Sawdust For Garden Use – Tips For Using Sawdust As A Garden Mulch

By: Liz Baessler

Mulching with sawdust is a common practice. Sawdust is acidic, making it a good mulch choice for acid-loving plants such as rhododendrons and blueberries. Using sawdust for mulch can be an easy and economical choice, as long as you take a couple simple precautions. Keep reading for more information on mulching with sawdust.

How Can You Use Sawdust as Mulch?

Some people who put sawdust down as mulch in their garden shave noticed a decline in their plants’ health, leading them to believe that sawdust is toxic to plants. This is not the case. Sawdust is woody material that needs nitrogen to decompose. This means that as it biodegrades, the process may draw nitrogen out of the soil and away from your plants’ roots, making them weaker. This is much more of a problem if you incorporate the sawdust directly into the soil than if you use it as a mulch, but even with mulch, it’s still worthwhile to take precautions.

Precautions When Using Sawdust for Garden Use

The best way to prevent nitrogen loss when you use sawdust as a garden mulch is simply to add extra nitrogen with its application. Before laying the sawdust down, mix 1 pound (453.5 gr.) of actual nitrogen with every 50 pounds (22.5 kg) of dry sawdust. (This amount should cover a 10 x 10 foot (3×3 m.) area in your garden.) One pound (453.5 gr.) of actual nitrogen is the same thing as 3 pounds (1+kg) of ammonium nitrate or 5 pounds of ammonium sulfate (2+ kg.).

Lay the sawdust out to a depth of 1 to 1 ½ inches (1.5-3.5 cm.), taking care not to pile it up around the trunks of trees and shrubs, as this can encourage rot.

Sawdust can decompose at a fast rate and compact upon itself, so if you use sawdust as a garden mulch, you will probably have to replenish it and refluff it every year.

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When I was child, in northern Minnesota we use to play around huge sawdust piles from my Granddad's sawmill. They were already decades old, always moist, yet never decayed. There wasn't any nitrogen available for the composting process. Nothing grew in those sawdust piles, not even weeds.

So using sawdust, even with added nitrogen fertilizer, will be a bumpy ride, because estimating how much nitrogen you need is a crap shoot. In the end, you'll be fine but in between, I don't think so. Best to use the sawdust in a compost pile with ample green material as a nitrogen source.

DH brings sawdust home from work occasionally, but I've never used it as a first or only mulch material. It's spread/slung around beds where decomposition of a myriad of organic matter is already happening on the surface.

If you're able to add grass from mower bag, equal amount of grass or more, I would be confident about it going well. You would want to mow before grass (or other lawn plants) has seed heads. Add more to the surface if it disappears while the sawdust still looks fresh (light in color.) Another option for mixing with the sawdust would be moist produce scraps. Pureé first if you don't want to recognize the bits (which would also greatly speed the decomposition process, and aid in mixing with sawdust.)

If you choose to use the plain sawdust with nothing added, adding a few successive additions of thinner layers might be your best bet, vs. adding everything you have in one thicker layer. More than an inch or so of any single kind of OM at a single time can form into an at least temporarily unproductive mat, that can sometimes shed water instead of absorb it, until the decomposition process gets going well.

I try to maintain a cover of constantly decomposing stuff, from compost to leaves, to grass clippings, whatever presents itself that's OK to look at in a given spot (or sometimes slightly buried if not.) Mulch doesn't have to come from a bag at all.

If the sawdust is only laid ON TOP OF the soil, as a top-dressed mulch, I think that the only place the N deficit can occur is in the top few millimeters of soil - the interface between N-starved sawdust and C-hungry soil. I don't think that microbes can reach out thousands of times farther than their own size to steal N from soil an inch away.

What would you say, Rick R? Is there any N deficit with top-dressing mulches, a little, a lot, or what? I assume we agree that sawdust mixed with soil causes more N deficit (like, a huge amount) than it does if layered on top.

I guess someone would have to do a study to be sure that fungi with long mycelia or hyphae can't digest cellulose at one end of the hyphae, and steal N with the other end, then transport energy compounds down and N up. My belief is that acti8ve internal transport like that is very "expensive" for a fungus to perform, so not very much of it happens.

But I've read many times that wood CHIPS cause N deficit only if mixed INTO soil (and seen it happen myself). A top-dressing of lots of wood CHIPS doesn't cause N deficit. Or so I've read in multiple places.

If a top-dressing of saw DUST were to decompose very fast (for example, if dusted with hydrated lime or maybe if dusted with some N source), organic compounds might leach downwards with rain. If enough of those leached into soil that was already N-starved, it might make enough difference to be detectable.

