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cause a lot of damage
Aggressive root systems can cause a lot of damage

Trees are the foundation of our northern landscapes; every effective landscape invariably utilizes one or more of them to bring depth, stability and a vertical dimension to the composition. But trees can't just be planted anywhere in the landscape, and one of the primary reasons is that their roots don't always play nicely with other below-ground or surface elements. In fact, over time, aggressive root systems can cause serious damage to landscape structures and utilities, most importantly our homes, and the problem can be extremely difficult and expensive to correct.

The best solution to problems with tree roots is prevention and understanding - this is one common affliction of homeowners that is 100% avoidable. So whether you're doing up a new landscape, renovating a tired one, or just adding one or two trees to an existing landscape, a little knowledge now could save you a ton of heartache down the road. And since Northscaping is in the knowledge business for northern homeowners and gardeners, and you're a northern homeowner, you owe it to yourself to read on!

Anatomy Of Destruction

It goes without saying that roots are a critical component of a tree's anatomy. They absorb moisture from the ground and transport it along with nutrients from the soil up to the growing above-ground parts of the tree. They also secure the tree to the earth, anchoring it against the forces of driving winds and rains. Given these two primary purposes, it should come as no surprise that root systems grow deep and wide, to tap reserves of moisture and solidly affix the tree in place.

While all trees certainly have roots, different species have different natures of root systems, depending on their cultural preferences and evolutionary adaptation. Some trees, like oaks, have lengthy taproots that drill deep into the ground, with less extensive lateral roots. Others have very shallow roots that extend great distances from the trees. Some, like pine trees, have fine and shallow root systems optimized for growing in rocky and sandy soils.

And some of the "heavy feeders" have extensive root systems that extend both deep and wide, with enormous roots that grow to become the diameter of large branches. These are generally the plants that are the most damaging to our homes and gardens if improperly sited. But from where do these roots get their "strength"? After all, doesn't it take great strength to buckle concrete and crack drainage tiles?

extensive roots
Large trees can have extensive roots that extend well away from the tree

Surprisingly, while relatively slow-growing, the plant tissues in the roots can build up incredible pressure as they grow. The cells that comprise these tissues wedge themselves between anchor points and exert pressure as new cells are added. As well, the changing moisture levels in the water-conducting roots cause them to expand and contract, often at different rates than the surrounding soil and features. And finally ground frost plays havoc on the earth in winter, resulting in the shifting and movement of the soil. Because they are solidly anchored, tree roots do not shift to the same extent, and the resulting pressure can be incredible.

Then there's the obvious fact that roots exist to gather moisture and feed it up to the above-ground parts of the tree. As such, they are highly effective at sucking the moisture out of large swaths of earth. This can create a virtual drought underneath a tree, which is further exacerbated by the canopy of leaves which acts almost like an umbrella. The resulting perpetual drought makes it extremely difficult to grow other plants in these "rain-shadows" around mature trees. And if the trees are shallow-rooted, the tangled mass of roots can eventually choke out the weaker plants.

Tree Roots Around The Home

Trees and houses were never really meant to be in close proximity to one another for a multitude of reasons. Trees can break in a windstorm and fall on a house, and the leaves fall into the gutters and clog them. But far and away the greatest risk to a house is the damage that tree roots can inflict.

Invasive tree roots can cause serious damage to the foundations of homes. As the roots increase in diameter, they wedge themselves between the basement wall and the surrounding soil, creating more pressure with each passing year. The pressure they can exert, especially in conjunction with the expansion and contraction of frost heave, can actually crack basement walls. And removal is not always an easy solution; the decaying roots eventually become conduits for water and frost and lose their structural integrity, increasing rather than decreasing the stresses on the foundation.

Home foundations and basements are designed to guide any water that does not drain away from the house down the walls and into a drainage system underneath the basement floor, which eventually collects in the sump pit for periodic removal. Without this system, basements would flood with regularity. But invasive roots will also grow down and along basement walls, eventually reaching these drainage systems and clogging them. Many basement drainage problems in older homes are a result of mature tree roots having all but disabled the in-built mechanisms that should have kept them dry.

