Sawdust can make a great mulch for your garden. It can help suppress weeds and insulate your soil. It’s often available for free. Sawdust can also be used to increase the acidity of your soil. This is great for acid-loving plants. Of course, there are some drawbacks to consider. Sawdust can temporarily deplete the nitrogen in your soil. It also soaks moisture out of your soil. This guide outlines the pros and cons of using sawdust as mulch for your garden. I’ll also explain how to apply sawdust and when to use it for best results.
Benefits of Sawdust Mulch
Sawdust is Cheap or Free
Sawdust is widely available. It’s easy to get sawdust for free. You could ask your local saw mill or even Home Depot. If you ask nicely, they will likely give you some for free. Just bring a bag with you and they’ll fill it up. Be aware that this sawdust could come from a number of different types of wood. It could also contain chemicals if the wood was treated.
You can also buy sawdust. It usually costs around $15 per yard. When you need a lot of sawdust, buying by the yard is economical. If you just need a small amount for a small garden, you can buy it by the bag online and have it shipped to your home.
If you can’t find sawdust for sale, you may have better luck finding wood shavings or wood chippings. These fine wood chips are commonly sold for bedding for small animals, like guinea pigs. Wood shavings can also work well for garden mulch. They perform similarly to sawdust.
Sawdust Can Lower the pH of Your Soil (Make it More Acidic)
If you have soil that is too alkaline, using sawdust mulch can be a great way to lower the pH or make it more acidic. Sawdust is also a good choice for acid-loving plants like blueberries, gardenias, and rhododendrons. Of course, this can also be a negative. You don’t want your soil to be too acidic. If you already have acidic soil, you’ll want to avoid sawdust.
Soil Temperature Regulation
Sawdust insulates the soil. It keeps the soil cooler during the summer by shading the soil. It also keeps the soil warmer during the winter by creating a barrier between the soil and the snow and ice. Sawdust also helps to minimize temperature swings between the day and night. This reduces stress on your plant’s roots. It can also help extend the growing season slightly. Sawdust is a great insulator.
It’s Easy to Apply
You can apply sawdust by hand. It’s lightweight and easy to transport. Try to lay it in a layer 1”-1 ½” deep on top of your soil. Sawdust doesn’t need to be as thick as other types of mulch. After applying the sawdust, you can smooth it out with a rake. You don’t need any special tools to apply it.
Weed Control
Sawdust acts as a weed barrier. It blocks weed seeds from reaching the soil. It also blocks the sunlight from the soil so existing weed seeds have a harder time germinating and growing. Some weeds will still grow but you won’t have to weed nearly as often as you would if the soil was bare.
It Helps Reduce Erosion
Sawdust blocks the impact of heavy rain on the soil surface. It also absorbs a lot of water. This can help prevent soil and nutrients from being washed away during heavy rains. Some of the sawdust can be washed away if the water is flowing but the soil will stay in place.
It’s Environmentally Friendly
Sawdust is a byproduct of the lumber industry. It is produced when trees are cut into boards and when boards are cut into smaller boards. Sawdust is a completely organic material. It is just made of wood. It degrades away over time. Sawdust doesn’t add anything bad to your soil, unless it comes from wood that has been treated.
It Lasts a Long Time
Sawdust mulch will last around a year before it needs to be replaced. That’s longer than mulches like straw or grass clippings, which need to be replaced multiple times per year. It’s not as long as wood chips or bark mulch, which will last 2-3 years.
It Looks Nice
Sawdust can be a nice-looking mulch. It is a nice woody material. I think it is more attractive than pine needles, shredded leaves, or grass clippings. It may not look as nice as wood chips or bark mulch.
Drawbacks of Sawdust Mulch
Sawdust Can Temporarily Deplete the Nitrogen in the Soil
As microorganisms break the sawdust down, they use nitrogen from the surrounding soil to fuel their activity. This temporarily reduces the nitrogen content in the area where the sawdust contacts the soil.
This nitrogen loss can weaken your plants and slow plant growth. Particularly if your plants are younger with shallow roots. Plants need nitrogen to grow. If you notice your plants aren’t growing as well after applying sawdust mulch, they may have a nitrogen deficiency.
Nitrogen depletion really only affects the surface of the soil, unless the sawdust gets tilled in. For this reason, it’s best to use sawdust only on established plants and larger plants.
It’s important to note that this nitrogen depletion is only temporary. As the mulch decomposes and the bacteria die off, the nitrogen is released back into the soil. This is an issue with all types of wood mulch, not just sawdust. It may be more noticeable with sawdust because it degrades faster.
You can avoid this issue by applying a nitrogen-rich fertilizer to your garden before applying the sawdust. Alternatively, you can mix nitrogen fertilizer with the sawdust. Another option is to apply a thick layer of nitrogen-rich compost then apply the sawdust on top. This will add extra nitrogen that you plants need.
Sawdust Can Soak Up Too Much Moisture
One of the main reasons people use mulch is to help retain soil moisture. This way, you don’t have to water as frequently and you don’t use as much water.
One major drawback of sawdust is that it actually soaks moisture out of the soil. Sawdust is commonly used for soaking up spills. It does a great job of absorbing liquids. After the sawdust soaks water out of the soil, the water evaporates away. Your plants can’t use the moisture in the sawdust. They need moisture in the soil, near their roots.
When you’re using sawdust as mulch, you may have to water more frequently and you may have to use more water. It’s a good idea to check that the soil is moist once in a while.
