Wood Chip Mulch

Wood Chip Mulch

Wood Chip Mulch

What is your favorite mulch material?  There are so many options that it can become confusing.  Did you know that there is a body of scholarly research just on mulch?  Neither did I until I started doing a little research.

I started researching wood chip mulch primarily because I wanted to see if there was any scientific evidence to back up the incidental evidence I have gathered.  I have been recommending wood chip mulch for a while.  I always like to have science on my side when I start making recommendations, so the research commenced.

I did find a lot of research on mulch.  Much of it is aimed at commercial agriculture production, and many times this research is centered around a specific crop or plant.  The research is good and interesting to read (if you like reading research papers) and much of it can be applied to home and hobby gardening.  I was gratified to find that there is also a substantial amount of research comparing the various forms and types of mulch that are commercially available.

First things First.

I always have to begin at the beginning and that always starts with “why mulch?”  Let’s take a quick look at the benefits.

Mulching can:

  • Improve soil structure
  • Enhance Water Infiltration and Retention
  • Prevent erosion and compaction of the soil
  • Moderate soil temperature.
  • Provides Nutrients
  • Suppress pathogens and pests
  • Supports beneficial organisms
  • Neutralizes pollutants

Why Wood Chips?

Free stuff is good

A 1990 study of 15 organic materials used as mulch found that wood chips were one of the best performers in almost every category studied.  Wood chip mulch excelled at moisture retention, temperature moderation, weed control, and sustainability.  I consider all of these to be priority items when selecting a mulch for West Texas, where water retention and soil temperature can be one of the biggest challenges. (Stinson, Brinen, McConnell, & Black, 1990)

wood chip mulch with green material

 I also wood toss economics into this mix.  It wasn’t part of the study, but it is always a concern for home gardeners.  In many urban areas, wood chips can be sourced for free with a little work.   In our area, the city solid waster department makes wood chip mulch available for free if you can pick it up and load it.  Companies that trim trees for local utilities will often make a load of fresh wood chip available for free if you have a place they can dump their truck.  Free is good!

What makes it superior?

Many commercially available mulches are often quite uniform in size and shape.  This makes these materials tend to compact and nest tightly together.  Other materials, such as grass clipping and leaves suffer from the same sort of problems.  Wood chip mulch, especially locally sourced as mentioned above, contains heartwood, bark, leaves, twigs, and limbs.  This diversity of size and material makes wood chip mulch a better choice for several reasons

  • The diversity of shape and materials makes wood chip mulch less likely to compact.
  • Diverse materials decompose at different rates which creates a much richer and more diverse environment, leading to healthier soil biome.
  • Wood chips tend to decompose slower than other materials.  Slower decomposition makes the sustainability of the mulch layer longer leading to less work and less replenishment over time.
  • Slower decomposition releases nutrients slower into the soil system, keeping them closer to where they are needed rather than leaching out rapidly.
  • Wood chips showed superior water retention capabilities to most other mulches in the study. 
  • Weed suppression was better with wood chips than most of the other materials tested.

The best way to use wood chip mulch

Wood chip mulch can be used in many ways in the garden and landscape.  The most obvious and most used is to mulch garden beds around plants and trees.  When using wood chip mulch for this purpose, there are a few things you should add to the mix.

  • Use the wood chips fresh.  The nutrient values are at their highest just after the material is chipped.   The longer it sits and ages, the more the nutrient value drops.  Don’t misunderstand.  Even older wood chips that have aged a bit are still a superior choice, but there is no reason to wait.
  • Sandwich your mulch.  Add a layer of good quality compost on top of your garden or landscape soil before laying down your mulch.  To add a bigger punch, sprinkle worm castings and dry molasses on the compost and then spread a nice layer of mulch over that.  The worm castings are loaded with microorganisms, and the molasses will give those bacteria and fungi a kick start under the mulch.
  • Mulch all your bare soil.  Nature abhors bare soil and weeds will appear first where there is no cover on the soil.  Mulching bare soil helps to keep it healthy, prevents weeds, and starts to build the microbiome in that soil.
  • Mulching can be an effective way to eliminate grasses in areas where you want to establish new grow beds.   Lay down a thick layer of brown cardboard before you mulch.  It isn’t necessary to remove the grass.   The thick layer of cardboard will stop any light from reaching the grass, especially Bermuda grass and the mulch will hold the cardboard in place as it begins to decompose.  In a short time, the grass beneath the cardboard will be dead, the cardboard will have decomposed, and the mulch will be doing its job on the surface.
  • Maintain your mulch.  By its very nature, wood chip mulch requires replenishment.  As the lower layers begin to decompose, the upper layers will also start to break down into smaller and smaller pieces.  The thickness of the mulch will diminish over time and should be refreshed.  I like to maintain a 4 to 6-inch layer of mulch all the time.  Where I am using mulch for walkways or paths, I often increase that depth to 8 to 12 inches.  Foot traffic on wood chip mulch speeds up the decomposition process.
  • Don’t mulch up to the base of your trees.  Piling mulch against the lower portion of your trees can cause an anaerobic environment which can lead to disease, fungi, and rot.  Many boring insects also love the shelter that mulch can provide if it is piled against a tree.  Rather than piling the mulch in a volcano shape against your tree, switch to a donut shape leaving a space around the root flare of the tree.

Much of the information in this article came from www.mastergardeneronline.com Summer 2007 Page 21 – 23


Stinson, J. M., Brinen, G. H., McConnell, D. B., & Black, R. J. (1990). Evaluation of Landscape mulches. : Proceedings of the Florida State Horticultural Society 1990 Vol.103 pp.372-377 ref.7, 372-377 ref 7.