GET QUOTESRoot Pruning: Improving Tree Health and Simplifying Relocation
GET A FREE ESTIMATE
Edited by Ali Lijee Edited by Ali LijeeOur network of local tree surgeons and arborists in the UK provides root pruning services to keep trees healthy and prepare them for transplanting.
Tree roots are an essential part of the tree’s overall biology and are just as important as the tree’s canopy for helping the tree remain stable, healthy, and well-nourished. They absorb water and nutrients from the soil, feeding it back up to assist with photosynthesis. But at times, tree roots can pose a hazard or a nuisance and may need to be pared back. Often, pruning is quite important for helping a tree survive in a new environment, which is why root pruning is commonly tied closely with tree relocation and transplanting.
Table of contents
- What is root pruning?
- Why is root pruning needed?
- The root pruning process explained
- Root pruning methods for planted trees
- Root pruning for container trees
- Professional root pruning vs DIY: how to decide
- How to get root pruning near you
- Root pruning in the UK: frequently asked questions
- Get a root pruning quote today
What is root pruning?
Root pruning is the process of trimming roots from a tree in order to promote healthy new growth. It’s very commonly needed as part of the tree relocation process, generally half a year in advance of uprooting and moving the tree. It’s also quite common for potted plants such as container trees to keep them healthy and to manage root spread.
Long roots sometimes need to be pruned back so that new growth remains close to the trunk for the tree’s health and vitality, but at other times it may be needed to protect infrastructure such as underground foundation walls, pavement, or nearby roads. In this latter case, root pruning is injurious and generally isn’t the preferred option for long-term tree care. Better engineering is preferred.
By paring back roots, new root growth is easier to manage as they emerge from the root ball and remain near the trunk at first. This allows uprooted trees to keep much of their root ball intact, which in turn lessens transplant shock once the tree is planted in a new location.
Root pruning is often part of an overall tree relocation service provided by tree surgeons or arborists, but it’s also something that many homeowners and avid gardeners can enjoy doing on their own.
Why is root pruning needed?
Root pruning may be necessary in certain circumstances, such as:
- Prepare the tree for replanting: whether for container trees from a garden nursery or existing trees in the ground, root pruning is commonly required as one of the most critical steps before extracting them from the ground (or container) for replanting purposes.
- Minimise hazards to property and infrastructure: while not ideal, root pruning may sometimes be needed to selectively eliminate roots from urban trees which interfere with pavement, building foundations, and so on.
- Promoting healthy tree & root growth: Careful, selective root pruning can encourage vigorous and healthy regrowth, and by making the tree’s roots healthier, the entire tree may also see health benefits.
- Manage tree size: pruning can be an effective way to control and manage the size and growth of trees..
Benefits of root pruning
There are some benefits to root pruning, which include:
- Easier to transplant the root ball: when a tree’s roots are pruned in anticipation of transplanting, it will be easier to wrap burlap around the root ball and contain the mass during transport.
- Reduced shock from transplanting: small root ball which have been pruned away can often adapt much better to new soil environments after replanting, thereby reducing the shock that trees go through.
- Healthier growth: as with pruning branches from the tree’s canopy, pruning roots can allow for healthier regrowth to come in by eliminating diseased or dying roots.
- Less intake of water and nutrients: after roots have been pared back, there will be less demand for water and nutrients from the soil to nourish the tree, which can help replenish soil.
Root pruning is commonly needed before transplanting a tree to reduce shock and promote vitality
The root pruning process explained
In general, all pruning should be done whilst the tree is still dormant, which for most species is late autumn and winter, so that new vigorous growth can come through in the spring.
Furthermore, pruning cuts should always be made with sharp and clean tools so as not to introduce wounds and pests and diseases. Refrain from cutting small roots measuring less than one inch (about 2.5cm) in diameter and do not cut roots with more than a three inch (7.5cm) diameter. In other words, you should only be trying to prune roots that are between 1-3 inches in diameter.
Depending on the size of the root, suitable tools for pruning may include secateurs, pruning saws, or loppers. Always aim for clean cuts and sharpen/sanitise tools as necessary.
Assuming that cuts are made properly, two of the most important considerations for root pruning are getting the season right and placing the cuts at the correct minimum distance away from the trunk.
How to determine the placement of root cuts
Root cuts should be made as far away from the trunk as possible, but of course the purpose is to reduce their spread which means that cuts need to be made closer to the trunk. Any cuts made beyond the spread of the overhead canopy will normally be perfectly fine for tree health, but the closer one gets to the trunk, the more possibility there is for permanent damage to the tree or hazardous structural imbalances.
How far away from the trunk should cuts be made? Tree surgeons and arborists generally use a rule of thumb to determine the optimal distance from the tree trunk to begin pruning. The minimum distance ensures that risks to the tree’s health are minimised.
