The answer to 'how often to mulching' is that most experts recommend applying a fresh layer of mulch around your plants and trees once or twice per year. Mulch helps retain moisture in the soil, suppress weeds, and insulate plant roots from temperature extremes.
In the spring, apply a 2-4 inch layer of mulch around the base of plants, trees, and shrubs. Reapply in the fall to replenish the mulch that has broken down over the summer. Be sure to keep the mulch a few inches away from the stems and trunks to prevent rot.