Urban Horticulture Myth: Tree Roots Look Like the Canopy

Myth: Tree Roots are evenly distributed under the tree canopy and the distribution and appearance is like the canopy (What you see above ground is what is underground).

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Fact: Nothing could be further from the truth. Tree roots are advantageous seeking food and water and have no relationship in habit or population to the canopy except that healthy canopies indicate more roots (or better yet strong healthy roots make thick dense canopies)

Origin of the Myth

Perhaps the myth comes from all the drawings depicting roots as a mirror image of the canopy. The reality is the roots adventure off in all directions, clustering in fertile areas and avoids infertile areas. Sometimes the cluster of roots is so dense that growing grass on them is nearly impossible – something akin to growing grass on a piece of 12" thick plywood. The roots populate the surface – especially Live Oaks.

What Tree Roots Really Look Like Below Ground

A better way to imagine the tree roots is thinking of random cities placed about the "countryside" near the tree. These cities are mining towns that mine nutrients and water. Where there is a good resource the towns grow and prosper. Some towns grow to be large cities and others stay small towns. Regardless there is little rhyme or reason to the placement or growth – it is totally random, only the tree knows the reason.

Growing Grass On a Stack of Lumber

A cluster of roots effectively eliminates turf from receiving the water and nutrients needed to survive. Most people incorrectly blame poor sunlight as the cause for this problem and thin out the trees to provide more light. In some cases this seems to work – probably because the shock of pruning reduces roots. Yet with time the problem reoccurs and often worse than before.

So the take away here is that if your lawn has large Oaks and random patches of weak or dead lawn, more than likely it is where one of those large "root" towns or cluster of roots exist.

The work around is to add soil to those areas on a regular basis (yearly) or consider alternate plantings.

Here is a source to a good article about planting under trees: Planting under Trees