If a little is good, much more is better is not a good mantra for mulching. For the overall sense of proper mulching technique, take a cue from Mother Nature. In a forest or natural setting, you’ll commonly see a 2-4 inch layer of fallen leaves, stems, fruits and bark, often referred to as “duff”. Over time, the nutrients in the duff materials decompose, recycling nutrients back to the tree. As much as is feasible, replicate this phenomenon for new plantings. Avoid applying massive depths of mulch or mounding it up on the trunk in a volcano appearance.
Various sources of mulch can be utilized, but in general, natural/organic mulch is best – wood chips, bark chunks, pine needles, cypress, cedar and hardwood. Rock mulches have become popular because of their color and the lesser need for replacement, but they are much harsher on new trees as they add heat and don’t decompose to recycle nutrients.
Weed mats under the mulch are another common but unnecessary material. While allowing water infiltration and oxygen exchange, they usually cause problems with weeds actually growing in the fine pore spaces of the mat. And, as with staking, they require the input of resources. However, on a moderate to severe slope, they can be of some assistance in holding freshly dug soil in place.