Mulch is truly a gardener's friend. It helps reduce weeds, retain soil moisture, moderate soil temperatures, and replenish soil nutrients-not to mention how it dresses up the garden. Any organic mulch will work well in your perennial beds, including shredded bark or leaves, cocoa bean hulls, and pine needles.
You may want to stay away from wood chips in a perennial bed. Their coarse texture can overwhelm perennials, and the larger chips tie up nitrogen in the soil as they decompose. Also, keep the mulch a few inches from your foundation to deprive small rodents of a place to call home. Leave a gap of 6-12 inches from the foundation if you use wood-based mulch. This will prevent termites from having direct access. Whatever mulch you use, be sure to put down a layer 2-4 inches thick. If you use less than that, weeds may still grow through it; if you use too much mulch, you may restrict the amount of oxygen getting to the plants' roots. Replenish mulch every year or two as it decomposes.