Question
From your forum: http://en.allexperts.com/q/Trees-739/2009/4/PRUNING-
JAPANESE-MAPLE.htm

When is the best and safest time to prune a japanese maple?  

A second question on a regular maple tree:
Greenville, SC.

I have a 10-12 year old Maple tree in my back yard.  It has two trunks that
rise about 20 feet, and split apart from each other at about 20 degrees.  One
is slightly taller and more vertical than the other, and I am thinking these are
co-dominant leaders (yes - I am armed with a pruning book).  I would like
the tree to grow taller, and I am thinking the smaller leader should be cut off.  
I have a couple of questions regarding this:

Should I cut off this second leader, which will remove a significant portion of
the tree, and if yes, then when should I cut off this leader?  Or should I just
shorten the second leader, and if so, when?


the larger leader has a diameter of 11.5  inches at the point where the two
are joined.  A foot up from that, this larger leader is only 9 inches in diameter
and round after its first branch.  At the 11.5 inch point, the leader is not
round - but more like two round branches slowly growing out of each other

the smaller leader has a diameter of 12  inches at the point where the two are
joined.  A foot up from that,  this smaller leader is then 7.5 inches in diameter
and round, after its first branch comes off.  This second leader angles more
outward, and it is not as tall as what I consider the larger leader.  The 12 inch
section is not round either (same as what I described above).

The bark where they are joined has what looks like a black fault line between
them.  In fact, this seems to be the case where the leaders have branches
coming off of them.  All of the branches in this area seem to be about 20 to
30 degrees.

I can post a picture if this is confusing.

I am pretty sure I can tackle this job.

Thanks,

Ted  

Answer
Fall and winter is a common time to prune and shape deciduous trees and shrubs . Exceptions to this are maples which will bleed or ooze sap unless pruned when in leaf.   When maples are pruned in late winter or early spring the wounds flow with sap. If heavy sap flow occurs, pruning should be delayed until midsummer. This flow of sap can lead to disease invasion and weakening of the tree.   The preferred time to prune maples is between mid-July and August, a period when sap won't run from cuts.   The one time when trees should not be pruned is during early spring when buds are breaking during leaf expansion.   Maples should be given a thorough pruning every three years and minor "touch up" pruning annually.   A thorough pruning involves removing dead limbs, crossing branches (or branches that will cross in the future).

Give newly planted trees and shrubs only minimal pruning. Removing too much top affects the production of food energy (carbohydrates) and can result in poor root development. After planting, prune out broken branches and those with weak or narrow crotches. With young trees, leave some of the lower limbs and sprouts even though they will be removed later. These limbs provide the closest source of food energy for root development.

My first thought about the forked maple is leave it alone. But a picture would help give a better idea of what is involved. Removing the fork will not make the tree any taller but will make the crown  lopsided. Since the "branches" are this large I lean toward doing nothing.