Bamboo can be a blessing and a curse. Whilst bamboo is fast growing and provides excellent screening qualities, its roots (rhizome) can spread giving you and your neighbours a headache.
If you have bamboo and want to keep it or want to use it in your garden, then installing bamboo barrier is a really important consideration.
Do bamboo barriers work?
Simply put, bamboo barriers do work. However, barriers must be correctly specified and installed so that the root barrier can block bamboo rhizome. Here are the four decision factors you need to consider when choosing your bamboo barrier:
- Type of bamboo
There are two types of Bamboo: clumping and spreading (running) bamboo. All bamboos are adventitious, sending out roots laterally if conditions are favourable.
It is our recommendation that both forms of bamboo should be contained by installing Bamboo root barrier. Ideally, bamboo should be completely contained by a continuous barrier. However, as this may not always be possible, in such instances a root barrier system would form part of an ongoing Bamboo Management Plan, which would also employ herbicides and rhizome removal.
Root barriers traditionally have included concrete or metal panels; however, installation of either can be complicated, with concrete prone to cracking if not installed correctly.
Today, most people would look to use a flexible barrier, normally made from polypropylene. When installing bamboo root barrier it’s inevitable that you will be working in tight spaces, this makes flexibility a fundamental factor. Also, the ability to trim the barrier and to be able to thread the root barrier around other obstacles is important.
For a more scientific assessment of plastic root barriers, please see 'Selecting the right barrier' below.
The aim should be to completely contain bamboo by installing Bamboo root barrier. This means that the barrier must go completely around the whole plant. When retro fitting around an existing Bamboo the more space given to the Bamboo the larger it will get. Experience has shown that Bamboo rhizome increases in size year on year and will, over time, put pressure on a root barrier. It is therefore important to give some consideration to this by providing enough space for the bamboo to grow.
Where it is not possible to completely surround the bamboo plant with barrier, it is important to extend the barrier so the end can’t be reached by any laterally spreading rhizome. As we already know, bamboo rhizome is notorious for lateral spread so the length to leave can be difficult to determine. There are many situations where it will not be possible to surround the bamboo; walls and fences are a common culprit. Should this situation arise, bamboo barrier installation should be considered part of an ongoing Bamboo management regime. Other aspects being herbicide control or regular root pruning near to the extremities of the bamboo barrier installation.
Bamboo is essentially shallow rooting when compared to other invasive plants or trees. Often, it only grows in the first 300mm depth of soil. Fundamentally, as an absolute minimum, the depth of a Bamboo root barrier must be 20% greater than the depth of the deepest bamboo rhizome (this should be assessed on a case-by-case basis when digging the root barrier trench, and must be regarded as a very rough guide).
Our experience has shown that bamboo rhizome will root deeper near retaining walls or similar structures. In this situation, and where roots are found at depth, root barrier width and trench excavation depth will need to be adapted so they are both deeper than the rhizomes that the barrier needs to block.
The final depth of the trench can be adapted to meet actual site requirements, however in practice, a root barrier measuring 600mm wide (60cm or 2ft) is commonly needed as a minimum and this allows for trimming and some additional barrier above ground. Again, our experience shows that the actual excavation depth often only needs to be 400-500mm deep (minimum).
One critical part of any bamboo barrier installation is to ensure that the barrier protrudes above ground. Because bamboo roots are effectively stems (rhizomes), they can survive above ground and often travel above ground when seeking new places to grow. Therefore, the barrier must also protrude 100mm or 4 inches above ground to stop bamboo rhizome growing over the barrier.
Finally, it is worth stressing that Bamboo barrier installations do need to be inspected annually. Where there is a need, any rhizome that is trying to work its way over the barrier should be removed. Check the known weaknesses (joints) or the extremities of the barrier that the bamboo could exploit.
What makes a good bamboo membrane?
When deciding upon which flexible plastic root barrier to buy, you may initially think that thickness would be a good indicator of quality. However, puncture resistance is actually more important, since a woven polypropylene barrier will be stronger than a non-woven barrier of the same thickness.
One of the best ways to establish the strength of a barrier is to look at the CBR (California Bearing Ratio) puncture resistance measured in Newtons. Our research suggests that the best quality plastic non-permeable barriers have a CBR puncture resistance of over 5000 Newtons (using the ASTM D6241 test method).
Selecting the right barrier
Selecting the right barrier is clearly important. The size is going to be the first consideration - finding a supplier who can offer a range of sizes is important. Most root barrier distributors provide data sheets which should state the CBR puncture resistance value - this should be greater than 5000 Newtons for non-permeable flexible polypropylene root barrier.
Another important consideration is that you really do need to limit joints in the bamboo barrier. Aim for a continuous barrier with minimal joints. Some barriers interlock or rely on clamping plates, and whilst this may work for other plants but when it comes to bamboo it is not ideal. Where there is a need for joints, these must be carefully welded or taped.
