The Homeowners Column

The Homeowners Column

Mulching Trees

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

Mulching trees isn't particularly new and innovative. Mother Nature has been doing it for years in the forest. Most of our landscape trees in their native forest areas are naturally mulched by leaf litter and plant debris. The growth and health of landscape trees can be dramatically improved by the use of mulches.

Mulches are any materials used on the surface of the soil. This broad definition includes organic materials such as wood chips, pine needles, straw, peat moss, corn cobs and lawn clippings. Inorganic mulches include river rock, ground tires, volcanic rock and synthetic fabrics.

Generally, organic mulches are preferred for plant growth because of their ability to improve soil structure and provide a more natural environment for good root growth and, therefore, good top growth of the plant or tree.

Benefits of organic mulches include:

  • Conserving soil moisture. Mulches can also increase water penetration into the soil.

  • Maintaining a uniform soil temperature by insulating the soil. Mulches keep the soil warmer during cool weather and cooler during warm weather.

  • Minimizing soil erosion and compaction from rains, lawn mowers, and people.

  • Improving soil structure through the decomposition of organic mulches. This is particularly important in heavy soil types. Mulches keep clay soil from cracking after rains. Mulches encourage worm activity and other beneficial life in the soil.

  • Reducing weed problems by preventing weed seed germination. First, make sure the mulch comes in free of weed seeds.

  • Giving a neater, more finished look to landscape areas.

  • Keeping lawn mowers and string trimmers away from tree trunks and surface roots. Few things will bring a horticulturist to tears faster than to look at what would be a beautiful tree specimen only to see trunk damage due to lawn mower blight. Once a tree is damaged from lawn mowers scrapping the trunk or string trimmers bruising the trunk, little can be done to correct the damage. However, damage is easily prevented with the use of mulch.

Some disadvantages of organic mulches include:

  • Fresh materials could cause nitrogen deficiency as they decompose, if fertilizer is not added regularly. Fresh mulch should be composted for at least three months before use.

  • Fine-textured mulches such as sawdust or grass clippings may retain too much moisture, so should be applied in several thin layers or mixed with a coarser material. Generally mulches such as pine needles and oak leaves are not going to cause dramatic changes in the acidity or alkalinity of the soil as is often believed. Oak leaves, for instance, may be acidic when fresh, but as they decompose the alkaline reaction raises the pH.

Mulching recommendations around trees:

  • An organic mulch such as wood chips or compost is preferable to an inorganic mulch such as rock.

  • Apply composted material to the soil surface and top with coarser and fresher material. Incorporation into the soil is not recommended or necessary.

  • Mulch should be about four inches deep. Do not exceed six inches in depth.

  • The larger the mulched area the better, but it should reach at least to the tree's drip line (the outer perimeter of the branches).

  • Keep mulch at least 6 inches away from the tree trunk.

  • Apply mulch after a hard frost in fall or after frost in spring

  • Avoid disrupting the mulch with annual flowers. If plants are desired, use perennial ground covers such as vinca or English ivy.

Check out the Landscape Recycling Center at 1210 East University Avenue in Urbana. They have a great selection called woodland mulch. They even deliver for a small fee. Call 344-5323.

Trees are an important part of our landscapes and communities and proper tree care should include mulching.

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