There are benefits to ‘mulching’ with both although there are more benefits using the right wood mulch product. Rock or gravel mulch can be the look you are after and is very easily maintained, simply rock or gravel mulch stays in place better. The negatives to rock and gravel mulch is that the gravel does not provide any nutrient value to your plants and the heat absorbed can cause plant burning / stress issues on the hotter days. Wood mulch does provide varying nutrient value to the soil, insulates the soil from heat and cold protecting plants and holds moisture in the soil. Choosing the right mulch for your garden is a very important last step in a successful landscape installation.