Question
I am transplanting a White pine tree, that is approximately 5' tall, and 5 years in age (trunk diameter is 1 1/4")  The tree was planted as a seedling in brown loamy clay.  I am now moving it to an area where the soil conditions are very hard, brown, clay.  The question I have is: Should I undercut the hole that I'm transplanting to, and bring the hole back to the proper depth with better soil?

Answer
Evergreens should be moved earlier in the fall than deciduous plants so they have time to form new roots. They need at least 6 weeks before the ground freezes. In the spring, Evergreens can be planted up to 4 weeks after deciduous trees have opened their leaves, providing that the newly planted trees receive adequate water.

So now is the time to move these trees.
All ages of evergreens, can be successfully moved only if a ball of soil is left around the roots. The exposed roots should be protected with moist burlap or newspaper or with polyethylene sheeting. Every effort should be made to reduce root exposure to wind and sun, keeping the ball as moist as possible. It's best to prepare the hole before digging up the tree you wish to move.

Size of the root ball and size of the hole:

For deciduous trees and shrubs the soil ball should be:

Width = 9-12 in. in diameter/every 1 in. of tree diameter
Depth = 6 in./every 1 in. of tree diameter

For example: A tree trunk 2 inches wide would need a soil ball of 18-24 inches wide and 12 inches deep.

Dig the new hole twice the size of the root ball and as deep. Make sure the sides of the hole since this is heavy clay are not smooth --punch hole in the side to allow water to drain from the hole. Fill with good top soil or potting soil and mulch around the tree with not more than 3 inches deep of organic mulch and water good. I would water every third day for a couple of months if it does not rain then every week for the first growing season.