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Mulch adds to the beauty and tidiness of a garden. It also enhances growing conditions by protecting the root zones of plants and moderating soil temperatures.

Mulch adds to the beauty and tidiness of a garden. It also enhances growing conditions by protecting the root zones of plants and moderating soil temperatures.

Mulch may make a garden look tidy, but the work it does to improve the growing conditions for plants is what makes it most appealing. Those layers of bark or pine straw also improve soil texture, suppress weeds, and conserve water. In nature, the forest floor is covered by leaves, twigs, fruits, branches, and decomposing plants for much, if not all, of the year. With the help of animals, microbes, and seasonal weather changes, these decomposing materials create a litter layer that protects the soil from erosion and weather extremes. We spread mulch in our gardens to mimic this natural process.


Mulch is any organic substance used as a top cover to soil that enhances the rooting environment of plants. In this context, the term organic refers to substances that readily decompose. While they are often used as soil coverings, materials such as gravel, shell, volcanic rock, limestone, and granite screenings are not actually mulch. These ground coverings do not provide many of the benefits of mulch, such as holding moisture, moderating temperatures, and providing tilth for the soil. Since they retain cold or heat longer, they may keep soil too hot or too cold to benefit plants.

The most common mulches are chipped or shredded bark, chipped tree limbs, or shredded whole trees that are too small for commercial harvest.

Many composted soil amendments, such as mushroom compost, manure, and grass clippings, are also used as mulch. While beneficial in nourishing soil, these materials decompose quickly. Thus, they are not as effective in moderating soil temperatures or retaining moisture unless they are reapplied frequently. Avoid using thick layers of grass clippings as mulch, since they can become a barrier, sealing the soil surface.


Mulching offers many advantages. First, mulches are attractive. They add texture to a landscape and enhance its appearance. This fact alone accounts for much of the widespread popularity of mulching during the past 20 years.

Yet there are even more significant long-term benefits. Properly applied mulch insulates soil and regulates its temperature. In Summer, mulch absorbs the sun’s ultraviolet rays and transforms them into less-powerful, long-wave rays. Heat transfers to the soil through mulch more slowly than if the sun hit the soil directly. In the Autumn, mulched soil loses heat more slowly.

The tempering of soil temperatures has one other benefit for areas subject to frost. Mulch decreases the freeze-and-thaw cycles at the soil’s surface in late winter, and plants suffer less root tearing from the heaving of soil.

Mulch also helps retain soil moisture by reducing evaporation and helping the soil to absorb rainfall. Mulch lessens runoff and potential erosion by eliminating direct contact between soil particles—which are easily dislodged—and raindrops, which can move soil.

While many gardeners use mulch for weed control, mulch simply shrinks the total weed population and makes it easier to pull out any remaining weeds. Most weeds root in the mulch, rather than the soil, and the loose nature of mulch makes weeding easier.

When mulch fails to serve as an effective weed barrier, many gardeners resort to landscape fabrics or sheets of plastic to provide a barrier underneath the mulch. These materials often inhibit the flow of air and water, especially in silty or clayey soils.

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