While the terms "wood chips" and "mulch" are sometimes used interchangeably, they're not always the same. Wood chips are often used as a mulching material, but mulch could mean any number of materials beyond wood that work as a mulch atop garden soil. As far as wood-based products used as mulches are concerned, wood chips generally feature chunky pieces of wood, while packages labeled as wood mulch often contain wood that has been shredded and processed a bit more, resulting in thinner pieces.
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Wood Chip Basics
Wood chips, or arborist chips, are the result of tree limbs, branches, and even leaves going through a wood chipper. The exact type of wood in the wood chips depends on the source. In many cases, wood chips are offered for free after a tree is removed in a neighbor's yard or by the city at a local landfill, composting site, or park after the local tree crews empty their chipper bins. Wood chips often contain bits of bark and chunks of wood of varying sizes.
Wood chips make a great mulch for use around shrubs and shrub beds as well as around trees. Apply the chips at a depth of 4 to 6 inches for most uses; the chips will settle a bit within a couple of weeks. As the chips break down, they release nutrients into the soil, offering a beneficial boost to any plants nearby. Wood chip mulch also suppresses weeds for a while and helps keep moisture in the soil from evaporating too quickly.
Mulch Basics: Wood and Beyond
Wood mulch, which also started out as some form of wood run through a chipper, is often sold in bags at garden centers. Shredded mulch isn't always from tree-trimming projects, however; the mulch may come from shredded pallets or byproducts of other wood-consuming industries. The wood in bagged wood mulch tends to be a bit stringier than loose wood chips due to the mulch wood being ground a second time for a finer product. Wood mulch is often dyed brown, reddish, or black, which gives the flower beds a uniform appearance once the mulch is in place.
Specific wood mulches are also available from some suppliers, such as hemlock mulch containing only hemlock wood or bark mulch made from ground assorted tree bark. The product information usually specifies which woods are used for the mulch or whether the mulch contains dye.
Mulch doesn't have to be made of shredded wood. It could be made of other organic materials, such as the shells of cocoa beans or hazelnuts, pine needles, or straw, and from completely inorganic matter, such as stones or recycled rubber. Inorganic mulches don't break down much over time and don't add nutrients to the soil, but they do keep weeds at bay, and they help insulate the soil.