I have a couple questions about using sawdust in blueberry plantings . When fir sawdust is incorporated into the soil before planting does it lower the pH as it decomposes and does it also use up some of the Nitrogen in the soil? But when Doug Fir is used as a mulch on top of the ground does it lower the pH and use Nitrogen?
Clackamas County Oregon
Sawdust is primarily carbon and to decompose/compost, it must have nitrogen, so mixing it in the soil will definitely 'rob' nitorogen from the soil. If you haven't already found this publication, https://catalog.extension.oregonstate.edu/sites/catalog.extension.oregonstate.edu/files/project/pdf/...
it helps explain how best to manage blueberries in your home garden. Before you start doing anything, it's important to do a soil test and then amend to make your blueberries vigorous and productive.
Sara, Thank you for you quick response. I have read the publication, but it does not answer my specific question about pH. " Does adding sawdust into the planting area lower the pH of the soil?" And does using the sawdust as a mulch on top of the soil lower the pH?"
the answer to both is yes. But you *really* need to know what your starting soil pH is. Just adding sawdust is going to cause other issues if you don't ensure there is adequate nitrogen so it can break down without affecting your plants. You need to ensure you have adequate 'macro nutrients' of N-P-K for your plants and for the decomposition of the sawdust.
Using sawdust as a mulch has it's own problems because it can form a mat, preventing water from reaching the soil. the soil/mulch interface will be 'robbed of nitrogen to help decompose the sawdust but it's a little different than mixing it into the soil.