"Bill" wrote in message
...

After 35 years I have two large Magnolias about 30 feet high. I
intend to take one down for more light as it blooms too early an burns
due to frost. The other is close and one branch could rub against our
roof. The latter concerns my prune question.

Can I trim it back ?

Good question.
Sure you can. Dose, Timing and Targets play an important role. The
maturity of the trees play a role. I highly suggest that this book be
reviewed. A World Wide Photo Guide by Dr. Shigo.
Also Modern Arboriculture is a great book to address your concerns about
tree health. www.shigoandtrees.com

I have written a section on Pruning and it is he
http://www.treedictionary.com/DICT2003/tree_pruning/

--
Sincerely,
John A. Keslick, Jr.
Consulting Tree Biologist
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.