The following is information on mulching for landscapers to consider.
After planting, mulch immediately with organic materials that slowly release nutrients and improve soil quality as they break down. Mulch moderates soil temperatures,reduces water needs and helps prevent weeds and erosion. Mulch also eliminates damage from string trimmers and lawn mowers.
• Apply mulch 2-4 inches deep and extend it past the drip line of plants. To prevent disease and insect damage, pull mulch away from the plant stem or trunk.
• Do not use plastic under mulch. Plastic film severely limits water and oxygen movement to plant roots. Landscape fabrics may be used, but weed and grass seeds that blow onto the fabric and root through it make removal difficult.
• Suitable mulches include softwood bark, pine straw, bark nuggets, bark mini-nuggets, shredded leaves, hardwood bark, and root mulch.
• Avoid heavy applications of grass clippings, which mat and repel water. Wood chips should be aged since fresh chips may release toxic substances into the soil and absorb nitrogen in the break-down process.
• Grouping plants together in a mulched bed instead of planting in individual holes keeps larger root areas cool and moist, providing better conditions for plant growth. It’s also easier to mow around large areas than small ones.
Information from "Environmentally Friendly Landscape Practices" By Robert R. Westerfield, Extension Horticulturist and Daryl Pulis, Master Gardener Advanced Training Coordinator, University of Georgia http://pubs.caes.uga.edu/caespubs/pubs/PDF/C967.pdf