Georgia Gardener Newsletter Design Tip: January 22, 2009
Surface Roots of Trees
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Surface & Girdling Roots on Sycamore
Hardly a week goes by that I don't get a call or email about tree roots surfacing in lawns or pushing against driveways,
sidewalks and foundations. The problem usually stems from a lack of knowledge about tree structure especially the growth that
occurs below the ground: the roots.
Here are some root facts...
Tree roots need air. The depth of tree roots is dependent upon the amount of oxygen in the soil. Remember these three numbers:
15-5-2. Healthy tree roots will grow in soil where the oxygen content is 15%. Root growth stops when the oxygen level drops
to 5% and roots die when the oxygen level is 2% or lower. When you have heavy soils such as compacted clay, the oxygen
levels drop off rather quickly versus looser soils such as sand. Therefore the less pore space in the soil, the lower the
oxygen levels, the closer the roots must remain to the surface.
- Most roots are contained in the top 12-24 inches of soil - even on very large trees.
- The absorbing roots are usually found in the top 8-12 inches of soil.
- Mature trees rarely have taproots.
- Tree roots can extend as much as 2-3 times the distance of the canopy.
Even in good soils, some trees just seem to naturally have roots that run on top. The worst offenders I've observed are: maple,
river birch, cherry, sycamore, southern magnolia and some oaks.
Dos and Don'ts
When dealing with a tree root that has surfaced in the lawn or flower bed, the first inclination is to put more dirt down
and be done with it. Most trees resent having their roots buried even by just a few inches (that oxygen thing again)
and will either show stress or
almost seemingly "pick their feet" up so that the roots are back on top. If you push the issue too far, you could end up
with a dead tree.
- Enlarge the bed or island around the tree so that the surface roots are not in turf areas.
- Cover the surface roots with 2-3 inches of organic mulch: pine straw, shredded leaves, etc.
- Cover the roots with only 1-2 inches of very good quality topsoil.
- Make sure the root flare is visible.
- Plant trees in large open areas away from structures.
- Bury the surface roots with several inches of soil.
- Cut/remove larger surface roots.
- Hide the roots by building a raised flower bed or box.
The root flare where the trunk meets the roots
A clever way to avoid root & sidewalk damage
If you have a tree that is starting to damage a sidewalk, driveway, retaining wall or foundation, DO NOT take it upon
yourself to do some root pruning. Imagine what would happen if you decided to remove a leg or two from your kitchen
table. Roots not only provide nutrients to the tree, they are paramount to the tree's stability. Always consult
with a Certified Arborist before doing major root disturbance.
And finally ... If a tree is on your neighbor's property, you have the right to prune any part that
crosses the plane of your property line. However when it comes to roots, if you destabilize a tree by cutting them you
could be responsible should something happen. Do the neighborly thing and consult with your neighbor and a Certified Arborist
about the best way to proceed.
To find a Certified Arborist, visit the web site of the
Georgia Arborist Association.
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