Conifers Gardening Mulching

Can You Use Conifer Wood Chips as Mulch?

You can use almost any anything left over from woodworking
as a mulch, and that includes conifer shavings.

By Larry Hodgson

Question: My husband planes a lot of larch and that generates a large quantity of wood shavings.

Can we use these shavings as a mulch for our perennial beds? Or for our berry patch where we grow haskaps (honeyberries), raspberries and blackberries? And if so, can I use 100% larch mulch or should I mix it with some other material?

Manon Huard

Answer: Any type of wood chip* or shaving left over from woodworking can be used as a mulch, and that would indeed include larch shavings. You just have to take into account how the choice of product will affect the results.

*In this article, I’ll use “wood chips” as the general term for small pieces of wood, including shavings from planing wood, pieces of wood formed by running branches through a chipper spreader, logging residues, residue from stump grinding, etc.

Mulch: A layer of material applied to the surface of soil.

With conifer chip mulch, you can expect to enjoy most of the benefits common to mulch use. Those include:

  • Improving visual appeal;
  • Preventing weed seed germination.
  • Keeping the soil more evenly moist;
  • Reducing evaporation;
  • Cooling and stabilizing soil temperatures;
  • Reducing soil compaction;
  • Protecting against erosion;
  • Providing shelter for beneficial animals.

However, there is one major benefit of most other mulches, but that conifer chip mulches are weak on. That is ensuring good soil fertility.

Wood chips derived from conifers tend to be low in minerals . . . or rather, they release the available minerals in only small quantities and over many years. So, they don’t enrich the soil as quickly or efficiently as a “rich mulch” (straw, shredded leaves, ramial chipped wood, etc.) would.

So, if improving the fertility of the soil within a reasonable time is your goal, you need to do more. Such as mix in a product richer in minerals. That could be compost, manure, grass clippings, shredded leaves or others.

Mulch Color

Wood chips from an unknown source.
Conifer chip mulches will become increasingly brown over time. (Here, wood chip mulch of unknown origin.) Photo: pxhere.com

Don’t worry about the almost white coloring of freshly produced larch chips. Yes, they can be shockingly pale. But that’s only temporary. Fairly quickly, they will turn a beautiful and quite regular earth-tone brown much like any other mulch.

A Few Myths About Using Bark Chips as Mulch

Myth 1: Conifer Chip Mulch Will Acidify the Soil

Several websites accuse conifer chip mulches of acidifying the soil.

In fact, however, mulches, regardless of their composition, don’t seriously alter soil pH, even after long years of use. After all, they’re above and the soil you might be concerned about is below. It’s, biologically speaking, two different worlds. Therefore, potential soil acidification is just not a significant factor.

And, of course, are conifer wood chips really all that acidic anyway? Common knowledge says they are, but acidity and alkalinity change as products decompose. They can be very acidic at first, with a pH as low as 4! However conifer parts become more alkaline as they rot. By the time they’re fully decomposed and begin to integrate the soil, they’re no longer very acidic. Most end up with a pH of about 6.5 to 6.8. And while, yes, theoretically, that is just a tad acidic, most gardening specialists would agree that it is just about the ideal pH for gardening.

So, soil acidification is simply not an issue.

Myth 2: Conifer Chip Mulch Will Steal Nitrogen from The Soil

Garden where conifer shavings serve as mulch.
The use of mulch of conifer chips is not a likely cause of nitrogen deficiency. Photo: landscapemulch.com

The second myth is that conifer chips will steal nitrogen from plants. This belief comes from the understanding that wood chips need a lot of nitrogen for their decomposition. And will steal it from the soil around them. This phenomenon is sometimes called “nitrogen starvation.”

However, since mulch normally remains on the surface of the soil, there is only a very thin interface where there is even possible. And add to that the fact that conifer chip mulch decomposes over a very long period of time. The result is that there is almost no effect on the soil’s nitrogen level.

In addition, even when mixed with the soil, as sometimes happens with mulches, slow-to-decompose conifer chips have a greater tendency to attract microbes (especially bacteria) which assimilate atmospheric nitrogen. So, in fact, they end up enriching the soil in nitrogen. Well, to a certain degree. Certainly, they don’t starve it.

That’s not to say that adding a nitrogen-rich fertilizer, like blood meal, might not be helpful to soils mulched with larch chips. Almost any soil can benefit from more nitrogen; this element is at a low supply in most soils! But the soil under a mulch of conifer chips will not need more nitrogen than another.

So, let’s also put the fear of nitrogen starvation, at least in this case, in the huge basket of “horticultural myths.”

What About Fire Risk?

Just about any organic mulch could eventually catch fire. However, wood chips are very coarse and are actually less likely to catch fire than fine-textured organic mulches. That said, certain safety precautions are always wise, especially in hot, arid climates where the risk of fire is greatest.

