhizomes underground will simply continue to grow and send out shoots again the following year. A better approach is to prune the rhizomes.
Bamboo Rhizome Pruning
Pruning the rhizomes is a fairly simple task which involves severing the rhizomes within this growing area. Pruning rhizomes on a regular basis is the most effective solution for controlling bamboo spread.
The best tool for the job is a sharp, flat bottomed garden spade. It involves just plunging the spade into the soil, severing any rhizomes. You would repeat this around the whole perimeter of your bamboo grove. The severed rhizomes outside the perimeter can then be pulled from the ground. Rhizome growth generally ceases between late fall and early spring. During this period, new rhizomes are somewhat tender and makes pruning easier.
Large, older, well established bamboo groves can be a bit more tedious when it comes to pruning the rhizomes. The rhizomes are thicker and generally harder. Severing them with a garden spade involves a lot more force and effort. In the extreme cases, saws or tree pruners may need to be used.
This method involves growing the bamboo above the surface ground level. A mound of soil 12" (30cm) high is created. The bamboo is then planted anywhere within that raised bed. The area of the raised bed is of course dependant on how much space you have. Any new rhizome growth will most likely be spotted growing down the bed, which can then be pruned.
This method is probably the least labour intensive as there is no digging required or removing any obstacles (ie. Boulders, tree roots, etc.). It also has a few major advantages. Because the growing area is above grade, there is less possibility of the soil getting water logged. The water just simple drains downwards into the area below the raised bed.
Creating a raised bed also increases the surface area, allowing more oxygen to circulate through the soil. The combination of more oxygen and well drained soil is more beneficial as opposed to bamboo in flat ground.
However, because the raised bed is above ground, it is exposed to more rain and wind. This can potentially cause the soil to erode more quickly if not protected. It is recommended to mulch the raised bed to prevent soil erosion.
Trenching involves digging a trench roughly 12" (30cm) deep by 12" (30cm) wide around the perimeter of the bamboo grove. Any new rhizome growth can be seen attempting to cross the trench. The rhizome can then be pruned and removed.
Depending on the soil type, the trench may retain water forming a muddy puddle. Also, having a trench may not be the most visually appealling. Loose material such as wood mulch or sand can also be used to fill the trench if desired. In this case, visually spotting the rhizomes may be more challenging. Detecting rhizomes can be as simple as dragging a tool such as a pick through the trench. Any new rhizomes will most likely snag onto the pick as you drag across it. Once detected, the rhizome can be pruned.
Bamboo barrier is a long stretch of barrier that surrounds the perimeter of the bamboo grove. Any bamboo rhizomes that grow into it will be deflected and contained in the surrounding perimeter. Bamboo Barrier can be made from concrete, metal or plastic sheets.
This method of bamboo control is the most laborious but the biggest advantage is that it offers the least amount of maintenance work, at least for a few years. However, a bamboo barrier is much like a very large container. Over the course of many years (depending on the size of the enclosed barrier), the bamboo grove will eventually become root bound. Eventually, the rhizomes can build up an enormous amount of pressure and cause the barrier to fail.
HDPE (high density polyethylene) sheets are most commonly used for bamboo barrier. It is light, flexible and easier to install than concrete and metal. Most notably, it does not corrode, crack or deteriorate. It comes in rolls of varying thicknesses and widths. Most often they are available in rolls of substantial lengths so it can accommodate even the largest of projects.
Installing barrier involves digging a deep trench around the perimeter of the bamboo grove. The barrier is then placed vertically in the trench surrounding the bamboo grove.
The top of the barrier should extend 2 inches (5cm) above the ground to create a lip. This will prevent any rhizomes from leaping over the barrier. Even if they do, they will be easily spotted and can be pruned off. The lip also serves as containment for mulch and leaf debris.
If the perimeter is to be fully enclosed with plastic bamboo barrier, it is recommended to clamp and bolt the two ends together.
Combination: Raised Bed With Bamboo Barrier
Applying any combination of the above methods together can also be very effective depending on the situation. A common method is to grow the bamboo on a raised bed and installing a bamboo barrier on one side only.
The bamboo barrier prevents spread on one side. The other side allows the rhizomes to grow freely without getting root bound. Any rhizomes that attempt to escape on the open side can easily be spotted running down the raised bed. These rhizomes can then be pruned.