Guide
Free Arborist Wood Chips as Mulch
The short answer
Yes, fresh arborist wood chips are safe to use as mulch, and Washington State University Extension rates them among the best mulches for trees and shrubs. The famous fear (that chips 'rob nitrogen' from your soil) applies to wood incorporated INTO soil, not wood laid on top of it. As WSU's Linda Chalker-Scott summarizes the research: wood chips will not draw nitrogen from the soil unless they are incorporated into it, and as a surface mulch they actually increase soil nutrient levels over time as they break down.
The honest caveats are few: don't dig chips into beds; be cautious using deep chips over shallow-rooted annuals and vegetables, where the narrow nitrogen-poor zone right at the mulch-soil interface can matter to seedlings; and keep chips pulled back from trunks and stems. Everywhere else (trees, shrubs, perennial borders, paths), a free arborist load spread around four inches deep suppresses weeds, holds moisture, and feeds the soil.
The nitrogen tie-up myth vs the surface-mulch reality
The myth has a true core: fresh wood is high-carbon, and soil microbes decomposing wood mixed through soil borrow nitrogen to do it, temporarily starving plant roots in that soil. That is why you never till chips or sawdust into a bed. But mulch sits on top. Decomposition happens only in the thin film where chips meet soil, and research reviewed by Chalker-Scott shows woody surface mulches leave underlying soil nitrogen unchanged or, over time, increased as the chips decompose into nutrients and organic matter.
The thin nitrogen-depleted zone at the interface even works for you: it is one reason weed seeds struggle to establish through a chip mulch. Established trees, shrubs, and perennials, whose roots run deep and wide below that interface, are unaffected. This is not a fringe view; it is WSU Extension's published position, echoed by UC agriculture and natural resources horticulturists.
Where arborist chips shine
Around trees and shrubs, over perennial and mixed borders, under hedges, and on paths, arborist chips are close to ideal: free, heavy enough not to blow away, slow to break down, weed-suppressing at depth, and moisture-conserving. Their mixed composition (bark, wood, and leaves in varied sizes) is an advantage over uniform bagged mulch, decomposing at varied rates and feeding a broader soil community.
Fresh is fine. Chalker-Scott's guidance is to use chips soon after chipping to get the most nutrient value; you do not need to age or compost them first for landscape use. Spread them at least four inches deep for reliable weed suppression, and top up as they slump.
- Best uses: trees, shrubs, hedges, perennial borders, paths
- Depth: around 4 inches for weed suppression; top up yearly
- Fresh chips are fine as surface mulch; no need to age them
- Free sources: local tree services and arborist chip-drop programs
Where NOT to use them
Don't incorporate them. Digging or tilling fresh chips into soil is the one scenario where nitrogen tie-up genuinely bites; if chips end up mixed into a bed, expect to add nitrogen to compensate.
Be cautious in annual and vegetable beds. Seedlings and shallow-rooted annuals live exactly where the interface nitrogen dip occurs, and beds that get dug over each season will mix chips in. Use compost, straw, or finer mulches there, and save the chips for permanent plantings and paths.
Keep chips off trunks and crowns. Piling mulch against bark ('volcano mulching') holds moisture on the trunk and invites rot and rodents; leave a clear ring around trees, shrubs, and perennial crowns. And on slopes above drains, remember chips can float in a downpour.
⚠ Never dig fresh wood chips into a bed you plant this year. On top: fine. Mixed in: temporary nitrogen drought for your plants.
Getting free chips
Tree services pay to dump chips, so many will happily drop a load at your house free; call local arborists or use a chip-drop matching service. The loads are big (often several cubic yards), arrive unscreened, and may mix species and leaf content, none of which matters for landscape mulch.
If a load sits in a pile for months, the interior composts and heats; that is harmless, and stockpiling has even been shown to reduce plant pathogens in chips from diseased trees. For the full mulch decision (chips vs bark vs compost vs stone vs rubber), see our mulching guide and our rubber and dyed mulch safety page.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- WSU Extension — Using Arborist Wood Chips as a Landscape Mulch (FS160E, Chalker-Scott) — Arborist wood chips are an excellent landscape mulch; woody surface mulches do not deplete underlying soil nitrogen and over time increase soil nutrient levels; a thin nitrogen-deficient zone at the mulch-soil interface likely helps inhibit weed seed germination; caution advised with shallow-rooted annuals and vegetables; do not incorporate chips into soil.
- UC ANR — Myths of Mulch (Topics in Subtropics, citing Chalker-Scott and Downer) — Wood chips will not draw nitrogen from the soil unless they are incorporated into it; chips are best applied soon after chipping; maintain a depth of at least 4 inches to prevent weed growth; stockpiling chips reduces plant pathogens.