Mulch around trees should be spread over the root area, not heaped up against the trunk. No mulch “volcanoes,” please!
that most trees had “tap roots” that grew straight down.
Along came Cornell University’s Urban Horticulture Institute,
under the leadership of Nina Bassuk, which produced prolific
research about arboriculture, site analysis, and management.
The breakthroughs included that tree roots are mostly in the top
twenty inches of soil and that sixty percent of them reach beyond
the tips of the farthest branches of a mature tree. Bassuk and
her colleagues lectured adamantly to the landscape and nursery
professionals, as well as to extension folks, that the terrible
practice of “volcano mulching” (mounding compost against tree
trunks) must be ended.
Wrong: People dug “hundred dollar holes for ten dollar trees,”
and the holes were very deep. (Sadly, this still happens.) Utility
trenches were dug and construction work was done close to trees,
even within the dripline, cutting off half of a mature tree’s roots.
Workers still tell homeowners, “Oh, it’s all right, lady; those tree
roots are way under where we are digging.” And volcano mulching
is still seen.
Right: A tree should be planted with the root flare (where the
trunk swoops outward into the root system) above ground, not
buried in the soil. You should see that flare at the bottom of all
trees. The hole should be more than three times the width of the
root ball and backfilled with the same soil those roots will have
to grow in. (In the case of depleted or heavy soil, the backfill can
be amended with compost.) The hole should be about the depth
of the root ball (not the very deep hole that was recommended in
old books) so the tree doesn’t sink into a clay basin. And perhaps
three inches of mulch should be spread over the root area, not
touching the trunk!