Preparation and digging
Installing Bamboo barrier is a physically demanding task and should only be undertaken by people who are suitably fit enough to see the task through. Further, you need to be sure that when digging you are not going to hit a utility such as electricity. If you are at all unsure about what services may be under the ground, it is best to seek professional advice, or speak to a specialist who can do the work for you.
In summary, the following considerations need to be assessed before installing bamboo root barrier:
keep the area tidy, remove leaf litter, mulch, shingle and weed matting. Put anything you wish to keep to one side. Also, consider sheeting to protect surfaces.
This is ideal for smaller trenches, we would say less than 5 metres. Select the tools to be used for installing the root barrier: trenching spades and crow bars are often needed, particularly if, and when you hit hard ground. In addition, long handled pruners and secateurs will be needed to prune the bamboo rhizome. Bin bags or rubble sacks should then be used to contain rhizome, which will need to be appropriately disposed of.
Hiring a mini or micro digger and qualified driver
These machines are fantastic, but they do require space to operate. As a guide, the smallest ones are about 750mm wide, and some can fit through a standard door.
Consider a professional installation service
Some organisations use soil saws that carve a very thin trench in the ground. This is often seen as a fast and cost-effective solution to trenching. They can also bring everything together, removing the need to buy tools, concerns about digger access and disposing of the waste for you. Our parent company, PBA Solutions offers a root barrier installation service.
How to install bamboo root barrier
A complete 20 point guide to installing bamboo barrier the right way.
- Determine the length you need, appropriately offsetting the barrier from the bamboo. We recommend aiming for 300-500mm off set wherever possible.
- Dig a trial hole to check how easy the digging process is and to assess the depth of the rhizome. This will allow you to determine the depth of barrier needed (see above for more info).
- Find a supplier who has the required depth and length of barrier in stock. Remember, you will need a little more than the estimated length, but don’t be wasteful!
- Place an order for your bamboo root barrier so that it can be with you when you, our your team, are ready to start digging the trench.
- Check the condition of the root barrier when it arrives. Look for any damage that could have been caused during transit. If any damage is found, notify the supplier immediately - do not continue installation.
- Set up the area in preparation for digging the root barrier trenches. Ensure that you have protected areas where soil will be stored and have the correct tools.
- You will need long handled pruners and secateurs to cleanly cut out the bamboo rhizome that you find.
- Chase out any rhizome runners that have spread further than the trenching route.
- Gather all of the waste bamboo rhizome in bags ready to be disposed of, or collected. Be careful to avoid inadvertently spreading fragments of bamboo rhizome around your garden - be methodical as you work.
- Check for sharp objects as you excavate the trench. Remove anything, including any significant stones, likely to puncture the barrier.
- Ensure the trench wall, and any material placed close to a the bamboo root barrier, is free from any such object that could cause a puncture.
- Use additional protection if required. If there is still a concern after removing sharp objects, a protective geomembrane can be used to provide additional protection. This can be applied on both sides of the trench if required.
- Prepare to install the bamboo root barrier by laying it parallel to the trench.
- Before offering the root barrier up to the trench, ensure that any loose soil that may hinder installation is removed.
- Lower the bamboo barrier into the trench carefully - you won't want to come this far only to damage it. Look for any kinks or twists in the barrier, pulling them out as you go so that it is straight and sits on the bamboo side of the trench.
- Make sure that the top of the barrier sits more than 100mm above ground (see above).
- Complete any jointing required by one of two recommended methods. Heat welding will provide the best results. However, this should be carried out by trained and experienced operatives. Alternatively, the root barrier can be tape jointed (on-site if necessary) using a 200mm overlap.
- You are ready to backfill, but do ensure that the barrier is at the correct depth and extends fully along the trench. Keep in mind that as the trench is backfilled, the barrier will be pulled downward. If the barrier extends around sharp corners you may need to introduce some slack to allow for movement.
- Trim the top of the barrier upon completion, ensuring that you leave an above-ground protrusion of at least 100mm.
- Finally, it can be desirable to secure the barrier to a fence or wall. However, we would suggest obtaining advice on this based on the particulars of your project.
Additional points to consideration when planning to install a bamboo root barrier:
- There are commonly two types of root barrier tape available. One is adhesive heavy duty duct tape, and the other is a bitumen type material that has a double sided tacky surface which bonds both pieces of root barrier together. Both work well - the choice is down to user preference.
- When there is a need to either work, weld or joint around services, we recommend obtaining professional specialist advice.
- Please seek further advice from a professional root barrier installation company should you wish to attach root barriers to buildings or structures.
- To complete the Bamboo root barrier installation, unconataminated excavated soil should be carefully returned to the trench compacting in layers.
If you have further questions about installing bamboo root barrier or wish to purchase a Bamboo barrier contact our team, who'll be delighted to help.