The method of calculating this distance is done by measuring (or estimating) the diameter at breast height (DBH). This is roughly at around 4.5 ft (around 1.3m) up the trunk from the ground. Professional arborists use callipers and girthing tape to get a much more accurate figure, but you can measure it quite accurately yourself by measuring the circumference with flexible measuring tape.
Wrap the measuring tape around the tree’s trunk at around 4.5 ft up the trunk, then use a calculator to determine the diameter. The formula for a circle’s diameter (d), given its circumference (c), is circumference divided by π (3.14…), or:
d=c/π
For example, if you measured the tree trunk circumference as 500cm, the diameter is:
d=500cm/π=159.155cm, rounded up to 160cm, or around 5 ft 3 in.
If roots need to be cut all around the tree, the minimum root cut distance away from the trunk should be at least 5 times the DBH. Using the above example for a 500cm diameter tree, the minimum root cut distance would be:
5×160cm=800cm, or around 26 ft 3 in.
If roots need only to be cut on one side of the tree, the minimum root cut distance should be at least 3 times the DBH. Using the same example as above, the minimum root cut distance away from the trunk would be:
3×160cm=480cm, or around 15 ft 9 in.
In any case, if the tree’s roots have signs of decay or if there is pavement over the roots, it’s always better to be more conservative and prune further away (ideally 5-6 times DBH).
Aftercare and monitoring
Pruning away roots means that there will be fewer roots sucking up water and nutrients from the soil directly afterwards, but as they regrow they will need plenty of both. Don’t prune roots if there is a drought and make sure that there will be enough rainfall afterwards (you’ll have to water the trees yourself if there isn’t).
Once roots have been pruned, soil should always be remediated. This may involve backfilling excavated earth with fresh new soil, applying fertiliser treatment (but not directly afterwards, wait a little while), and mulching. Of all of these, mulching is one of the most important as it helps to prevent excess moisture from being lost and it decays and feeds the soil with fresh nutrients.
Adequate aftercare helps to ensure that the tree roots are growing in a healthy environment, which limits the risks of disease or decay.
Root pruning methods for planted trees
There are various methods of pruning a bare tree’s (i.e. a tree planted in soil and not in a container) roots. Below are the most commonly used techniques for root pruning:
Manual spading
The first and most practical method for small trees with manageable roots is to manually spade through the soil. The simplest approach is to calculate the minimum distance from the trunk at DBH, then begin driving the spade into the ground, making a circle along the perimeter. By driving the spade into the ground at the height of the spade, many roots will be cut and there will be no need to excavate further. The downside to this approach is that spade cuts are indiscriminate.
For a more thorough approach, use the same minimum distance as calculated above, then shovel out a trench along the outside of that perimeter. Ideally, you should spade about a foot wide and a foot deep. Many exposed roots can be cut or left as-is, depending on their size, and the entire trench you’ve dug out can be refilled with fresh new soil and topped with a layer of compost or mulch.
Mechanical root cutting
Similar to manual spading, mechanical root cutting essentially does the same thing except with heavy machinery called root pruners. It’s much faster to cut through roots with a root pruner, and the device looks and operates much like a stump grinder used for tree stump grinding.
The root pruner rips through the soil and makes fairly clean cuts to all roots. It’s for this reason that mechanical root pruning can be seen as quite reckless, since it might eliminate some big roots that may not heal as well as small feeder roots, which should be left alone. The operator can guide it along the perimeter relatively quickly, which makes it convenient for many people.
Trenching
Trenching or excavating with heavy machinery is commonly done in confined areas or spaces where other methods are impractical, although it is the worst for tree health and should be avoided unless it’s the only option available.
With a chain trencher or excavator, entire sections (trenches) are dug through the earth. Unlike root pruners which cut straight down, however, excavators use strong shearing forces which push and pull through the earth. This can result in many roots being torn, having damaged ends, and causing immense stress to inner roots near the trunk.
There are many manual and mechanical methods of root pruning, each with its own advantages and disadvantages
Root pruning for container trees
A very popular method of growing trees in the UK is with containers or large pots. Container trees are often beneficial when homeowners lack the space, lack suitable ground soil conditions, or simply prefer the appearance of a potted tree.
Since these trees aren’t growing in normal soil conditions where the roots can freely spread, they will occupy as much space as possible within the container. This means that regular root pruning is essential for maintaining the tree’s vitality.
Container trees have a higher chance of girdling and wrapping their roots around in a circle, which can stunt the tree’s growth or lead to a lack of nutrient uptake. Moreover, container soil tends to be compact, so water may not percolate through as easily and the pot can become waterlogged. This, in turn, tends to lead to higher disease rates for container trees.
