Getting to the root of the matter
The Gardener's Corner
By Judith Rogers

We've all seen the roots of annual or perennial flowers when planting them and everyone should understand how important it is that the correct procedure beneficial to the plants be used.

Whether started from seed yourself or being removed from a pot, quite often the roots will be a tangled mass, growing and weaving throughout themselves.

When transplanting to the garden or a container, the roots need to be teased apart with your fingers so that they will spread out in the planting hole and hopefully grow away from the plant and into the soil towards stored moisture and nutrients. Like turf, if plants are watered often and without quantity, the roots know they must stay near the surface to take advantage of supplemental watering and will remain shallow.

Less frequent, deep watering will train the roots to grow deep, which is why weeds like dandelions have that long tap root to survive without water for long periods of time.

The role of roots is not only to absorb moisture and nutrients but to help anchor plants in the soil as well. Tucking the plant in deeply enough will ensure this role is carried out.

There has been speculation on the depth and spread of tree roots and book illustrations traditionally show a tap root extending deep into the soil with lateral branch roots extending from it. Fine hair roots grow from the lateral branches, which are usually near the soil surface.

The Environmental Horticulture Department at the University of Florida has done root excavation studies that suggest not all large trees have a tap root and that the lateral roots extend far beyond the drip line. The drip line is the term given to the outer circumference of the canopy of a tree or shrub where rain is shed to the ground.

Existence of a tap root depends on tree species, age, soil composition and whether the tree was grown in the field, from seed or transplanted from a nursery container. Oaks frequently develop a tap root whereas maples often do not and tap roots can become less noticeable as the tree ages and develops a widespread lateral root system.

When planting, tap roots of container grown trees are often severed, which causes the lateral branch roots to either grow down to form multiple tap roots or stay fairly shallow, depending on the soil.

Soil that is compacted or low in oxygen content causes the roots to grow close to the surface and this is evident on trees with and without tap roots.

Trees with tap roots are rarely found in urban developments where the soil is usually compacted from the heavy machinery. Is it any wonder then, when we have heavy winds, why it is common to see large trees blown over on their sides without very many roots exposed for such a big plant?

The root studies also proved that the lateral roots of specific species grow beyond the branch drip line and on average three times the spread of the branch crown. For three of the study species, more than 50 per cent of their roots were completely outside the drip line.

The findings from the study can assist arborists in diagnosing the decline and death of trees at construction sites and that those initially protected during construction are still susceptible to decline. This information may also influence the placement of fertilizers for shade and boulevard trees as the drip line may not be the plausible guide for placement.