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By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

Tree Roots Aren’t Where Once Thought

We are just now learning what a tree’s root system really looks like and this new knowledge is having far reaching effects. This information can assist us in diagnosing tree decline and death following construction, influence the placement of fertilizer and help us to make decisions about the proper planting of trees in the landscape.

Recent root excavation studies at the University of Florida and other institutions have yielded some surprising facts:

Fact 1: Lateral roots extend far beyond the drip line or canopy of the tree, with over half of the roots being beyond the tips of the branches. On average, tree roots spread close to 3 times the spread of the branches. A tree with a 10 foot wide canopy would therefore have a 30 foot wide root spread.

Fact 2: The fine “feeder” roots are concentrated within the top 12 inches of soil with many in the top 2 inches.

Fact 3: Roots grow even closer to the surface in soil that is highly compacted or low in oxygen content. In urban environments, where the soil is often compacted taproots are rarely found.

These facts should dramatically change the way that we protect and care for trees. Though we have done a better job of protecting the trunks and branches in recent years, there have been some seriously mistreated root systems during property development.

Now that we know the roots are far reaching and shallow it is easy to see why so many trees decline following soil disturbance. Any of the following practices can kill directly or weaken the tree, resulting in death years later.

■ Ditching too close to established trees results in the cutting of a major portion of the root system.

■ A cut in grade of only a few inches can remove many of the fine feeder roots that the tree uses to absorb nutrients and water. If removed, the tree must use stored energy in an attempt to regenerate them.

■ An excessively deep layer of fill soil over the root system can result in suffocation. Since tree roots require atmospheric oxygen, they establish themselves at the optimum soil depth for both oxygen and moisture. Any drastic change can have long term negative effects.

The key to keeping the roots of an established tree healthy is leaving them alone. Large, more mature trees are especially susceptible to damage from soil disturbance. This fact becomes obvious when the life span of rural trees is compared to urban trees. Rural trees live about 10 times longer.

Usable Tree Trivia

● Not all trees have tap roots and of those that do, they are non existent or less prominent on older trees.

● The Southern Magnolia has a root spread of almost 4 times the branch spread.

● Old oaks with severely damaged root systems might appear healthy for 2 to 3 years and live for 5 to 10 years before succumbing.

● Young trees like young people, adapt better to a drastic change in their environment and have a better chance of recovering.