Are you talking about dead leaf margins on leaves, or something else. If you're talking about leaves, never tear them off because it can damage suppressed buds in the leaf axil (just above where the leaves are attached to the branch). Also, each leaf is a mini food factory working together to provide the plant with its true food - glucose/sugar. The tree has chemical messengers that keep plant central informed insofar as whether or not a leaf is a net user or net producer of energy. When the leaf crosses the line and becomes a liability as opposed to a benefactor, a change in the flow of a growth regulator (auxin) signals the plant to start the leaf shedding process, the first step of which is resorption, during which the plant reclaims mobile nutrients and other compounds for use elsewhere within the plant. The root system needs all the food it can get to reestablish itself in its new digs; so, if you're talking about leaves and not something else, the best approach to take is - if it's green, it stays.
Al
