Why should you place mulch around your trees?
Helps reduce soil moisture lost through evaporation
Reduces the potential harm from weed whackers and/or lawn mowers
Can improve soil structure as mulch decomposes over time
Helps control weed germination and growth
Reduces soil compaction
Enhance biodiversity and beneficial organisms
Insulates soil, protecting roots from extreme summer and winter temperatures
Gives planting beds a uniform, well-cared-for look

Best mulching practices!
By placing mulch around the root zone of a tree you reap the benefits of healthier plants and soils. As beneficial as mulch is, too much can be harmful. On wet soils, deep mulch can lead to excess moisture in the root zone, which can stress the plant and cause root rot, just to name one danger. The generally recommended mulching depth is 2 to 4 inches.
First, determine whether the soil drainage is adequate. For well-drained sites, apply a 2 to 4-inch layer of mulch (less if poorly drained). Coarse mulches can be applied slightly deeper without harm. Place mulch out to the edge of a tree’s crown or beyond. If mulch is piled against the tree trunk, pull it back a bit so that the base of the trunk is exposed.