For example:  

  • Leave a space 18 inches (45 cm) wide clear of any flammable mulch at the base of combustible building exteriors such as wood or vinyl siding;
  • Use non-flammable materials like stones, gravel or mineralized wood mulch as a barrier in the first 18 inches (45 cm) around the foundation of a building;
  • Where you’re allowed to water, keep the mulch slightly humid at all times.

Simple enough in most climates!

How Did You Plan to Use Your Chip Mulch?

Circle of bare earth around the trunk of a young tree. No mulch applied yet.
A mulch of conifer chips will work well to attractively cover the ground around a tree while improving its growing conditions. This planting is awaiting its mulch application! Photo: sergii.kl.ua, depositphotos

Basically, deciding whether a mulch of conifer chips is beneficial from a home gardener’s point of view or not mostly depends on the intended use. And that’s because of its durability.

Because the conifer chips persist for a long time. A long, long time! Often a decade or more. This is because of the various suberins, tannins, and other decay-resistant compounds they contain.

A long-lasting mulch is great when you mostly want to use for its decorative effect. On the other hand, conifer chips that accidentally work their way into the soil and remain there for years complicate the life of the gardener. The presence of irregular bits of wood mixed into the soil makes sowing difficult, impairs root penetration, causes the root vegetables to grow crooked or to fork, etc.

For those reasons, it’s better to use conifer chips mostly as an ornamental mulch, around trees, shrubs and large perennials, or even in paths, etc. In other words, apply it to spots where you don’t garden intensively, with the idea that you won’t need to move it for many years.

Wood chip mulch used in a pathway.

You can use a conifer chip mulch in a pathway. It wouldn’t matter if it worked its way into the soil there. Photo; Susan Surman, forums.gardenweb.com

But not in a vegetable garden or a flower bed where you do a lot of digging, sowing, transplanting, soil amending, etc. In other words, where you frequently cultivate the soil, wood chips are just not welcome. Those are spots for finer mulches that decompose quickly and, indeed, are pretty close to being soil even as you apply them. Like chopped leaves.

Your Specific Situations

In your question, you were concerned about using larch chip mulch in your perennial beds and berry patch.

If you grow robust, full-sized perennials (hostas, peonies, etc.), don’t move them around or divide them often, yes. That would be a wonderful spot for using larch chip mulch. However, you could make it even better by mixing compost, well-rotted manure, grass clippings or shredded leaves with the chips. Say, three parts mulch, one part richer organic material. That will result in a richer mulch that will give even better results. Or simply get into the habit of regularly applying a slow-release complete organic fertilizer over your mulch. (No need to mix it into the soil below. Just broadcast it over the surface of the mulch and as the rain and irrigation water percolates through, it will carry the minerals into the root zone.)

However, if you sow on the spot, if the perennials you grow are short-lived and you replace them frequently or if you let them reseed themselves, you would probably prefer a finer mulch such as shredded leaves, straw or buckwheat hulls. That would also be true if you’re growing perennials as groundcovers. They would have a hard time establishing themselves through a fairly heavy mulch.

As for your berry patch, a larch chip mulch would be an interesting and long-lasting mulch. But again, consider adding a moderate amount of rich organic matter or even fertilizing regularly.

8 comments on “Can You Use Conifer Wood Chips as Mulch?

  1. Geoff Baldwin

    Another excellent commentary regarding larch shavings and wood chips in general. One experience that I had with my raspberry patch was that I added many many 6-9 inches of wood chips to the garden paths around my raised beds, however the raspberry patch wasn’t raised as it was the first bed in the garden. The next year the patch suffered tremendously, I chalked it up to nitrogen starvation and probably amending the wood chips around that patch with some nitrogen woold have helped. The patch recovered after some tlc and a bunch of google searches. But this was an extreme case as I happened to receive a huge amount of red oak wood chips and they were just so beautiful and the raspberry patch was not raised. The garden paths prospered and added a slight spring to my step especially after a rain.

  2. Good to know. I used our allotments free wood chip to make paths but it is mainly conifer so was a bit reluctant to use it to multch the fruit trees but now I know.

  3. Yes, exactly! There are wood chips that work well in compost, and wood chips that work well to inhibit weed growth. Sawdust from the machine shop here decomposes much faster, so is not so good for inhibiting weeds, but even a full bin of sawdust is less than a small pile of chips from the landscape debris anyway. In the landscape industry, black walnut, camphor and the various eucalyptus work well for inhibiting weeds. Here, we get bay and a bit of redwood, and sometimes a minor bit of cypress. Actually though, we can use any sort of chips to inhibit weed growth if we pile it on deeply enough. Some just inhibits weeds for a bit longer than others.

  4. billone

    Excellent comprehensive summary.

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