Mulching With Walnut Sawdust and Shavings

by Bill Tindall

Allelopathy is the secretion of a chemical by a plant that inhibits germination or growth of surrounding competitive plants. While walnut is the plant most associated with this trait, many other trees secrete allelochemicicals—for example, red oak, cherry, sycamore, sugar maple, and others. In the case of walnut the allelopathic chemical is juglone and it is secreted from all parts of the walnut tree.

Many plants are not affected by juglone, but tomato and blueberry are damaged by this chemical. While there is no doubt that tomato and blueberry could be killed or stunted if planted under a live walnut tree, it does not follow that walnut waste from woodworking presents a risk to these or other plants. Juglone is readily degraded by soil bacterial and may be destroyed by the lumber drying process.

Three observations suggest that the use of walnut waste from woodworking does not pose any special problem when used to mulch plants.

  1. I mulched half my pepper plants and half my tomato plants (four popular varieties) with about 6" of shavings from kiln dried walnut. During the growing season no difference in growth was observed between these plants and those mulched with other shavings.

  2. I added about one foot of fresh walnut sawdust from a sawmill to a garden spot and plowed it into the ground. The following year this spot was used for a garden and no adverse effects from the sawdust were observed.

  3. A friend prepared a plot for a commercial blueberry farm by adding about a foot of walnut sawdust to some land. Other than the need to add nitrogen removed by the decaying sawdust no adverse effects from the walnut were observed.

These observations suggest that kiln dried walnut waste, as well as partially composted sawmill waste, can be used as mulch or soil conditioner, even with sensitive plants.

Some of the information for this article came from Virginia Cooperative Extension Publication 430-021.

. . . Bill Tindall

© 2007 by Bill Tindall. All rights reserved.
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