Wood chips are tiny pieces of wood, usually made out of whole trees, branches, and limbs.
While they can be used to make paper, textiles, and wood products like chipboard (and more recently, as fuel), they’re also an excellent fertilizer for gardens. They are renewable and easy to use as a mulch.
Not only are wood chips economical – you can easily create your own or obtain them for free from local recycling centers and arborists – but they also help keep unnecessary matter out of the landfills.
You’ll contribute less to fuel wastage and since they break down so slowly, you won’t need to replace them often in your garden.
Wood chips are usually composed of material of various sizes, so they’re more resistant to becoming compacted than other materials, like bark or sawdust.
Plus, this diversity supports a wide range of soil microorganisms, making for a healthier plant environment and more resistance to environmental stress.
Arborist Chip Mulch
This material is a source of chips that come from the byproduct of your local tree service or work done by arborists. It can include any part of a tree removed by an arborist or service: berries, branches, leaves, blooms, and even roots.
This is natural, organic matter that has been run through a wood chipper. Usually, it is the remnants of tree service that have been broken down into arborist wood chips. Sometimes this is old trees, and sometimes it’s fresh wood.
It’s also common to find arborist chip mulch available in areas where orchards are prevalent.
Bagged Wood Chip
You’ll typically find this at your local hardware store or plant nursery. It is mulched tree matter in 2 to 3-inch chunks. It could be natural and organic, tree matter directly from a lumberyard or a tree service, and it may be wood that has been chipped on a mass scale.
Most of the time bagged wood chips are from trees that have been used in industry, not from fresh and recently harvested wood. But getting these means you’re also getting plastic bags that you’ll be sending to the nearest landfill.
Modified Wood Chip
These could be bagged wood chips that have been treated to reduce their flammability. They may be treated with pesticides and herbicides which prevent weeds and insects from taking over your garden.
This material is often used in situations where a homeowners association has designated a preferred color of mulch. Sometimes they’re reflective or dyed a particular color. They may contain chemicals as well as organic matter.
Think of any wood chip that has been introduced to some form of additive to prevent disease, weeds, fire, or to colorize it. As before, it’s bagged, which means more plastic for the landfill.
Bark Mulch
Bark mulch is shredded tree bark that comes from varying sources. Most are directly from trees and people who work with trees. Other sources are sawmills and furniture manufacturers, just to name a couple. It’s an absorptive mulch that comes in flakes. It can often be full of slivers, and it can easily become matted together, but the fine particulate looks great in a garden.
Shredded Wood Mulch
This is the stuff you’ll see in neighborhood gardens. Shredded wood mulch may be dyed, but is usually finely shredded material such as pine shavings. Generally speaking, this is a finer size mulch of about 1” or smaller in size, making it quite visually appealing.
It’s generally a byproduct of lumber and paper manufacturing, and it’s spread to provide an aesthetic uniformity by retaining moisture and blocking out weeds. However, it comes with a drawback; it can sometimes be fine enough to become matted together and can slow drainage slightly.
What to Avoid
In most cases you can put the branch trimmings and deadfall from your property into the chipper. The majority of native trees are acceptable for wood chips, but there are some species and forms of wood that should be avoided.
Naturally occurring toxins are present in a few trees used as landscape decoration. These toxins can be harmful to you or to your plants. In some cases, toxins can be absorbed through the chips and into your plants.
The EPA suggests avoiding black walnut for any composting or wood chipping work. Some additional species to avoid are:
- Oleander
- Sassafras
- Yew
- Black Walnut
- Eucalyptus
- Poison Oak
Pros And Cons Of Wood Chip Mulch
Let’s discuss the benefits and pitfalls associated with each as a source of mulch or compost. That way you have considered them before you are already using wood chip mulch at home.
Benefits
In general, wood chip mulch, when applied correctly, can be an excellent source of nutrients for your soil or compost pile. Wood chips also retain water in the soil, reduce weeds, and remedy topsoil erosion.
Ask any regenerative agriculture nut, and they’ll tell you wood chips simulate the same process that occurs on the forest floor, one of the richest environments around.
Wood chip mulch is a great way to prevent mud development in your garden because of its water retention properties. It looks great in any landscape, especially if you’ve managed to color coordinate. Some wood chips, like arborist wood chips, can even be free.
Adding a layer of wood chips to the ground to cover the soil surface, to reduce grass growth around trees, or to fill a muddy patch is a great way to carry out mulching in a natural way. Some modified wood chips keep pests out of the garden, allowing regular healthy growth to occur. Shrubs surrounded by a layer of red material can offset grass rather nicely.
Another great use for wood chip mulch is as a temperature regulator. Throughout the winter months, mulched plants often have warmer root systems, enabling them to withstand colder conditions much more readily. A thick layer of wood chip applied in the fall can be the factor that keeps your plants from severe weather damage.
