Using Sawdust as Mulch
Sawdust or shavings can be used as a plan mulch if you take a few extra steps.
Some people who use sawdust as plant mulch notice a decrease in plant growth or health and assume that the sawdust is toxic to plants. Not so.
Sawdust is woody material that needs nitrogen to decompose. As the sawdust biodegrades, nitrogen is drawn from the soil and is not available to support plant growth, especially plant roots. 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 when applying it. Before laying the sawdust down, mix 1 pound of actual nitrogen with every 50 pounds of dry sawdust. This amount should cover a 10 x 10 foot (3×3 m.) area in your garden. One pound of actual nitrogen is the same thing as 3 pounds of ammonium nitrate or 5 pounds of ammonium sulfate. Lay the sawdust out to a depth of 1 to 1 ½ inches, 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 it every year.