Mulch is anything that will facilitate the improvement of the micro
organisms in the soil. Much has been misleading in mulch applications. I
would like to set some straight. First let us focus on trees. Anything
with the word FRESH in front of it is NOT GOOD. The relationship fresh
material has with the soil leaves us with the statement: "letting these
materials sit for at least one year is best." That is fresh chips, fresh
manure and so on. After one year, these things are fine in the right
amounts to be used as mulch. Tree trimmings are very good if applied after
they have sat for at least one year. Some places sell so called "mulch"
that is nothing more than just painted fresh chips (Not all). Mulch is too
thick when roots start growing into it. When roots are growing in the
mulch, several continuous hot dry days can lead to root death. Mulch is
very beneficial for trees. Start by applying 3 to 4 inches(7 to 10 cm.) and
inspect the mulch several times a year for root growth. Keep mulch at least
6 inches(15 cm.) away from the trunk to reduce chances of rodent injury and
infection by pathogens. Excessive amounts of mulch may disrupt soil
moisture and aeration. It is best to keep adding small amounts of composted
material over time. The latter are clips from 100 TREE MYTHS by DR. ALEX L.
SHIGO

Mulch "should" extend to the drip line and placing it on top of the grass
(FLAT) rather then removing the grass is better. We can do more damage by
removing the grass now that it is there. We are over grassed as a nation
and grass will kill a tree. Only extending the much out to four feet surly
is better than no mulch at all! If we take "dead" wood out of your trees,
we can chip it up and place it right back around your trees. Fallen leaves
are great mulch. Bark mulch should be avoided.
For much more on the topic:
http://www.treedictionary.com/DICT2003/M/mulch.html

--
Sincerely,
John A. Keslick, Jr.
Consulting Arborist
http://home.ccil.org/~treeman
and www.treedictionary.com
Beware of so-called tree experts who do not understand tree biology.
Storms, fires, floods, earthquakes, and volcanic eruptions keep reminding us
that we are not the boss.