Soil
Mulch
Mulch is a layer of material, often wood chips or bark, spread over soil to hold moisture, slow weeds and keep the ground cooler in summer.
Mulch is a covering spread over bare soil. Organic mulches such as bark, shredded wood and wood chips break down slowly and add organic matter. Iowa State Extension says organic mulches serve several important functions in gardens and landscape plantings.
Clean wood chips from a grinding job can work as mulch in a bed or around a tree. They should not stay in the hole where grass will grow, because wood in the soil can cause nitrogen tie-up. Use them on top of the soil, not mixed in.
Keep mulch a few inches away from living trunks. See can I use stump grindings as mulch and what to do with stump grindings.