Mulching That Hurts Trees, Mulching That Helps

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“Mulching is one of the most beneficial practices a homeowner can use for better tree health,” reports the International Society of Arboriculture. True. But only when mulching is done right. 

Too often as we work around Howard County and other areas, we see mulching done wrong. It looks neat. It keeps weeds down effectively. But it’s damaging tree health.

Generally the issue is the “mulch volcano,” too much mulch piled directly against the trunk of the tree. Mulch volcanoes–

  • Create a warm moist environment where bacteria that cause bark rot can flourish. This environment also attracts harmful insects such as termites and carpenter ants and provides winter shelter for rodents that chew on bark.
  • Block the proper oxygen-carbon dioxide exchange needed by tree roots. Roots may die back and/or grow up into the mulch instead of down and out as they should. The tree will not be well-anchored. Roots may also grow around the trunk, cutting off the flow of nutrients and water; a “girdled” tree will die if the root wraps all the way around the trunk.

Instead of creating a “volcano” you want to create a “mulch donut” aka “mulch bagel” with mulch set back at 3 to 5 inches from the trunk in the case of a young tree, 8 to 10 inches for a mature tree. You only want the mulch to be 2 to 4 inches deep, even shallower if your soil does not drain well or you are using a fine-textured mulch that slows drainage. Leave the root flare exposed, where the trunk widens. 

While you don’t want your mulch deep, wide is good. Spread the mulch out at least 3 feet out from the trunk, ideally to the edge of the tree canopy or further. Tree roots reach far. In the forest tree roots gain nutrients from the blanket of decomposing leaves, twigs, and bark that surround them. Mulch provides similar support.

Most types of organic material will work as mulch; you can even just use fallen leaves. Undyed wood chips are good (some dyes can leach toxic chemicals into the soil). Many other options exist as well. However, mulch made from rubber, gravel, landscape fabric or other nonorganic material will not provide nutrients; landscape fabric can even block nutrients.

Rake out your mulch if it clumps up; refresh or replace it at least once year as recommended for the type of mulch you choose. Proper mulching is a simple way to gain a wide range of benefits for your tree:

  • More nourishing soil. Research shows young trees that have been mulched will often grow twice as fast as those that have not, given the improved soil nutrients, structure, and aeration that mulching provides.
  • Improved retention of moisture.
  • Decreased competition from weeds.
  • Insulation. Mulch protects against both winter cold and summer heat. Any surface roots will be shielded from sun scald.
  • Protection from human activity. Mulched areas get less foot and vehicle traffic, which compact soil, making it hard for roots to breathe and grow. Mulch also provides a barrier protecting the tree trunk from being damaged by lawnmowers or weed trimmers. This type of damage is one of the top killers of young trees.

Tree Pros does not currently provide mulching services directly. However, we’re always happy to answer your questions on how to best protect and provide for your trees, through mulching and other means.

  

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(410) 771-1717

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