While looking through reader comments in articles recently, I saw that someone had commented on Lorraine Flanigan’s article Blanket your garden with a cosy winter mulch. The question was whether or not you can use sawdust to cover your bulb beds. I wasn’t sure how to answer this question, so I consulted Anne Marie. Here is what she had to say:
The sawdust will add another layer of insulation in addition to the soil and protect the bulbs during winter. However it should be removed or amended in the spring. Sawdust is a high carbon source (almost 40%) and when it decomposes in the garden it can divert microorganisms from helping plants obtain valuable nitrogen fertilizer. It can easily cause a nitrogen deficiency when it is breaking down as a result. This can be compensated for by adding additional nitrogen from fertilizer (for the plants) while the sawdust decomposes. The estimated carbon:nitrogen (C:N) ratio for sawdust and wood chips is 500:1 while composted manures are usually in the 17-50:1 range. A C:N ratio of 30:1 is considered ideal. Sawdust can be used in the garden, but after it has been composted. Use it in a compost pile with lots of “greens” to provide the offsetting nitrogen source. The nitrogen sources can be lawn clippings, vegetable kitchen waste, garden refuse but not leaves which are another carbon source. Some gardeners just pile the sawdust in the back corner of their yard and let it sit for a year and then it should be safe to use. So, remove it before it robs too much more nitrogen from the soil, put it in a pile in an out of the way place and add a high nitrogen fertilizer throughout to help with the decomposition process.