Wood chips are small pieces of wood cut from trees and branches, used mainly for mulch, fuel, and paper production.
Whether you’re spreading them around flower beds or considering them for home heating, the word “wood chips” covers a surprisingly wide range of products. The short version: wood chips are small- to medium-sized pieces of wood formed by cutting or chipping larger pieces like trees, branches, logging residues, stumps, roots, and wood waste. What you plan to do with them determines which kind you should buy, and that’s where most people get tripped up.
How Wood Chips Are Made
Wood chips come from mechanical chipping. Sharp tools cut larger wood into fragments with a defined particle size. Sawmills produce them as a byproduct, tree care crews chip branches on site, and specialized operations chip whole logs.
Bioenergy Europe defines wood chips as “fragments of wood in the form of pieces with a defined particle size produced by mechanical treatment with sharp tools such as knives.” That mechanical process separates wood chips from other products like shredded bark or sawdust, which are made differently and behave differently in use.
What Are Wood Chips Used For?
Wood chips serve four main purposes, and the best choice for you depends entirely on the job.
- Mulch and landscaping: The most common residential use. Chips retain soil moisture, suppress weeds, moderate soil temperature, and control erosion around trees, shrubs, and garden beds.
- Biomass fuel: Chips feed boilers, gasifiers, and industrial energy systems that heat homes, greenhouses, schools, and commercial buildings.
- Paper and engineered wood: Pulp mills turn chips into paper, and manufacturers press them into construction boards and other wood products.
- Animal bedding and playground surfacing: Chips provide absorbent bedding for livestock and a soft, affordable ground cover for play areas.
If you’re ready to buy chips for landscaping, our roundup of the best bagged wood chips breaks down the top-reviewed options by price and coverage.
Wood Chips vs. Mulch: Know Your Grades
Not all wood chips are interchangeable. Fuel-grade chips follow strict standards for size, moisture, and ash content, while landscaping chips have no such requirements.
The most detailed grading system comes from the international standard ISO 17225-4, which classifies fuel chips by quality grade (A1, A2, B1, B2) and particle-size fraction (P16S, P31S, P45S). For example, P16S chips have a main fraction of 3.15 mm to 16 mm, while P45S chips run 3.15 mm to 45 mm.
In practical terms, a smaller boiler with an underfed hearth system needs finer chips at 30% moisture or lower. Freshly chipped wood can run up to 70% moisture, which makes it unusable in many heating systems until it dries.
| Use | Typical Chip Size | Key Requirements |
|---|---|---|
| Garden mulch | 0.5–2.5 inches | No strict specs; any clean wood works |
| Home boiler fuel | 10–50 mm | Below 30% moisture; low ash |
| Graded fuel (ISO 17225-4) | P16S to P45S (3.15–45 mm) | Grade A1–B2; moisture class M10–M35 |
| Paper/pulp | Uniform small pieces | Clean wood, minimal bark |
| Playground surfacing | Varies by supplier | No treated wood or debris |
Common Mistakes To Avoid
The biggest error is assuming any chip works for any job. Fuel systems have strict requirements for size, moisture, and ash content, and mulch-grade chips can clog or damage a boiler. The Wood Heat Association’s guidance on wood chip fuel stresses that the fuel must meet the boiler’s specifications, whatever the raw material.
Moisture is the second trap. Wet chips from a fresh tree can be too heavy and too damp to burn efficiently in a small system. Let them season, or buy from a supplier who reports moisture content.
Contamination is the third issue. Soil and dust raise ash content and reduce fuel quality, so keep chips clean during delivery and storage.
One more expectation to check: wood chips suppress weeds by blocking light and air, but they are not an herbicide. They don’t kill established weeds or plants, so clear the area first.
FAQs
How long do wood chips take to decompose?
Garden wood chips break down over one to three years depending on climate, chip size, and whether they sit on top of the soil or get mixed in. Smaller chips and warm, moist conditions speed decomposition, while larger chips and dry climates slow it down dramatically.
Can I use fresh wood chips around my plants?
What is the difference between wood chips and bark mulch?
Wood chips are cut from the whole tree, including branches and trunk, while bark mulch comes from the outer bark layer. Bark mulch lasts longer and resists washing away, but wood chips hold moisture better in garden beds and cost less per cubic yard in most regions.
References & Sources
- Wood Heat Association (UK). “Wood Chips — Fuel Type Guide.” Details on chip sizes, moisture, and boiler compatibility for fuel-grade wood chips.