The solution to these problems is root pruning, performed ideally every 2-3 years. As with ordinary outdoor tree root pruning, container trees should be pruned during their dormant season, which normally stretches from late autumn to the beginning of spring. If the species is known to grow quickly, consider pruning every 1-2 years instead.
To trim container tree roots, remove the entire tree from the container. Begin by inspecting the root ball for any signs of disease or rotten (usually dark and mushy) roots and pruning these off. Then, begin to prune around the perimeter of the root ball and underneath, removing about 10-20% of the total mass. Leave any stringy, hairy roots in place. Replace the tree in the container and fill with new, nutrient-rich soil. Keep moist and refrain from fertilising the tree directly afterwards.
Container trees benefit immensely from routine root pruning
Professional root pruning vs DIY: how to decide
Unlike many of the tree care services provided by professional tree surgeons and arborists in the UK, tree pruning is generally one of the safest to DIY so long as you follow a few basic steps. Knowing when to prune, how far away from the trunk to prune, and which types of roots are okay to prune (1-3 inches), and doing so with sharp and clean hand tools, all contribute to keeping your tree roots healthy.
For anyone in need of professional root pruning, such as to relocate a tree or to perform utility or roadworks that require trenching, however, qualified tree surgeons or arborists should be consulted.
Tree root pruning is often safe and ideal as a DIY job
How to get root pruning near you
Whether you need to relocate one or more trees on your property or to another location altogether, or require professional assistance to prune roots that may be interfering with infrastructure or buildings, it’s always a good idea to contact a qualified tree surgeon or arborist.
TreeMend has hundreds of local tree surgeons and arborists across the UK ready to assist property owners, land developers, and local councils with professional root pruning as well as a wide range of other essential tree surgery services.
Get a no-obligation quote for root pruning from a tree surgeon or arborist in the UK with TreeMend
Root pruning in the UK: frequently asked questions
Can you cut the roots of a tree without killing it?
Yes, you can cut the roots of a tree without killing it provided that you follow a few general rules. Firstly, try to only cut roots that are 1-3 inches in diameter. Secondly, make sure that you’re cutting roots from a minimum distance from the trunk of about 3x the tree’s diameter at breast height, or ideally 5x that figure.
Should you prune tree roots?
Tree roots normally don’t need to be pruned unless the tree needs to be relocated and replanted elsewhere, if roots are interfering with property or infrastructure, or if the tree is planted in a container.
What is the rule of thumb for cutting tree roots?
The rule of thumb for cutting tree roots is to keep cuts to roots measuring 1-3 inches in diameter and to always cut at least 3x (5x is ideal) the tree trunk’s diameter away from the trunk. In other words, if the trunk measures about 12 inches at its diameter, cuts should be made 36 inches away from the trunk (60 inches is safer).
Is it okay to cut through tree roots?
Yes, it’s okay to cut through tree roots so long as the roots aren’t too thick (over 3 inches in diameter) and you aren’t interfering too much with feeder roots or baby roots less than 1 inch in diameter.
What happens if you cut the main root of a tree?
If the main root(s) of a tree are cut, the tree could suffer or even die. The largest roots of a tree give it structural stability and keep it stabilised with the trunk and crown, so a tree could be severely imbalance if its root system is heavily interfered with. In terms of tree health, cutting through the main roots could leave wounds that attract disease and this could leave permanent damage or even kill the tree.
Do tree roots keep growing once a tree is cut down?
Yes, tree roots can continue to grow underground even after a tree has been felled. A tree stump will often produce new shoots from the stool (the stump), and roots underneath can continue to grow.
When should I not prune trees?
You should not prune trees or their roots during the regrowth season. For most tree species, and especially deciduous leafy species, this is during the spring. Roots should be cut a full year to half a year in advance if they need to be transplanted, but try to avoid cutting during the growth season.
Do roots grow back if you cut them?
Yes, tree roots will often continue to grow if you cut them. Some tree species will grow back their roots vigorously and quickly, such as Elm or Willow trees; others, such as Maple and Oak, may not tolerate excessive root pruning and could even die if their roots are too heavily pruned.
How many roots can be cut without killing the tree?
It’s generally safe to remove around 10-20% of a tree’s roots without causing permanent damage or killing the tree. Much like a tree’s crown, no more than about 25% of the tree roots should be removed in one pruning session. Excessive root pruning can kill the tree.
What saw to cut tree roots?
The best saw for cutting through tree roots should be a professional pruning saw used by arborists in the UK. Small roots can be pared back with secateurs, larger roots with loppers, but tough roots are often easiest cut with a pruning saw.
Get a root pruning quote today
Do you need assistance pruning roots for one or more trees on your property? TreeMend puts you in direct contact with vetted and approved tree surgeons and arborists across the UK. Get a no-obligation quote for tree root pruning today.