When creating a hardscape - sidewalks and infrastructure carefully designed for function and/or aesthetics - the last thing you want is to see it all destroyed. Or even if not destroyed, it’s no fun to see all your hard work compromised at all.
Surrounding and supplementing this hardscape is often landscape that is “living”—grass, bushes, plants, flowers and very frequently, trees. And while these live elements no doubt add color and beauty, they can also be challenging because their growth is dynamic - changing - and somewhat hard to control. Thus, the hardscape must account for those factors in advance.
A Deep Root Barrier Helps to Preserve Your Hardscape
One of the most challenging of the challenging aspects are trees that are integrated into the hardscape design. Primarily, because trees have large root systems that as they grow, can lift up or disrupt sidewalk and curb design or even invade other parts of the infrastructure such as irrigation and lighting systems. They can also break through and uproot your carefully-designed landscape elements as well.
Unfortunately, there is little that can be done to totally eliminate this problem or especially, risk. On the other hand, there are solutions that - with strategic pre-planning - can dramatically reduce the risk of damage to your hardscape and infrastructure from unwieldy and uncontrolled tree root growth.
How Does a Tree Root Barrier Work? Does It Harm the Tree?
Deep root barriers for trees work by controlling the direction of tree root growth in such a way that the potential for those roots breaking through sidewalks or encircling and/or destroying other infrastructure or landscape elements, is dramatically reduced.
There are 3 primary types of tree root barriers:
- Root Traps or Screens
Root traps and screens are usually welded fiber sheets or woven fabrics that allow the roots to penetrate but retain and redirect them to a degree.
- Root Deflectors
Root deflectors are made of plastic or metal. These types of barriers are typically most effective if they are at least .15mm. Their goal is to create a physical barrier that will contain the tree root growth fairly completely and direct it downward, deep enough so that when and where growth occurs, it is not disruptive.
- Chemical Inhibitors
This type of deep root barrier is akin to root traps or screens but with an added chemical component—frequently Cupric Carbonate (CuCO3). Another common chemical used in chemical inhibitor root barriers is Trifluralin—a herbicide that slows root tip growth. Obviously, the chemicals will break down over time, reducing effectiveness long-term.
Of course, one concern of many people is whether this root “manipulation” harms the tree itself in any way.
Obviously, if improper or poorly designed root barriers are used - or if any deep root barrier is not installed right - a tree’s root system cannot or will not grow properly. Thus, the tree itself could be compromised.
Alternately, most experts contend that if a good root barrier is chosen and is installed properly, root barriers do not harm trees. In fact, they may protect the tree by allowing the tree to grow - even in areas where hardscape and landscape elements are installed - but with “guidance.”
Do Root Barriers Work? How? Why?
Interestingly, there have been many studies done on the effectiveness of tree root barriers.
One of the most prominent examinations of deep root barrier effectiveness was a Dutch study that looked at 16 different root barrier treatments. The study found all 16 to be fairly ineffective, with the roots growing back to the surface over time. Thus, they concluded that for a root barrier to work well, it needed to:
- Be deep—ideally, extending below the primary root system
- Protrude above the ground level slightly
- Be UV resistant
Additional studies on the effectiveness of root barriers have come up with similar results and answers. According to the author on shadetreeexpert.com, additional information gleaned includes:
- Even if redirected roots resurface later, those roots tend to be smaller, weaker, and less intrusive.
- Deeper root barriers are more effective
- The root barrier should protrude above grade.
- A compact soil backfill after root barrier installation has the root barrier in place is helpful/.
- Using a gravel backfill under both hardscape elements and the root barrier might provide additional benefits.
- Root pruning prior to installation of root barriers is likely to be beneficial.
- The area below the tree’s drip line should be mulched with natural wood chips so that when they decay, they provide nutrients for the tree’s root system.
A Root Barrier That Really Works to Protect Sidewalks and Is Affordable Too? Meet Sidewalk Shield.
Referencing the aforementioned types of solutions, when considering a deep root barrier, you do have a few different choices. However, as also indicated, the best solution is going to be one that goes deep enough to sit below the root system, while also standing above ground level. Furthermore, UV resistance is important to have in a root barrier.
Sidewalk Shield is a tree deep root barrier that checks all of those boxes.
First, Sidewalk Shield comes in 3 different heights to cover a range of tree root depths—18 inch, 30 inch, and 60 inch. It is also 2.0mm thick for the 18 and 30 inch and 2.5mm thick for the 36 inch. Thus, it definitely meets - and in fact, greatly exceeds - the minimum-effective thickness for root barriers that work well.
Sidewalk Shield is also made of hearty HDPE-recycled polyethylene plastic that is UV-resistant and has a subterranean longevity of 100+ years. It comes in lengths of between 15 and 300 feet.
Another thing that is really nice about Sidewalk Shield is that it’s manufactured in rolls so it easily bends and is malleable into whatever shape or design is desired. This is a huge benefit since many other deep root barriers come in panels that are inflexible and therefore, don’t easily configure to more daring or circular/curved designs. This doesn’t make a huge difference below ground but on the above-ground protrusion, the straight-line panels won’t always be able to provide the desired aesthetic.
When installing Sidewalk Shield, remember… the purpose of a root barrier is to direct the root growth downward instead of out along the surface where it can do harm to sidewalks, driveways, septic systems, etc. Consequently, you want to position the material in a 10-degree downward slope. The top (portion closer to the soil surface) should be closer to the tree than the bottom. This creates a funnel to direct roots in a downward growth pattern.
When installed correctly, Sidewalk Shield should provide great benefit as a tree deep root barrier now and for many years to come.
 John Roberts, Nick Jackson and Mark Smith, Tree Roots in the Built Environment, Centre for Ecology & Hydrology, Natural Environment Research Council, London, 2006, p. 386.