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Mulching Trees

What is that?

  • Mulching refers to the placement of any material on the ground around plants.

  • Mulches can be divided into organic and inorganic materials.

  • Organic mulches break down over time and become part of the soil, inorganic ones do not.

What good is it?

  • There are so many benefits to mulching trees, it is hard to even count them.

  • Almost all mulches make significant contributions:

  • protect trunk from mowers, weedwhackers, etc.

  • conserve soil moisture

  • impede weed growth

  • reduce soil erosion

  • restrict soil cracking

  • limit salt build-up

  • Most organic mulches add further features:

  • protect the roots from traffic

  • cut down soil compaction

  • improve soil fertility & structure

  • moderate soil temperatures

  • A "green mulch" such as pachysandra or vinca also brings many of these benefits, although it will compete with the tree to some extent for water and nutrients.

  • When possible, do not grow grass beneath trees, especially young trees, because it is highly competetive against them and will restrict their growth.

  • And, oh yes, all mulch looks good.

What problems can mulch cause?

  • Except for needing to be renewed now and then, mulches give very few problems.

  • Avoid fresh organic mulches, i.e., those that have not been leached or composted. They often 1) deplete soil nitrogen, especially if small in size and thickly applied, and 2) can be toxic, especially mulch made of conifer (cedar, for example) sawdust and bark.

  • Many mulches, if put on too thick or against the trunk, actually tend to increase stress, disease and insect troubles, especially on poorly drained clay soils.

  • Geotextile fabrics can lead to higher temperatures, and it is hard to get weeds out of them. If you use them, be sure to cut slits for air and water movement.

  • Black plastic and peat moss should be avoided altogether as tree mulch.

What is the best mulch to use?

  • There is no single best mulch, but organic mulches such as partially composted bark, branches, and leaves are much better for the tree and often cheaper as well.

How do you put it on?

  • To the tree’s dripline, if possible. Remember, the dripline moves out as trees grow.

  • No higher than the heel of your hand. Anything from 2-6" will benefit the tree, though 4" has proven optimal.

  • Not against the trunk. The mulch should look like a donut when you are through.

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