The adage that nature abhors a vacuum rings true in a healthy forest, where plant, animal, and microbial life fill every niche from the ground up. It’s a rich, well-regulated biome that is very beneficial to the growth and longevity of trees. 

The soil is enriched by the understory-dwelling creatures that recycle nutrients, and the temperature and moisture level of the soil are regulated by the canopy’s shade.

By contrast, urban and suburban biomes seem pretty bare, with oases of plants amid deserts of homogenous turfgrass. Here, excess sunlight dries and overheats the soil, which is of poorer quality without the fertile, decaying litter found on the forest floor.

Applying mulch—an insulating, nutritious layer of organic material—is one way to help your trees thrive outside of the forest. Keep reading to find out more about the benefits of mulching around trees as well as the method for properly spreading organic mulch.

Why mulch?

Mulch is a manmade analog of humus, organic matter that has been broken down by earthworms, fungi, and other organisms that aid the process of decomposition. 

The makeup of manmade mulch is much simpler than what occurs naturally in the forest, but layers of material like pine straw or bark chips will still effectively regulate soil temperature and help retain moisture.

A broad mulched area over a tree’s root system also protects against both weed growth and injury from lawn mowers and weed whackers.

Store-Bought Mulch and Homemade Compost

For trees, horticulturists recommend organic mulches over inorganic mulches made of rock or plastic sheeting, which insulate roots effectively but cannot provide nutrients or help aerate the soil.

At the store, it’s easy to find organic mulch materials, including pine bark, pine straw, and wood chips. You can research which mulch is best for your particular breed of tree, but keep in mind that most trees can benefit from a diverse array of materials.

Enterprising homeowners can also make compost for use as mulch.

Noting that yard waste accounts for nearly 17 percent of the solid waste in municipal landfills, the EPA suggests composting fresh lawn trimmings (green materials) by mixing them with an equal amount of dead leaves, pine straw, and coffee grounds (brown materials).

Periodically adding moisture and turning the mixture encourages the growth of microbes that break down the material. After a few days to a few months, depending on the ingredients in your concoction, the compost should be ripe and ready to serve as mulch for your trees.

For more detailed composting instructions, the EPA recommends the resources provided by the Waste Management Institute at Cornell University.

How to Apply Mulch

You can apply mulch at any time of the year, but it’s best to do it in late spring, after the milder spring sun has warmed the soil and before the summer heat has had a chance to dry it out.

  • To begin, look at the drainage properties of the areas you want to mulch. Apply two to four inches of mulch if the site is well drained, or spread the material more thinly if the soil tends to stay moist.
  • Don’t pile mulch around the tree trunk; instead, spread the mulch in a ring that begins a few inches away from the base of the tree and radiates out to the drip line, the circumference created by the tree’s outermost branches.
  • Organic mulch decomposes and must be renewed at a rate that depends on the kind of mulch as well as the environmental and soil conditions. Pine straw mulch will likely need to be replenished once a year, while pine bark may provide good root insulation for several years. Keep an eye on your mulch and add a one-inch layer as needed.

Mulch is a simple and effective way to improve the soil conditions around your trees. Follow these steps to apply mulch properly, and consult a tree care specialist for help developing a comprehensive program for maintaining your trees’ health all year long.

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