Issue: May 25, 2002

Stump grinder mulch ok to use

Question:

Recently we had a large mulberry tree cut down in our yard. The person who removed the stump suggested putting the mulch or shavings produced by grinding the stump into the garden and tilling it into the soil. Can you tell me if this is a good idea, or are there any drawbacks to adding the shavings to the garden soil? Thanks for your time. Travis R.

Answer:

Adding the chips (shavings) to the landscape can be a good thing. There are some facts to keep in mind. A mulch is a material placed over the surface of the soil for a number of beneficial reasons. As a mulch, the wood chips will stabilize soil temperatures (warmer in winter, cooler in summer), reduce evaporation and conserve soil moisture, reduce germination of some weed seeds, and make removal of weeds easier. Wood chip mulch can be attractive when used properly in the landscape. The chips may blow away if they are too light and wash away in the rain if on a slope. Mulch is one element of a xeriscape and a component of any good garden.

If you work the wood chips into the soil, they will be used as a soil amendment instead of a mulch. There are different considerations when using the wood chips in this manner. They can be beneficial by creating increased pore space. In a compacted soil, they allow necessary air and water to more easily penetrate a compacted soil. The wood chips will decompose releasing nutrients into the soil. The decomposition will occur more rapidly if the chips are worked into the soil, but it occurs even if the chips remain on the surface as a mulch.

The decomposition process adds some additional considerations into the gardening equation. In order to decompose, the wood chips will be food for beneficial composting fungi and bacteria. The fungi and bacteria need the food materials provided by the wood chips and nitrogen to accomplish the composting process. Wood chips are low in nitrogen, so the fungi and bacteria will take the nitrogen from the soil. Large chunks of wood will decompose slowly. Smaller wood particles with a larger surface area-to-volume ratio will decompose more rapidly. This will cause nitrogen deficiency problems in the soil. If you are using fine shavings or sawdust as mulch or as a soil amendment, you should add additional nitrogen in the form of chemical fertilizer or manure to the soil to provide the needed nitrogen.

Using the wood chips in the landscape is an excellent idea, but it must be done properly. Keep in mind the considerations stated above so that you will do it properly.

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For more gardening information, visit the NMSU Extension Horticulture page: desertblooms@nmsu.edu.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.