Lawn Sculptors
Mulch can lower the soil temperature by creating an insulative barrier for plants. 3" of mulch can lower the soil temperature by 10 to 12 degrees. It can also prevent erosion and hold in moisture.
Never put mulch against the base of a plant like a tree trunk. Excessive mulching around a plant can hold moisture and could cause the plant to rot.
Turning the mulch every year can help the soil break it down and deliver the nutrients to your plants. Add a little fertilizer to the area to replace some of the nitrogen being used by the microbials that are trying to break down the mulch.