Updated: Jun 30, 2020
Yesterday I wrote a post considering the value of plant roots. Often misunderstood and more commonly ignored, they generally only come to our thoughts for consideration when something goes wrong. We should though take more time to consider the value and purpose of roots and the risks associated with planting some plants in certain locations.
Yesterday's post came very close to publication. So close in fact that I was finalising most of the details, when my phone crashed and I lost the lot! Very disappointing and despite hoping that my words were not lost, they sadly were. As I tend to right blog posts in a stream of consciousness (albeit on a theme), I have no backup or notes to refer to, so I begin again. Equally as interested and I hope of value to any reader.
We should first establish that plant roots are often ignored when selecting plants. We very rarely think of them at all in fact. An out of sight, out of mind situation, I suppose. We should think a great deal more about them however. Roots represent the powerbase of most plants. The energy store. The water and nutrient gatherers. The anchors that both support them to the ground and that help to hold ground together. While they are vital for good plant growth in the majority of plants (especially those that we grow in the UK), they will never get the plaudits that foliage, flowers and fruit will. Even the form of trunks, stems and twigs will consistently receive more attention, as all of these elements are visible to us above ground.
In many cases, we only consider plant roots when a plant fails. A climber in a pot for example; starved of nutrient and unable to access enough water to sustain a voluminous canopy. Our when we forget to water a plant in a pot and when dead remove it to see the once fleshy roots desiccated and withered. Even the plant in a poorly drained pot or bed that rots and when removed we see mushy, black roots instead of the fresh white fibrous roots of a healthy specimen. It is the mark of a poor gardener to not learn from these mistakes.
Some issues are not related to the error of the gardener however. Some relate to our desires for a plant to behave against its natural behaviour.
One common issue that people encounter with plant roots is in the form of surface rooting trees. Apples (Malus) and Cherries (Prunus) are notorious for this, both pushing roots above the surface of lawns as they mature. These roots do seek out easy access to water, but are generally there to provide an anchor for the broad and weighty canopies of mature plants.
This surface rooting is rarely an actual problem, but I have met many a garden owner who hates this affront to their delicate sensibilities. Other than occasionally tripping on a surface root and equally rarely bouncing a lawnmower who's blade has struck a surface root, I have never seen them as an inconvenience. In fact in a garden, they could be used as a design feature to indicate the established age of a planting scheme. They can, of course, be an issue on roads, pavements, driveways and to buildings, though it is often not the roots that you see, but those that you don't that cause the worst damage.
The roots of street trees or ill-chosen garden specimens may well undermine pavements, roads and driveways and we should fundamentally consider why we are planting trees of any real size next to hardscape like this in the first place. Some modern selections may help to reduce risk by growing in a more upright manner, by reducing overall height, or by encouraging deeper routing, but trees will never sit well with construction in truth. No impossibly so, but often impractically.
By far the most common concern over roots that I have encountered over the many years that I have worked in Horticulture has been along the line of, 'Is my tree damaging my foundations?' I have heard it more times than I care to recall from clients as a Garden Consultant. Interestingly, I have not yet encountered anyone ask me if their tree is damaging their neighbour's property, though I have once or twice had people querying the potential damage from a neighbour's tree to their property and even their drains.
Put simply, trees are not well suited to planting near buildings: not just trees, any large plant, but trees particularly so. We do it a lot, but most are poor choices for the long term. While we can now protect buildings using Root Barriers, planting pits and Guards, we really should question why we are planting something so big, so close to our homes. It isn't impossible, but it may not always be sensible. We should think a great deal about species selection, maintenance regime to maintain size, planting specification to mitigate root development and reasoning for selecting a tree in the first place prior to making a purchase.
As a rule of thumb, consider two things. Firstly, trees that belong in a Woodland, Forest, or Parkland, really should only be planted in spaces of similar size. Mature Oaks are massive plants that are not well suited to the average domestic back garden. Secondly, when determining tree positions, imagine the width of the canopy at maturity (20 years+) and double it in terms of root spread. That is a reasonable, safe distance to consider to plant a tree from a building, thus preventing substantial roots from breaking through foundations and unsettling you in your sleep. That means that something like our native Oak, Quercus robur, should be some 30m away from the closest building to prevent roots from impacting on buildings. Speaking of impacting, we haven't (and indeed won't) consider root and soil impaction here, other than to note that it is another factor why a plant may fail and is often avoidable with better selection and more care for the plant itself.
While tree roots will seek out the easiest soil over weighty foundations, root movement is a very three dimensional process and roots that get under building foundations can be as damaging as those that break through them. We have all seen a mature tree that has been blown over as a result of unsettled, usually wet ground and strong winds in the winter. The roots of mature trees are massive and pull up whatever they are near to when the fall. Planting near buildings can cause an imbalance in radiating roots that makes winter wind falls all the more common. Like damage to buildings as a result of poorly chosen plant selections, this can be another nightmare of liability when it comes to insurance claims for structural damage.
Click here for a link to an insurer for their guidance on tree planting distances from buildings. Note1.
Some trees are definitely worse than others. In general, massive trees should be avoided in domestic gardens, but smaller, rapidly growing trees can be equally as dangerous. Two common problem trees to consider in terms of root damage are Willows (Salix sp.) a and Eucalyptus species. Both grow quickly and both drink huge amounts of water in summer and near nothing in winter. The resulting expansion and contraction of roots in soil can cause, at the very least, unsettling of the ground and often much worse if building foundations are involved. These are not the only trees that behave this way, but they (especially Willows) are particularly common at damaging structures with the way they grow underground.
So, if I can give just a few positive thoughts to aim for, consider the following;
1. Roots are valuable to most plants. Their purposes are varied, but never meaningless. We should think of them and provide for them when selecting plants for a project.
2. We should offer plant roots sufficient access to the space, nutrient, stable ground and water that will benefit the above element of the plant to give you what you want.
3. When considering trees for a domestic garden, think hard about the overall size of the tree not for now, but for the future (20 years +). Perhaps even so far in the future that you won't be around. Aim to select species that are better suited to the size of your space.
4. Good roots generally mean good plants, so we must value them higher than we typically do.
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Note 1. I neither endorse the company or website and I accept no responsibility for the specifics of the article or any issues relating to them. It is meant as a guide for consideration only.