Washington Township Shade Tree Commission

Mulching

Improper mulching kills trees. Mulch should never be piled into a cone around a tree trunk. This type of mulching is referred to as a "mulch volcano". "Mulch volcanoes" waste money excess mulch and eventually lead to diseased trees.

How should I mulch my trees?

• Start 6 inches from the tree trunk at ground level and mulch outward to the edge of the dripline to a maximum depth of 2 inches to 4 inches.
• Keep a 2-inch to 4-inch layer around, but not touching the base of the tree. Mulch as much of the area under a tree as possible without having mulch touch the trunk.
• Never pile-up a cone of mulch around the tree trunk! Mice, insects, and fungus may hide next to the trunk and feed on parts of the tree. The cone-shaped mulch piles and thick layers of mulch also prevent water from reaching a tree's roots. Tree roots that grow up into the cone of mulch on top of the soil cannot be healthy.
• One layer of woven Landscape Fabric may be used under mulch in heavy weed areas. Never use plastic sheets under the mulch. Plastic sheets block the passage of air and water and stunt root growth.

• Every spring or every other spring, rake or remove any hard crust and add only enough new mulch to maintain a 2-inch to 4-inch layer. Never build up layers of mulch by adding new mulch on top of the old mulch around a tree.

What are the best materials for mulching trees?

• Bark chunks or shredded bark that is at least 3/8 inch in size. Pine bark will last longer than hardwood bark.
• Pine needles
• One-year old wood chips Leaves that were shredded and composted for at least three months

What are the worst material for mulching trees?

• Fresh grass clippings or fresh wood chips
• Any fresh organic mulch
• Any organic mulch that smells bad
• Peat moss or sawdust
• Pebbles, rocks, or cobble stones
• Bricks or pavement or black plastic
• Ground-up rubber tires

Additional Information

• International Society of Arborculture
  • Trees are good
  • Proper Mulching Techniques
• NJ Division of Parks and Forestry
  • Board of Tree Experts