I live in Wausau, Wisconsin. Our city planted small
maples two years ago near the street. They are now about 8-10 feet
tall. Both of ours show some encircling roots above the surface of
the ground under the mulch. The roots are about 1/2 inch diameter in one case
and a bit larger in the other. Is it too late to prune these
away? Any other suggestions?
The answer to your question will depend, to some extent, on the
type of maple tree you are growing. Silver maple will tolerate
root-pruning, but sugar maples are intolerant of it, and can be
more likely to break in windstorms if roots are pruned. There is
always some risk of loss involved in root-pruning a tree.
Source: Iowa State Extension.
Since encircling roots are not good for the tree, you probably will
need to prune, but it would be best to consult a certified arborist
in your area to make sure this is done correctly. University of Minnesota
has a guide (now archived) called “Stem Girdling Roots: The Undergound Epidemic Killing Our Trees” by Gary Johnson. Excerpt:
Removal is the most common treatment of encircling roots or SGRs
that have caused minimal stem compression. Roots may be removed
with wood gouges, saws, or pruners during the examination process.
When SGRs have caused extensive stem compression and are fully or
partially embedded in the stem, modify the removal treatment to
avoid damage to the stem. Embedded and severely compressing SGRs
are often left in place when they cannot be safely removed; there
is some belief that SGRs reduce the typically short life span of
urban trees by only a few years, and the potential damage
associated with SGR removal is not justified (Watson et al. 1990;
Tate 1981). A compromise is to prevent the SGR from growing and
further compressing stem tissues by severing it at the edges of the
stem. Remove the remaining root to a distance where it no longer
poses a threat to the stem and allow the severed SGR to decay with
time. Annual examination of the stem to assess for decay is
recommended.
The season during which SGRs are removed might influence the
success of the treatment. Smiley (1999a) found that summer removal
resulted in better diameter growth over two years than did fall
removal or a combination of summer and fall removal for red maple
trees under an irrigation system.
Regardless of treatment, do not backfill the examination area.
Lightly mulch the exposed roots but not the root collar flare or
stem area. Subsequent examinations will not require the
time-consuming removal of soil.
To find a certified arborist in your area, you can search your
local chapter of the International Society of Arboriculture.