Mulch. A protective covering, as of bark chips, straw, or plastic sheeting, placed on the ground. In winter, mulch protects bare soil, prevents erosion, and protects in spring, mulch retains moisture, suppresses weeds, and feeds the soil. Mulch — in agriculture and gardening, mulch is a protective cover placed over the soil to retain moisture, reduce erosion, provide nutrients, and suppress weed growth and seed germination. Playsoft playground mulch™ is a natural.