My general approach is to top-dress with wood CHIPS, not sawdust, so that air and rainwater can perk downwards unobstructed. Also, I can easily rake away a mulch of wood CHIPS when I need to. And few weeds will root in fast-draining wood CHIPS.

But any weed would love to root in sawdust, IF it can reach any N with its roots before it starves.

P.S. It might help avoid top-dress-N-deficit if you add any N fertilizer into the soil, and mix it in, BEFORE adding sawdust on top . If you add N on top of a top-dressing, the top-dressing is likely to catch and hold lots of the N, and accelerate the growth of anything breaking down the sawdust.

If soil microorganisms weren't so darn efficient compared to plant roots in gobbling up nutrients, the admittedly small physical reach of nitrogen sucking microorganisms would have little effect, long or short term. But because of the "thousand" times effect (I can't say if it's really a thousand), natural sources of adding nitrogen to the soil(that occurs with other mulches) is essentially void, resulting in an increasing nitrogen deficiency as plants struggle to remove the remaining soluble nitrates. Remember too, that a portion of these nitrates move down the soil column with the drainage of excess moisture, and out of the reach of roots. The soil becomes increasingly nitrogen deficient, though not in the way you might expect.

As for your other tangential statements(which I generally agree with), If you could explain the relevance to the subject at hand, I'd be happy to engage. Or, perhaps they were just comments.
---- But any weed would love to root in sawdust, IF it can reach any N with its roots before it starves.

---- But I've read many times that wood CHIPS cause N deficit only if mixed INTO soil (and seen it happen myself). A top-dressing of lots of wood CHIPS doesn't cause N deficit. Or so I've read in multiple places.

---- I guess someone would have to do a study to be sure that fungi with long mycelia or hyphae can't digest cellulose at one end of the hyphae, and steal N with the other end, then transport energy compounds down and N up. My belief is that active internal transport like that is very "expensive" for a fungus to perform, so not very much of it happens.
I'm not aware of any internal "pumps" that require direct energy input to work. The mechanism(s) are there or not, and work as needed on their own. Indeed hyphae do transport nitrogen (and other compounds) regularly, but for your stated purpose, I have no idea.

10 tried and tested mulches

Which mulch is your best ally in the war against weeds?

Words: Jenny Somervell

I’ve tried them all, and despite their virtues, often extolled enthusiastically in garden books, they all have their advantages and disadvantages, and they mention nothing about what to do if you live with an infamous nor’wester like the one we have here in Canterbury.


Pea straw was recommended to us very early on and we still use it. It breaks down relatively quickly and is really a one-season mulch. However, it has its problems. The birds love it so the well-kept, tidy look I strive for with raised beds and brick paths is completely wrecked by birds spreading pea straw everywhere. Unless you like the wilderness look, be prepared to be annoyed. Also, unless you know the source, the weed seed and chemical content is unknown. I am pretty sure we introduced nettles and a good crop of dock which was hiding in our pea straw one year, and wild peas of course!


In small doses lawn clippings can work quite well. They are easily spread, even around small plants, but a little and often is better than thick layers. Thick layers tend to compact and rot, becoming slimy and smelly and often resulting in a build-up of trapped heat which can damage plants. If, like us, your lawn tends to the wild side with flowering clover and dandelions, avoid mulching when these are in flower or you risk seeding a new crop of weeds.


Best used as a base layer with a heavier mulch on top. Newspaper or cardboard layers can work well when laid thickly, and pre-soaking will increase weight and help to keep the mulch down in windy climates. Overlap the wads of newspaper so that weeds don’t come up between them. Avoid trying to lay newspaper and cardboard in windy weather.
To plant in it, you have to cut through the layers alternatively mulching around planted plants can be fiddly.

Sawdust has a very high carbon-to-nitrogen ratio (500:1) and can temporarily deplete soil of nitrogen. As the bacteria and fungi that break down sawdust multiply, they remove nitrogen from surrounding soil for their growth. Offset with a nitrogen-rich fertiliser, or better still, mix it with animal manures. Only use sawdust from untreated timber.

Untreated bark chips are popular in landscaping and work well if plants have hard woody stems. Depending on the size of the chips, they may take three or more years to break down but will eventually improve soil. Small chips are easier to spread especially around small plants. Like sawdust, decomposition can cause temporary nitrogen depletion.

Compost is partially decomposed organic waste and contains nutrients that are available to plants. Compost can be safely put in contact with young plants. Its dark colour absorbs heat and promotes warming of the soil. However, weeds love compost too – it is an ideal growing environment for seeds and, depending on how high the temperature rose in the decomposition process, may host weed seeds. I’ve had success covering the compost layer with weed-supressing mulches such as bark, sawdust, or pea straw.

If you can get it, seaweed makes a very fertile mulch for produce, containing every mineral needed in plant-available forms such as chelates and colloids.

