Over time, perhaps 2 to 5 years depending on the variety and age of your maple, it will be necessary to replace the exhausted soil in the container and revitalize the root system with root pruning. Timing is probably the single most important criteria to a successful root pruning. During dormancy, about 2 to 3 weeks prior to bud break is the ideal time. During this period there is active root growth and no demand on the root system from the tree. If your not sue when emergence is in your area watch for a slight swelling and shininess of the buds.