Are Arborist Wood Chips Good Mulch?

Yes, arborist wood chips make an effective landscape mulch. Washington State University Extension's fact sheet on arborist wood chips reports that a layer 4 to 6 inches deep controls weeds, that the common worry about chips stealing nitrogen is a myth, and that over time woody mulch actually increases nutrient levels in the soil. Arborist chips are the mix of wood, bark, and leaves that comes out of a tree crew's chipper, and they are coarser and less uniform than bagged, processed mulch.

Placement matters more than most mulch guides admit. Penn State researchers Davis, Kuhns, Akina, and Harpster, writing in the Journal of Environmental Horticulture in 2004, found that all the wood and bark landscape mulches they studied will eventually support artillery fungus over 3 to 4 years, and that the fungus shoots its sticky spore masses toward light or reflective surfaces. A 1997 Penn State report said those spores can travel as far as 20 feet and stain siding and cars. This guide covers how deep to spread chips, what the research says about nitrogen and disease, where to keep chips away from, and how to use them around trees.

What Are Arborist Wood Chips?

When a tree crew trims or removes a tree, branches and brush go through a chipper. The result is a mix of wood, bark, twigs and, depending on the season, leaves or needles. Brinko Tree Service's brush chipping page describes the same process: branches and brush are processed into wood chips that can be reused as mulch to enrich soil, retain moisture and support plant growth.

Arborist chips differ from bagged mulch in a few ways. They are not dyed, the pieces vary in size, and fresh loads often include green material. Washington State's fact sheet recommends using chips fresh rather than composting them first, because some of the nutrient value, particularly nitrogen from leaves or needles, is lost in the composting process.

Do Wood Chips Rob Nitrogen From the Soil?

Not when they sit on top. Washington State University Extension calls nitrogen tie-up a myth for surface mulch and says research shows woody mulch materials increase nutrient levels in soils or plant foliage over time.

The distinction is where the chips go. Linda Chalker-Scott, the author of the Washington State fact sheet, puts it plainly on the Garden Professors blog: do not mix chips into the soil, but do use them as part of a mulch layer. She adds that chips provide a low, slow feed of nutrients that gradually builds soil.

How Deep Should You Spread Wood Chips?

The two extension recommendations below differ, and the difference is worth knowing:

• Washington State University Extension: 4 to 6 inches of arborist chips controls weeds without detracting from appearance.

• Penn State Extension: 2 to 4 inches of organic mulch and no more, with less on poorly drained soil, and only 1 to 2 inches of finely textured mulch.

The Washington figure is aimed at weed control with coarse arborist chips, while Penn State's guidance covers mulch around landscape trees in general. Around trees, Penn State's range is the safer starting point, especially on poorly drained soil, where it recommends using less. Whichever depth you choose, both sources agree on the most important rule: keep the chips off the trunk. Washington State says to taper the mulch down to nearly nothing as you approach the trunk, and Penn State says to pull mulch 3 to 5 inches away from young trees and 8 to 10 inches away from mature trees.

Can Diseased Wood Chips Spread Problems to Your Trees?

For surface mulch, the evidence says rarely. Washington State University Extension states that most studies indicate diseased mulch cannot transmit pathogens to the roots of healthy trees. The same fact sheet notes that wood chips are not attractive to termites or carpenter ants.

A few pests are exceptions because of how they move. Wood from trees with certain diseases or insects should be handled according to state or extension guidance rather than spread around. Penn State Extension, for example, advises that firewood from oak wilt trees stay at the infection site. If a tree came down because of a specific disease, ask what should happen to its chips and wood before you spread them. Our post on what to do with logs after a tree is removed in PA covers the larger wood.

Where Should You Keep Wood Chips Away From?

Siding, cars, and windows. Artillery fungus, also called shotgun fungus, grows in landscape mulch and fires tiny, sticky black spore masses toward light or reflective objects, according to the 2004 Penn State study. Penn State's 1997 report on the fungus said the spore masses can travel as far as 20 feet and cannot be removed without damaging or staining the surface, and that the fungus caused more than $1 million in homeowner damage claims in Pennsylvania in 1996.

What the researchers found about mulch types:

1. Shredded mulches made mainly of wood, with perhaps 5 to 10 percent bark, supported the most sporulation, because the wood absorbed moisture readily.

2. 100 percent spent mushroom substrate and cypress mulch supported among the least.

3. All wood and bark mulches eventually supported the fungus over 3 to 4 years.

For foundation beds next to light-colored siding or along the driveway, the researchers suggested replacing mulch regularly or, in critical spots, using black plastic covered with stone. Save arborist chips for tree rings, garden paths, play areas and beds farther from the house.

How Should You Use Wood Chips Around Trees?

Spread chips in a wide, flat ring rather than a tall pile. Penn State Extension recommends extending mulch out to the edge of the tree's canopy, called the drip line, and keeping all mulch material away from the trunk. Piling chips against the bark causes the problems Penn State describes with overmulching, including constantly wet bark, root oxygen shortages, and voles chewing the inner bark.

Other good uses include filling in the low spot after a stump is ground, topping off walking paths, and covering bare soil in beds. After a removal, our guides on how to fill a tree hole after stump removal and what to do after tree removal in your yard walk through the next steps, and what happens to tree debris after removal near Pittsburgh explains where the rest of the material goes.

FAQ

Are fresh wood chips bad for plants?

No, as a surface mulch. Washington State University Extension recommends using chips fresh to keep their nutrient value and says the nitrogen tie-up concern is a myth for surface applications.

Do wood chips attract termites?

Washington State University Extension says wood chips are not attractive to termites or carpenter ants.

How far from the house should I use wood chip mulch?

No single distance is set, but Penn State's 1997 report on artillery fungus said its spore masses can travel as far as 20 feet. Keeping wood-based mulch out of beds right against light-colored siding and away from where cars park lowers the risk of stains.

Should I mix wood chips into my garden soil?

No. Linda Chalker-Scott of Washington State University advises on the Garden Professors blog not to mix chips into the soil and to use them as a mulch layer instead.

How long do wood chips last as mulch?

They break down gradually and need topping off. Penn State Extension suggests breaking up matted layers of old mulch with a rake rather than piling fresh mulch on top.

Can I use chips from a diseased tree?

Washington State University Extension says most studies indicate diseased mulch cannot transmit pathogens to the roots of healthy trees. For trees removed because of a regulated pest or a disease like oak wilt, follow the specific extension guidance for that problem.

Brush Chipping and Cleanup From Brinko Tree Service

Brinko Tree Service, based at 1010 Sunset Blvd in Harrison City, has nearly 20 years of experience serving Westmoreland and Allegheny Counties. Its brush chipping service turns branches and brush into wood chips that can be reused as mulch, and its grapple truck service hauls away logs, brush, and debris after trimming, removal, or storm cleanup. Brinko is fully licensed and insured, follows OSHA and ANSI safety regulations with an OSHA safety site supervisor on every job site, and offers free estimates.

Visit Brinko Tree Service or call 412-373-7450 today. Contact us for more information.