Q:
I have a locust tree in my front yard that has such severe surface
roots that it is difficult to mow the grass. I am afraid that the tree
will die if I try to remove the roots. I thought about adding more soil
and reseeding, but I understand that the roots will just grow to the
surface again. I have a maple tree in the back yard with the same
problem. Is there a way to manage this problem without removing the
trees?
A:
You are wise to resist the temptation to cut those roots. They are
important to the health and vitality of a tree. Surface roots are
actually lateral roots that often grow near the surface. They function
in the transport of water and nutrients and are important to anchor the
tree to the ground. Sinker roots -- roots that grow straight down into
the ground -- grow off of lateral roots.
Although certain
species of trees seem to cause more of a problem with surface roots than
others, most large, older trees will produce some surface roots. It is a
common misconception that tree roots grow very deep in the soil. Most
tree roots are found in the top 6 to 18 inches of soil. As the tree
grows in height and diameter, so do the roots, which eventually brings
them to the surface.
Some of the tree
species that are notorious for producing surface roots are those that
grow quickly. These include:
Norway maple (Acer
platanoides); red maple (Acer rubrum); silver maple (Acer
saccharinum); tree-of-heaven (Ailanthus altissima); alder (Alnus
spp.); river birch (Betula nigra); hackberry (Celtis spp.);
American beech (Fagus grandifolia), thornless honeylocust (Gleditsia
triacanthos var. inermis); European larch (Larix decidua);
sweetgum (Liquidambar styraciflua); dawn redwood (Metasequoia
glyptostroboides); mulberry (Morus spp.); Colorado spruce (Picea
pungens); sycamore or London plane tree (Platanus spp.);
poplar (Populus spp.); pin oak (Quercus palustris); black
locust (Robinia pseudoacacia); willow (Salix spp.); elm (Ulmus
spp.) bald cypress (Taxodium distichum); and linden (Tilia
spp.).
Surface roots are common on Silver Maples
Many of these are
trees that tend to tolerate adverse growing conditions. Their propensity
for producing surface roots aids in their survival in such situations.
Environmental factors
play an important role in the growth of surface roots. They are common
when a tree is grown in hard, compacted clay soil or in areas where the
soil is saturated with water frequently. Roots tend to grow where they
find the most favorable conditions: adequate water, air and nutrients.
In poor growing conditions, the most favorable place is often close to
the soil surface. Also, erosion can expose a tree's lateral roots.
Cutting surface roots
can injure and weaken a tree and make it more susceptible to insect and
disease problems that can eventually kill it. Cutting surface roots also
creates a hazardous situation because they serve to support a tree.
Without them, it could fall in high winds or during heavy rains.
Even if you cover
them with soil and reseed the area, those roots will just grow back up
to the soil surface as they continue to grow in diameter. It is not a
good practice to place additional soil over the root system of any tree
because roots need oxygen. If they are buried too deeply, they literally
suffocate, and the tree will decline and die over time.
Finally, running over
those surface roots with a lawn mower is not a good idea. The mower
causes wounds, which can serve as an entrance into the tree for insect
problems and/or disease-causing organisms. Besides, it's hard on the
lawn mower and you!
The simplest solution is
to replace the grass with mulch or a ground cover such as goldenstar (Chrysogonum
virginianum), creeping lily-turf (Liriope spicata), Russian
arborvitae (Microbiota decussata), Allegheny spurge (Pachysandra
procumbens), Japanese spurge (Pachysandra terminalis),
creeping myrtle (Vinca minor), or barren strawberry (Waldsteinia
ternata).
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