How close is too close, when it comes to trees in your garden?

Did you know that you can damage your house hugely by what you plant in your garden? In the worst cases, the roots of trees can heave your greatest asset into the air making it almost worthless, or they can remove all the moisture from the ground causing great cracks outside your front door.

We are losing a huge amount of our trees because many do not understand how to assess how they might cause possible structural damage. Trees are being removed “willy-nilly” just in case there may be a problem in the future. When young trees are planted, it may take years for any problems to become apparent.

What will a tree demand in the way of water from the ground?

Some trees, such as the White Willow, will remove 100 gallons of water from the ground each day in the summer.  There are calculations that can be done which allow us to determine how far away a tree should be from a structure, depending on the height of the tree. The problem with this method is that trees grow, so it is necessary to work out how far a tree should be away based upon its maximum height. In the case of a White Willow, this would be 40m. This requires quite a large garden.

What will the roots do?

Trees can cause direct damage when they come in contact with a structure. Traditionalists assert that the roots of a tree mirror what is above the ground. This is too simple a model as roots will always grow in the direction that offers the least resistance. If there is rock below the surface of the ground, then roots will spread to a wider area than the visible parts above ground.

There are also many variations amongst tree species; for example, there are over 2000 species of Pine Tree and within the Willow family, a White Willow may grow into a tree exceeding 30m while the Eared Willow will rarely grow beyond 3-4m. In short, it is meaningless to assess how “a willow” might cause problems in the future, without a huge knowledge of all the different species.

Another factor often overlooked is the fact that many trees are grafted onto rootstock, and it is that rootstock that will determine how the roots grow and take on moisture and not what is above it!

How does the structure of the site make a difference?

Some soils are less shrinkable than others so the removal of water makes little difference. The worst soil for this is peat, which is highly shrinkable. Root growth requires oxygen levels in excess of 15% so clay soils near a structure will inhibit growth, leaving the building unaffected. The composition of the soil in terms of compaction will also have a bearing on root growth. High density soils will support less root growth.

The roots’ search for water is the dominant factor in root development. Reduced moisture levels encourage a root to grow further in order to find water.

Your lawn may be doing much more damage than your trees. Grass transpires a huge amount of water in summer. It can suck out all of the moisture to a depth of 0.5m and by early summer competes fiercely with the trees. The grass also stops the rain water from getting down to the roots.

Roots are always looking for moisture. It goes to follow that a root will search out any imperfection in a drain and exploit it to get at the moisture. Before you know it, your drains are blocked with roots.

Best advice, before removing your beautiful 100 year old tree, would always be to seek the expertise of a Chartered Surveyor, who may in turn need to consult with other experts such as arboriculturists and soil experts. Many trees are removed unnecessarily and in many cases, were causing no problems to surrounding structures.

Read our other article about trees in this newsletter here.

*Back to September 2016 Newsletter*

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