The answer to 'how often to mulch' is that you should mulch your landscaping 1-2 times per year, typically in the spring and fall. Mulch helps retain moisture in the soil, suppress weeds, and insulate plant roots from temperature extremes. It also gives your garden beds a neat, finished appearance.
The optimal depth for mulch is 2-4 inches. Be sure to spread it evenly around plants, avoiding direct contact with stems and trunks. Over time, the mulch will break down and you'll need to replenish it to maintain the desired depth.