Myth 3: All trees have tap roots
A tap root is an enlarged and usually tapered root that grows vertically downward. It forms the centre root structure from which other smaller roots spread out laterally. The dandelion, for instance, provides an excellent example of a tap root. However, very few (if any) trees in an urban setting have tap roots. This is because when the water table is close to the soil surface or the soil is compacted or clay-heavy, tap roots do not develop.
Basic tree biology tells us all roots need oxygen to survive. This is why roots are typically located in the top 1 m (3 ft) of soil; they get air from the fine roots absorbing the oxygen located in air pockets within the soil. If a tree had tap roots, how would it get this much-needed oxygen?
Myth 4: Tree roots do not expand beyond the drip line
A tree’s root system holds the key to its survival. At construction sites, protecting tree roots is the most important step to keep existing trees healthy. Unfortunately, most people do not understand tree biology, and may have mistaken ideas about tree growth.
As a tree grows in height, it requires more oxygen. As a result, the finer roots extend well beyond the drip lines of the branches (i.e. the area directly under the outer edges of the tree branches). Frequently, roots extend from the trunk as far as the tree is tall. In fact, the root system on trees and shrubs planted in a given landscape can grow up to three times the distance of the tree’s branch spread within a few years of planting.
Since most of the root system is in the top metre of soil, finer roots are concentrated in the top several centimetres of soil. Therefore, any soil disturbances, major or minor, can injure or remove a large portion of the absorbing roots. Excavation, topsoil removal and trenching activities that cut roots will prevent trees from absorbing critical supplies of water and nutrients.
This is of particular importance when dealing with existing trees on a project site. During construction, keeping equipment and trucks away from the tree trunk is not enough to prevent damage, as they will compact the soil, squishing out air spaces in the root zones. Damaging roots on one side of a tree may cause branch dieback on that side only or in random areas throughout the crown. Even then, damage may not be immediately evident. Trees store energy in their branches and trunks, which they use to survive after roots are damaged. It may take two or three years to notice any decline, and up to five or 10 years before root damage leads to tree death.
Since many of the fine roots are located close to the soil surface, one must also take great caution when changing soil grades. Even adjustments as small as 150 mm (6 in.) can cause extensive root system damage. Soil should never be added to or removed from the area within the drip line of an existing tree that is to be saved.
When adding new trees into the landscape, remember to choose the right tree for the location. One should consider avoiding the planting of large fruited trees over, or adjacent to patios, pools, decks and spas. Trees that produce fruits and berries can also potentially stain the patio and furniture, although certain cultivars with small or persistent fruit will not drop and cause a mess.
Any new tree plantings should be made at a distance from any pool or spa installation. The exact closeness of the tree depends on the variety and growth habits. Also remember that the hole dug for planting should be at least two to three times the width of the root ball; this will set the tree a minimum distance from the pool or spa under ideal conditions.