Comfrey leaves laid as a layer on the soil around potatoes and tomatoes break down quickly if kept moist, releasing potassium and a host of useful nutrients. Against advice, I planted a patch of comfrey next to our compost heap as it is a good activator in compost. Of course, it has sneaked through the fence just as predicted.

Black polythene absorbs heat, prevents weed growth, and can be used to kill weeds. However, it also stops air circulating to the soil, can become a home for slugs, and becomes brittle with age.


My sister is a carpet gardener and she swears by it. “It takes ages to break down. You can scrounge it for next to nothing, and it forms a solid impenetrable mat.”


A couple of years ago we invested in a garden chipper/mulcher for dealing with our dead heads and prunings. We had developing hedges, 30-odd fruit trees, and a large working herb garden, all growing fast. We were advised not to buy a small machine as it wouldn’t handle decent-sized wood so the investment was quite high. My husband likes this machine so much that he leaves it on the patio, available for his instant use and constant amusement. I am sure it would be better off in the shed, but unlike some chipper-owners we know, at least ours get used!

What is Garden Soil?

Garden soil is the type of smooth, well-draining, nutrient-dense soil where vegetables (and other plants) will thrive. Garden soil is crafted over time by taking ordinary top soil and improving it.

Some gardeners carefully cultivate their garden soil for years on end by:

  • Sifting the soil to remove debris (like rocks, sticks, roots, and soil clumps)
  • Adding compost or aged manure (to add organic material and nutrients)
  • Adding supplements (such as fertilizers) to provide extra nutrition or adjusting pH (using lime or sulfur)
  • Rotating crops every year (to avoid nutrient deficiencies and plant diseases in the soil)

What is Garden Soil Used for?

Garden soil can be used to fill plant containers such as pots and grow bags. Well-cultivated garden soil provides an ideal environment for mature plants after they pass the germination and young seedling stage of development.

Use potting mix, rather than garden soil, when starting seeds indoors. This helps to prevent disease and other problems.

When germinating seeds indoors to grow seedlings, you should use sterile potting soil instead of garden soil. This reduces the chance that diseases, mold, or other problems will affect your plants.

Can You Use Garden Soil in Raised Beds?

Yes, you can use garden soil in your raised beds. As long as you improve the soil with compost or aged manure, you plants should grow well.

Soil in a raised bed will drain better than the soil in your garden, due to the extra elevation. As a result, you may want to use raised beds for gardening if your soil drains a little slowly.

You can use garden soil in a raised bed, and put a layer of mulch on top of it if you like.

DIY Mulch from Leaves

You can use fallen leaves from around your home for mulch for your garden.

  • First, you will need to collect all the leaves that are around the base of your trees or that you prune from your plants.
  • Next, rake the leaves into a mile on your lawn. Try to find a flat section to place them on. Then spread them out so they are about 2 inches thick. Use your lawnmower to shred the leaves. You may need to go over them a few times to shred them until they are about the size of a dime. This will help the leaves to decompose in your garden, releasing nutrients to the soil.
  • After the leaves are shredded, you can use them immediately to mulch your garden. If you have leftover leaves, store them in a large bag with holes to use as needed (just be aware that the nutrients will be lost over time, even sitting in a bag).

Pro Tip: Don’t use leaves from walnut or eucalyptus trees. These can prevent other plants for growing in.


Now you know how to mulch around onions, and what to use. You also know how to avoid some common mulching mistakes.

I hope you found this article helpful. If so, please share it with someone who can use the information.

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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Sawdust for Composting

First I would make sure the wood has not been chemically treated. Check a cross section of the wood for the distinctive ring of green color around the first half inch or so. If it has been chemically treated, it will contain chemicals like arsenic, chromium, and copper — not suitable for composting.

Make sure sawdust (and other carbon-rich "brown" materials) isn't more than about 80% of the material you are composting. That's just a basic guideline. You need some nitrogen-rich "green" material (living organics like leaves, fresh grass clippings, and other kitchen scraps) for decomposition.

Ideally, add the green materials and then spread sawdust on top of them.

Sawdust for Mulch

Sawdust is sometime recommended as an effective mulch for acid-loving plants (e.g. rhododendrons, begonias, impatiens, blueberries, etc), but for anything else, you will have to manage the acidifying effect as the sawdust decomposes. Wood chips and saw dust will rob soil of nitrogen as it decomposes, but since saw dust will decompose a lot faster, you may have to compensate the addition of nitrogen.

Keep in mind that saw dust can also compact severely over a single season, so you have to be sure to break it up periodically. Some people recommend a combination of straw and saw dust, but you have to watch for excessive water runoff nonetheless.

Watch the video: Super Effective Weed-Free Mulch From The Pet Store!

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