It Breaks Down Quickly
Sawdust doesn’t last as long as other types of wood mulch such as wood chips, shredded wood, or bark. This is because sawdust has more surface area for microorganisms to eat away on. They can break the smaller pieces down faster.
On average, sawdust will last around one year. To compare, wood chips or bark mulch will last at least 2-3 years. You’ll have to mulch more frequently if you use sawdust.
Sawdust Can Acidify the Soil
Sawdust is acidic. It can lower the pH of your soil. Usually, the soil acidification is pretty minor. It can be an issue if you already have acidic soil or if you grow plants that are sensitive to acidic soil.
Most plants like soil that is slightly acidic but not too much. The ideal soil for most plants has a pH of around 6-7.5.
It Doesn’t Add Many Nutrients to the Soil
One of the main reasons people use mulch is to make the soil more fertile by adding valuable nutrients such as nitrogen, potassium, and phosphorus. Sawdust robs your soil of nitrogen. It doesn’t contain many other nutrients. It just has a lot of carbon. It’s not bad for your soil. It just doesn’t add much to it, other than organic matter. It’s not a great soil amendment.
Compaction Can Be an Issue
Sawdust can compact. After it gets wet and starts to degrade, the sawdust can form into a kind of mat. This can block air and water from reaching the soil. It can smother your plants.
The best way to avoid this is to mix the sawdust with another type of material. This can help improve water and air penetration. The best material to mix with sawdust is compost. The compost will add valuable nutrients, such as nitrogen. It will also help to prevent compaction. You could also mix sawdust with other types of wood mulch. Coffee grounds can also work well.
Sawdust Can Contain Contaminants
You’ll want to be careful where you source your sawdust from. If the sawdust comes from treated wood, it could contain various chemicals. Sometimes wood is treated with preservatives. The sawdust could come from wood that was painted or varnished. You don’t want these chemicals contaminating your garden. This is particularly important if you’re trying to grow an organic garden.
Try to source your sawdust from a place where clean wood is being processed to avoid any chemical contamination. If you buy sawdust, it will usually be advertised that it is clean sawdust made from untreated wood.
Sawdust is not the Safest Mulch
Sawdust is an irritant. It can irritate your eyes, nose, and throat. Some people are allergic to it. You can suffer respiratory problems if you breathe it in. Sawdust can also be considered a carcinogen. In addition, sawdust can cause slivers.
For this reason, you’ll want to be careful while applying sawdust. Wear a mask and goggles so it doesn’t get in your nose and eyes. It’s also a good idea to wear gloves so you don’t get slivers. It’s not a good idea to apply sawdust mulch in areas where kids play.
After the sawdust settles and starts to degrade, it’s safe. Moisture will cause it to stick together so it won’t blow around too much.
It Can Wash Away
During heavy rains, sawdust can wash away if there is flowing water in your garden beds. You can prevent this by edging your beds to keep the mulch in place. Alternatively, you can use trenches to direct the flowing water away from your flower beds. For more ideas, check out my guide: How to Prevent Mulch From Washing Away.
It Can Attract Pests
Some insect pests could be attracted to sawdust. For example, termites could eat it. Ants could nest in it. If you have a serious pest problem, sawdust may not be the best option.
How to Apply Sawdust Mulch
- Prepare your garden- Remove any weeds, fallen leaves, or other debris. These make your garden look messy. They could also provide food for fungi.
- Add a layer of compost or manure (optional)- This can help avoid issues with nitrogen depletion. The compost or manure can add essential nutrients to your soil.
- Apply a layer of sawdust to the top of the soil around your plants- The layer of sawdust should be 1”-1.5” thick. You can mulch over your whole garden bed or just over the root system of your plants. Don’t let the sawdust touch the stem of your plants or the trunks of trees. This can cause rotting because sawdust holds water well. Leave a gap of at least a couple of inches.
- Water- After applying the sawdust, water thoroughly. After watering, stick your finger through the mulch to make sure the soil underneath is wet. If it’s not, your mulch may be blocking the water flow. It’s a good idea to check the moisture level of your soil periodically. Sawdust can retain too much moisture and cause the soil to dry out.
- Apply fresh mulch as needed- Sawdust degrades relatively quickly because the particles are so small. You’ll need to add a fresh layer around once per year.
When to Apply Sawdust Mulch
You can apply sawdust at any time of year. The best time to mulch depends on what you’re trying to accomplish. Are you mulching to insulate the soi or to keep the weeds down?
Most gardeners mulch in the early spring. The sawdust will help suppress weeds. Sawdust also makes excellent winter mulch. Apply it before the first frost to help insulate your plants during the frigid winter months.
If you have leftover sawdust after mulching, you can put it in your compost pile or compost bin. It’s a great carbon rich material.
My Experience
I use sawdust in my garden when I can get it for free. It’s not my favorite type of mulch but it works just fine. I am careful not to mix it into the soil. I make sure it stays on the top until it’s decomposed. This is to avoid nitrogen depletion. I also apply some compost under the sawdust to add some nutrients.
Sawdust can be an excellent mulch. It’s cheap or free. It helps keep the weeds down, insulate the soil, and reduce erosion. It can also help increase the acidity of the soil. There are some serious drawbacks to consider. Sawdust can deplete nitrogen in the soil. It’s also not very nutrient rich and it can soak up too much moisture. It’s also not the most long lasting mulch. Whether or not you decide to use sawdust as mulch, I hope this guide has helped in making your decision.
Do you use sawdust as mulch? Share your experience in the comments below!
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