Massive cottonwoods
Massive cottonwoods should never be planted near a home

Tree roots can be damaging to homes even if they're planted a distance away from the house. If planted near buried utility lines such as electricity and gas, they can eventually create additional stresses that these were not meant to handle. If trees with aggressive roots are planted above water and sewer lines, the roots can exert enormous stresses as they wrap around them, eventually cracking or crushing them. They then continue to grow into these cracks, and it's not uncommon to find tree roots completely obstructing a sewer line to a home!

As many unfortunate homeowners discover, invasive tree roots can also cause phenomenal damage to driveways, sidewalks and patios. The majority of these landscape structures simply sit atop the surface of the earth, perhaps with some drainage elements underneath if they were properly designed. But they were never intended to tolerate the enormous forces of growing tree roots, which can ultimately shift, lift or crack entire pads of concrete. Many a sidewalk has been lost to an aggressive root system from a nearby tree.

Tree Species With Invasive Roots

Different trees have different types of root systems. A few are relatively fine and compact, but by and large the majority will have root systems which extend down and outwards in balance with the top growth of the tree. For most trees, the roots extend outwards just a little further than the canopy of the tree (identifiable by the shadow that the canopy would create on the ground below if the sun were directly overhead), and to a depth similar to the height of the tree. Of course this is only a rule of thumb, as every tree is different.

But some species of trees go well beyond these typical ranges, and these are the ones that merit special attention from northern homeowners and gardeners. Often these trees are the real "survivors", ones that have adapted vigorous root systems to buffer them against prolonged periods of drought or windy exposures on the tops of hills or open plains. The aggressiveness of their root systems serves them well in their native environment, but can become a nuisance in a controlled urban landscape.

Here are a few common northern trees with particularly invasive or aggressive root systems;

  • Poplars, Cottonwoods and Aspens (Populus spp.) - nearly all species and varieties - enormous and wide-spreading root systems that desperately seek out moisture, one of the worst to plant near homes or gardens
  • Willows (Salix spp.) - any of the tree species - extensive root systems anchor willows in their native wet environments and run deep looking for moisture, another to keep far away from homes
  • American Elm (Ulmus americana) - a favorite urban tree, but one with deep roots that commonly clog drains and sewer lines; keep well away from anything related to water
  • Silver Maple (Acer saccharinum) - shallow and dense roots, plant well away from homes and forget about planting any gardens nearby!

Generally speaking, larger shade trees, either in terms of height or spread or both, will have wider-reaching roots than their smaller ornamental counterparts. As well, deciduous trees tend to have more extensive root systems than evergreens and conifers, which tend to have shallower root systems.

Tips At Planting Time

The whole key to protecting your property from the inevitable damage of tree roots is in the planting stage - when it comes to managing tree roots, nothing beats proper planning at the very beginning. It's far easier to put a tree in the right place when it's tiny than to try and design the structures to work with or around an improperly planted tree, or worse to have to correct the damage caused by one years down the road.

Know something about the roots of the tree you're planting

Before you place a tree in the ground, it is imperative to know a few things about this tree, and in particular the nature of its root system. If it's one of the species listed above, you should exercise additional caution in the planning stage, and understand the extent of the root system in terms of both depth and spread. So if the tree has aggressive spreading roots, you should keep it a fair distance from the house, a minimum of 25' and much safer, 50'. If it has deep and water-hungry roots, you'll want to plant it at least 20-30' from water and sewer pipes, or from any buried utility lines for that matter. And if the tree has shallow, wide-spreading roots, you'll want to keep gardens well away.

But the relative "invasiveness" of a tree's root system is also a question of degree. Just because a certain tree isn't know to have aggressive roots, this does not immediately imply that it can be planted right up against a house. Trees are still trees, and it takes a lot of moisture and below-ground structure to keep them alive and secure, no matter how dainty or delicate they may seem. Almost any tree planted 5' from the foundation of a house is capable of causing problems down the road.

So as a general rule of thumb, no tree of any variety should ever be planted closer than 10' from the foundation of basement of a house. The larger the tree is, or the more aggressive the root system, the further away it should be planted, increasing to a safe distance of as much as 50' for the most aggressive varieties. Likewise, a minimum boundary of 5-10' should be maintained between a tree and any underground utilities. And no tree should be planted closer than 10' to any driveway, sidewalk or patio, a number which should be increased to 20' or more for species with aggressive shallow roots.

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