I never consciously place symbolism in my writing. That would be a self-conscious exercise and self-consciousness is defeating to any creative act. Better to get the subconscious to do the work for you, and get out of the way. The best symbolism is always unsuspected and natural. During a lifetime, one saves up information which collects itself around centers in the mind; these automatically become symbols on a subliminal level and need only be summoned in the heat of writing.