Some types of mulch, such as aromatic cedar, can reduce pest populations. The aromatic nature of the wood acts as an effective deterrent.
If you’ve ever spread wood mulch you know it’s a great way to add a dash of pizazz to your landscape that will last for more than just one season. And when it does break down, you’re building rich soil!
Drawbacks
There are a few issues to consider, however, when it comes to working with wood mulch.
For one thing, many are concerned that these chips can pull nitrogen out of the soil. They do reduce the nitrogen level in the top inch or so of the soil, but further down the fertility of the soil is unaffected. This makes them a great choice for weed reduction, but not great if you’re starting seeds! Don’t mix mulch into the soil, as that puts the decomposing material closer to your plant roots.
They can choke plants and trees if they’re not used properly. The term “volcano mulch” is common in referring to trees with a mound of mulch right against the trunk. This style of mulching trees and other plants is dangerous, as it can cause damage to the trunk or plant’s base.
Compost and wood mulch together can make water retention too high for some plants and trees. They could experience root rot as a result. Usually, this is less of a problem for larger chip sizes, but it can be an issue in fine stuff like shredded barks or shredded wood chips.
Although colorful wood chips will last for more than one season, they do fade over time. For those looking for uniform color, you will regularly need to top-dress to maintain the right shade.
Where To Use Wood Chips
Yes, wood mulch on the soil surface is a great way to mimic the soil of a rich forest floor. But there are right and wrong times to spread mulch. There are specific ways to layer them with compost, and correct ways to spread mulch around plants, trees, and shrubs.
Proper Timing
Mulch is not something you want to plant directly into. You should wait to even spread it on soil that you have recently planted seeds in. Wait for your plants to grow before adding mulch as a ground cover. This keeps developing roots open to nutrient absorption. This goes for transplants to… make sure roots are significantly developed before you add fresh mulch to the soil.
Proper Spacing
One very important thing to remember for adding mulch to soil in a vegetable bed or a place where trees, plants, and shrubs live is to avoid mulching directly to the stem or trunk. Leave some space between the plant, tree, or shrub and the mulch. This not only allows tree, plant, and shrub respiration, but it also gives them a little moat where moisture can collect and be used slowly and gradually.
The reason mulch gets the reputation of nitrogen-stealing has to do with improper applications like volcano mulching. Even if the mulch is organic and from a tree service where a healthy tree is chipped, too close or too much mulch is a recipe for disaster. Improper mulching can kill a plant.
Mulches should not be applied to the soil where plants are growing in a layer more than 4 inches deep. 2 inches is the minimum depth. Any less than 2 inches and weed suppression is not possible. If you spread mulch on the ground for suppressing weed growth, remember this!
In areas where you’re trying to prevent plant growth, a layer of 6-inch deep mulch is perfect. This prevents weed development and reduces the frequency of replenishing the mulch layer. 6 inches is great for pathways, for example.
Proper Sourcing
Make sure you’ve found a good source for mulch. If you want to grow vegetables, green mulch, or some hardwoods like walnuts may not be the best option for your situation.
Most vegetable gardeners prefer softwoods like pine that break down easily so they don’t have to worry about improper plant growth.
Hardwood applied in the wrong situation can kill a plant. Some, like black walnut, are allelopathic and can actually reduce plant growth where they’re placed. While black walnut does decompose and the allelopathic conditions subside, it can take a while. Consider the tree species of mulch when you are planning.
If your mulch is purely an aesthetic choice, you may not need to worry too much about the source. But to make your organic gardening easier, you’ll want to make sure that the supplier you source from doesn’t include material that contains fungal pathogens or disease.
It’s terrible to have to come back from a free wood chip (which is great!) that is full of diseases and pulls nitrogen away from vegetables (bummer). Personally, it’s taken me years to come back from that in one of my vegetable beds.
Good sources for mulch are often local tree services or sites like ChipDrop. However, you can also get it from your local garden center, either bagged or in bulk. Typically, material from a garden center has been steam-sterilized, giving it an extra measure of protection from pest or disease transmission.
Building Soil
Maybe you prefer to use a mulch to build soil. In this case, it can contain green matter, and it can be hard wood. You can lay it in between beds to break down over time, or you can use it as a pathway. Green wood is great for this purpose as it’s still fresh from chipping, and may actually include some green leaves to provide nitrogen. This will reduce nitrogen loss as it breaks down, too!
Wrap-Up
Wood chips in a garden are an essential and often underrated tool. They are a natural, effective form of weed control. They provide insulation to valuable plants through winter. They create quality soil amendments over time.
By taking the time to clear up your deadfall and save up those pruned branches, you can provide for yourself and your plants on the homestead.
The next time you’re about to head off to the landfill with that load of brush, or set fire to that slash pile, take a moment to reconsider the hidden benefits of those little wooden chunks. Give them the opportunity to bring new life into your garden.
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