Sawdust and wood chips are a big part of some gardening methods. Sawdust is a cheap soil amendment, but should only be used in very specific situations.
Sawdust should not be used as a fertilizer in the garden, it will decrease the nitrogen in the soil as it breaks down. Soil that has been mixed with sawdust or fine wood chips will often produce yellow plants with poor health.
Sawdust can be a helpful soil amendment for sandy or clay soil that has trouble holding moisture, but the gardener should be careful to fertilize heavily with a nitrogen fertilizer at a rate of one pound per 100 square feet.
Sawdust can be used as a mulch in some gardening situations, but it should be paired with a long-term nitrogen fertilizer plan.
Can You Use Sawdust as a Fertilizer?
Sawdust cannot be used as fertilizer, mixing sawdust with your soil will degrade your soil and steal nitrogen from your lawn or garden. Soil that has been mixed with raw (unaged) wood chips or sawdust must be fortified with nitrogen-rich amendments.
After mixing sawdust with your garden soil you may notice plants growing poorly or turning yellow. These are the main symptoms of nitrogen deficiency in plants.
The very popular Back to Eden style of gardening recommends using wood chips on top of the soil to keep the weeds down and hold moisture in the soil.
Sawdust and wood chips can keep the moisture in the soil, but they should never be tilled into the soil.
Back to Eden methods require large amounts of nitrogen-rich compost.
This gardener recorded her two-year experiment with wood chips in her garden. This video shows her soil test results after two years of using wood chips.
She has been successfully growing a large garden for her family for two decades, so she has seen how her more traditional methods have been successful and the results of switching to using wood chips.
Soil that has been mulched with or amended with wood products should be tested with a simple soil test kit from Amazon or with a soil testing company.
If you find that your soil is low in nitrogen, consider adding compost or quickly decomposing soil amendments like wheat flour or coffee grounds.
Can Sawdust Be Mixed with Soil?
Sawdust can be mixed with very clay or sandy soil to help the soil hold moisture, but it will rob much of the nitrogen from the soil. If you find that you need to add sawdust to improve the moisture of your soil, add nitrogen at the same time.
Even if your first crop in sawdust amended soil performs well, test the soil before the next season and a heavy layer of compost should be considered.
As sawdust breaks down it uses a lot of the nitrogen from the soil and robs it from the plants. There are many ways to increase the nitrogen in your soil without nitrogen fertilizers.
Commercially available fertilizers like ammonia sulfate are very high in nitrogen and can be added to the soil at the same time as the sawdust.
Allow your soil to sit for two or three weeks after these additions before planting. Water it regularly during that time to distribute the nitrogen fertilizer.
If you are adding sawdust consider adding these nitrogen rich items at the same time:
- Ammonia Sulfite
- Milorganite
- Composted Manure
- Green Mature Plants
- Coffee Grounds
- Bloodmeal
- Cornmeal
- Alfalfa Meal
- Fish Emulsion
- Corn Gluten
These fertilizers should be added at a rate of one pound per 100 square feet. You can find out how much nitrogen is in your fertilizer by looking at the NPK ratio.
The N stands for nitrogen and the percentage of nitrogen will be listed on the product. A 20% nitrogen fertilizer will require 5 pounds of fertilizer per 100 sq ft to get a pound of nitrogen.
When doing your garden planning be sure to consider planting nitrogen fixing plants like peas and beans to help the overall soil health long term.
These plants grab nitrogen from the air and put it in the soil. Do not add supplemental nitrogen to the areas where you will be growing these plants as it can make them susceptible to disease and make their fruits bitter.
How to Compost Sawdust
If you find yourself with a lot of sawdust and you are hoping to use it in your garden consider composing the sawdust.
Sawdust adds carbon to the compost, so it should be layered with nitrogen auditions like green leaves and garden waste. Sawdust is considered a “brown” for composting purposes.
Sawdust takes a very long time to compost on its own and requires regular watering and turning to fully compost down into dark rich soil.
Once sawdust is composted it will no longer rob your soil of nitrogen and can be used like any other compost.
If you choose to age or compost a large pile of sawdust or wood chips, be sure to water and turn the pile regularly and expect the process to take two to three years to see much change in the wood product.
Sawdust can retain its original properties and not rot if it does have enough oxygen to facilitate the decomposition process.
I have heard several gardeners say they plan on using aged chips the next time they mulch with wood chips, if that is your plan, start aging your pile now.
This gardener found a gold mine of composted sawdust around an abandoned lumber mill. The linked video shows the color variations you may see and gives an example of fully composted sawdust.
It was interesting to see how long the sawdust can remain preserved under layers of dirt.
Other Uses for Sawdust in the Garden
While sawdust cannot be used as fertilizer in your garden it can be helpful in some situations. There are benefits of using sawdust for its other properties.
Breaking Up the Soil
Sawdust can be used to improve the soil texture of very heavy clay soil by improving its ability to hold moisture.
