It’s time to get to the root of it all.
ROOT (n) – “the usually underground part of a seed plant body that originates usually from the hypocotyl, functions as an organ of absorption, aeration, and food storage or as a means of anchorage and support, and differs from a stem especially in lacking nodes, buds, and leaves” *
*As per the Mirriam-Webster Dictionary
That is the definition of a root, as it relates to trees. They are there for support, food and air for them. They are essential to the life of all trees. In fact, a tree would not survive without its roots.
And yet we complain when they clog our drainage and sewer systems, crack our driveways, patios and walkways, and heave up asphalt in the road. How is that the fault of the tree though? When we plant trees too close to these items, there are bound to be problems. Most tree roots that are planted by the city only grow to a depth of 2-3 ft (60-90 cm). Instead, tree roots generally stay close to the surface of the ground, radiating outward. In this way, they maximize their air and water intake.
But how is it that tree root systems cause so much damage? In fact, it isn’t really the fault of tree roots at all. The larger roots are primarily there to anchor the tree. The smaller feeder roots provide the bulk of the water, air and nutrients that are needed for the trees survival. Both kinds of roots grow towards sources of water or air. An existing break in a pipe provides both water and air. If the breaks were not there, the roots would not grow there either. The same thing goes for cracks in foundation walls. The roots are just trying to gather their needs by whatever means possible.
What about the cracks and heaves where tree roots push on surfaces like sidewalks or driveways? Well, that isn’t truly the fault of the tree either. We can all see the effects of freezing weather on water right now (-11 C with the windchill making it feel like -18 C in London today) – it freezes. When water freezes, it expands. The same is true of ground water. What that means is that when water freezes under the ground, it takes up more space, causing heaving. It is actually frozen water that is doing the damage! In the spring, dormant tree roots become active again and grow into the spaces created by the now thawed ground water. The freeze/thaw cycle gets repeated every year, and eventually the tree roots look like the culprit for any warped walkways that you have.
So what is the answer? For starters, before planting a tree make sure that it is far enough from any existing foundations, patios, driveways or other walkways. A distance of about 5 ft or 1.5 m should suffice. After that, perhaps you should plant your trees upside down like they do in Africa with the Baobab tree?