I looked at your web site. What is the radius of the mulching area.

OK, you could mulch you whole yard if you like. But really, you could mulch
to the drip line. Beware that small amounts of mulch properly applied can
make a big difference. In Hawaii they mulch to the drip lines because they
have to recycle all that material because they have no room to establish a
land fill. I start my applying about 4' wide circle around the tree. Again
for more specific suggestions go here -

Mulching - http://home.ccil.org/~treeman/sub3.html
and
http://www.treedictionary.com/DICT2003/M/ Look up "Mulch"


My trees are mulched, but I don't know if they are "correctly"
mulched.

Keep mulch back at least 6" from the base of the tree or trunk flair. 3-4"
thick and flat.


For the sodded area, I have 2 trees that are mulched. In my back yard
(non sodded), I have about a dozen trees. Should I mulch them as
well?

I would. But do not dig out the turf because the turf roots grow deeper
than the absorbing non-woody roots of the trees. If we dig out the turf
roots we remove the tree absorbing roots. Just cut the turf low and place
mulch on top.


You say it could effect the absorbing process of the trees. In what
way would it effect them?

Example is pin oaks. They require acidic soil. By raising the pH we tie up
certain elements such as iron. I did some soil research in old growth
forest and found that eastern hemlocks like a pH of 4.5. Depending on your
tree species the pH requirement will vary. I would hate to see your turf to
well and the trees die.
I would think if you gave your trees a mulched area it would help.

I would suggest something like this: http://home.ccil.org/~treeman/mul2.html

I do not have all the answers, however if there is anything I can do to help
you, I will.

I would then keep the lime application back from the mulch.


Sincerely,
John A. Keslick, Jr.
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.