I came across this just now, thought maybe it would be helpful to anyone having issues with root bound plants.
"I had known how to direct the roots away from the plant using a root hook, or by scoring the sides of the roots with a sharp blade. However, what I did not realize was that root bound plants often become so dense, they will not absorb water. The density of tangled roots in a container plant can make the plant hydrophobic—it literally sheds water."
LINK: http://landscapeofmeaning.blogspot.com/2011/06/best-planting-tip-i-ever-received.html
"I had known how to direct the roots away from the plant using a root hook, or by scoring the sides of the roots with a sharp blade. However, what I did not realize was that root bound plants often become so dense, they will not absorb water. The density of tangled roots in a container plant can make the plant hydrophobic—it literally sheds water."
LINK: http://landscapeofmeaning.blogspot.com/2011/06/best-planting-tip-i-ever-received.html