You can mix in sawdust and nitrogen fertilizer to the soil, allow it to rest for two to three weeks then plant as usual. Monitor the soil health and compost regularly to replace the nitrogen being used by the sawdust.
Over Fertilized Soil
Plants that have been over fertilized or are nitrogen fixing can be helped by the application of sawdust.
Plants that have too much nitrogen can have a bitter taste and make the plants susceptible to disease.
You may also consider using sawdust in areas where you will be using green mulch or cover crop to create a healthy soil over time. Be sure to test your soil after the process of tilling in the cover crop to be sure no further amendment is needed.
Sawdust will decrease the nitrogen in the soil, so it can be used as a tool when addressing garden and soil issues.
Mulching
Sawdust can be used to mulch around plants to keep moisture in the soil.
Sawdust is cheap or free and can be a good choice for mulching if you have trouble keeping your soil moist.
Be careful not to till the sawdust into the soil after the season is over as it will deplete the soil of nitrogen.
This gardener made this mistake and saw dramatic results in the following season of his garden.
His video shows what can happen to your garden if you mix in wood chips or sawdust and do not amend the soil with nitrogen.
Suppress Weeds
Mulching with sawdust can suppress weed growth in your garden.
This is a big motivator for many gardeners using sawdust to mulch in their garden. This will dramatically decrease weed growth in your garden, but should be done carefully.
Like I mentioned above you need to be careful not to till the wood products into the soil. Even with surface mulching the nitrogen will be used up by the rotting wood.
Grow Mushrooms
Mushrooms grow in rotting wood and sawdust can be used as a growing medium for mushrooms.
Many home and hobby growers create sawdust blocks to grow mushrooms. These are often made in bags with a mix of sawdust and millet or rice bran. These create ideal nutrient availability for the mushrooms.
There are several recipes for creating the grow bags for mushrooms and they are very simple to create.
If you know the type of sawdust you have growing mushrooms may be a good way to make use of the sawdust.
Support Cover Crops
A comprehensive gardening plan should include a plan for improving the soil each season. Adding sawdust to soil where you intend to plant a nitrogen fixing cover crop can support improved soil structure.
The sawdust will improve the soil’s ability to retain moisture which will support the growth of the cover crop and when you till them together you should have a balanced soil composition as a result.
Nitrogen Fixing Cover Crop Options:
- Berseem Clover
- Red Clover
- Crimson Clover
- Cowpea
- Field Pea
- Sweet Clover
Is Sawdust Good For Your Lawn?
Sawdust should not be added to your lawn as they will rob the grass from nitrogen.
Mulching your lawn with sawdust can help the lawn retain moisture, but you will need to add nitrogen fertilizer to your lawn as the sawdust will use up much of the nitrogen in the soil causing the lawn to turn yellow.
Too much sawdust on your lawn can smother the grass and keep it from growing well to begin with.
Sawdust is not recommended as part of lawn care as it will require regular fertilizer application and will degrade the soil quality over time.
Can You Grow Vegetables in Sawdust?
It is possible to create a small container garden with sand and sawdust. These small gardens require fertilizer very regularly, even daily.
Sawdust is not an ideal growing medium as it is almost completely carbon with no nutrients that plants need to grow and thrive.
Sawdust or other non-soil growing mediums are often used in grow towers or under grow lamps in indoor gardening set ups.
If you are using an indoor gardening set up you can make your own non-soil medium with the correct ratios of sawdust and sand with the addition of fertilizer in the initial mix and regularly after.
Sawdust is slightly acidic, so PH amendments may be necessary to create a suitable non soil growing medium. Soil PH is easy to test with a simple soil probe test available online.
Non soil mixtures are more commonly made of peat and vermiculite.
Using Sawdust In the Garden
Sawdust is not good for crop yields in most soil conditions, but it can be useful as a mulch when the soils is amended with nitrogen.
If you choose to use sawdust in your soil, test it regularly and monitor the health of your plants.
Adding liquid or granular nitrogen fertilizer or compost animal manure can help quickly increase the nitrogen in your soil.
If your soil needs to be improved because of a sandy or clay texture make a multi season plan for incorporating sawdust to improve the texture of your soil.
Each season should include the heavy use of fertilizer and the addition of other organic material.
Consider cover cropping or green mulching areas where sawdust have been used. The nitrogen fixing properties of a cover crop like alfalfa combined with the moisture improving properties of the sawdust can produce fertile soil over a few growing seasons.
Sawdust is cheap and easy to come by in areas where timber work is common. It is possible that you can attain truck loads of sawdust at lumber mills in your area.
Ask plenty of questions about any sawdust you are using. Black walnut sawdust leeches a toxic chemical that will destroy you plants. Pressure treated wood contains chemicals that you may not want in your garden.
Sawdust from tree removal can be used in your garden as long as you are keeping a close eye on your soil composition.