Urban Tree Legends Revealed

Most people will agree with the International Society of Arboriculture when they say, “Trees are Good”. However, there are still some “tree myths” (or “urban tree legends”) that need to be acknowledged and refuted. The following list comes from common questions posed to Tree Canada from school officials and homeowners. They include:


1. “Tree roots seek out and break up foundations”

Tree roots cannot live in sterile mediums such as concrete and will never seek to penetrate foundation walls, instead, tree roots will seek moisture and may enter leaking pipes (or foundations) in search of moisture

SOLUTION: Ensure your stormwater and other drains are not leaking

In certain cases there may exist a unique combination of factors which allows foundation walls to crack – this includes: the use of specific soils (such as marine clays) to be backfilled against buildings, the conveyance of surface water from rooftops and roads to stormwater sewers, periods of prolonged drought, and where trees are also present withdrawing large quantities of water from the soil, the soils may shrink which allows the foundation to move in an outwards direction potentially cracking the foundation.

SOLUTION: Do not use clay as a backfill to your building, ensure as much surface water as possible is allowed to drain onto your soils and not a stormwater drain and choose a species of tree who does not have a huge thirst for water (e.g. do not choose silver maple Acer saccharinum)


2. “Tree branches can Damage my Windows”

Tree branches will only damage windows if you increase the risk of this happening.  The right tree planted at a safe distance from a structure is harmless.

SOLUTION: Choose your tree species carefully, know the spread of the mature tree and allow enough space for the mature crown to grow short of your window – keep your trees well pruned


3. “Kids will climb trees and fall if planted in the schoolyard or backyard”

Kids climb and may fall from a lot of things but that does not mean they should all be banned from the schoolyard.

SOLUTION: Trees can be pruned or otherwise protected to deter this.


4. “Criminals hide in bushes and behind trees – it is better if they are not there”

Criminals also can hide behind vehicles and dumpsters!  There are many studies that show that the presence of green space including trees and shrubs is a large deterrent to anti-social behaviour including Attention Deficit Disorder, graffiti and domestic violence

SOLUTION: Good design, the thoughtful placement of trees and shrubs, and pruning will ensure visibility and safety.


5. “Cleaning up after leaves is a nuisance”

Leaves have great play value, and they are nature’s food for the soil, they can be used as mulch on grass, under trees, in gardens and for composting.

SOLUTION: Plant more conifer trees and/or learn to use leaves for compost


6. “There’s no use planting trees - trees and greenery just get vandalized”

Not really an excuse to not plant trees but by increasing a sense of ownership can reduce all vandalism

SOLUTION: Involve students from the outset of the project, plant large (caliper) trees that have a better chance of surviving, develop a maintenance plan that includes responding to damaged plants/involve the community in maintenance, provide signage as to the benefits of plants to society


7. “The more trees you pack into a space, the better”

Trees will compete with each other for water and nutrients when planted too close together and can be harmful to the tree’s growth because it will impede the proper characteristics for crown development. 

SOLUTION: Plan your planting according to the full size the tree will grow at maturity as well as consider what shade tolerance and soil type your tree will need.


8. “Planting bigger trees is always better than smaller seedlings”

Younger, smaller-sized trees have a higher number of roots than do older, larger-sized trees.  Trees rely on stored starches in their roots when they are being transplanted until enough new roots are grown to sustain tree growth.   Transplanting a bigger tree means it has to exist on its stored starches in a lower number of roots so it is more stressful for a larger tree to be transplanted than a younger tree.

SOLUTION: Plant as young a tree with a healthy root system as your site will allow – certainly in high traffic areas larger trees will be needed.

9. “There is no big trick to digging a hole to plant a tree – all holes are basically the same”

The roots of a tree cannot properly develop in an opening that is too narrow, too deep, or with edges that are too straight.

SOLUTION: When preparing a hole for your new tree, it is important to dig a wide, soup-bowl shaped hole.  The hole should be only as deep as the root mass of the tree with the soil depth coinciding to the depth that the tree was growing in the nursery – the walls of the hole should be roughed up to provide space and a hospitable environment for root development into the new soil.


10. “To help offset root loss during planting, you should always cut back the top of the tree”

Removing the top of the tree will impede healthy growth because it reduces the tree’s capacity to photosynthize.  The tree’s crown form, structure and development will be negatively affected by the removal of the top live limbs.

SOLUTION: Only the diseased, damaged or dead wood should be removed during the first 5-10 years after planting the tree.


11. “Enhance your planting site with as much compost-rich top soil as possible to ensure growth”

When a tree is planted in soil that is radically different than the original soil it is growing in, or when new soil is too rich, it can be harmful to the tree as the roots will refuse to grow outside the planting hole, creating problems for the tree’s roots not anchoring properly. Roots can grow in a girdling condition if the new soil they are planted in is very different than the soil it has originally grown in.  When a tree is planted near a permanent structure made of concrete (i.e. retaining wall, house), roots may become girdled by being deflected from the structures. 

SOLUTION: The soil you are planting in should not be radically changed or augmented with compost, try to leave the soil conditions as native as possible. The tree’s roots should be loosened up to encourage them to grow out and any girdling roots should be cut away when the tree is taken out of a container.       


12. “After planting a larger tree, it must be braced and staked”

This is often unnecessary, except where there is bare root planting in a windy area where or where you are planting on a slope - trees need to develop a strong support and reaction to wind and sway is important to ensure that it develops this wood. Unfortunately too often the stakes and wires are left on too long and the tree grows into these.

SOLUTION: When only necessary, attach the tree to a stake at a minimum height that keeps it from falling over, which avoids injury to the trunk for a maximum of one growing season


13. “Grass, flowers and trees can easily coexist”

Grass, flowers and trees are in competition as they are each looking for water and soil nutrients, which may be limited, quite frequently lawn mowers and trimmers damage tree bark if not used properly, maintaining flowers involves digging up soil which can damage tree roots

SOLUTION: Keep your trees in a separate raised bed and remove the grass by at least 0.3 m (1 foot) away from base of tree base, which can then be mulched to preserve moisture and restrict weed production


14. “The more mulch the better”

Too much mulch can damage root growth as it creates low soil oxygen but high moisture levels and can cause insect root rot and other diseases, and affect soil pH or soil nitrogen levels

SOLUTION: Use bark or living perennial mulch, more inert than wood chips, to a maximum depth of three to eight cm (1”-3”)


15. “Fertilize soon and often”

Fertilizer contains one or more elements required for tree growth but should not be thought of as “food” – it is like a vitamin, not a meal and can actually stress newly-planted trees

SOLUTION:  Use a well balanced fertilizer (10-10-10) if soil and leaves appear to be deficient and/or two years before, or two years after any root injury but not soon after tree is newly-planted.


16. “Control all Insects as soon as Possible”

There are many insects who simply need trees for survival and do not harm them and can be helpful in controlling other insects that may harm trees

SOLUTION:  Identify insects found on the tree to see which are beneficial and which are not before attempting to control them