Laidback Gardener Tip of the Day

Yes, You Can Compost Black Walnut Leaves

20151015ABlack walnut (Juglans nigra) and, to a lesser extent, other walnuts (Juglans spp.), as well as their close relatives, the hickories (Carya spp.), release a product called juglone that is allelopathic, that is to say toxic to most other plants. Thus, the walnut suffers little from competition, as few other plants can grow well at its base (here’s a list of plants that are resistant to juglone). Juglone is present in all parts of the walnut tree except the nut itself: leaves, branches, bark, wood, and especially its roots and nut husks.

The question is therefore: should the home gardener put “toxic” black walnut leaves in their compost bin? Ohio State University looked into the matter and the reply is yes: juglone decomposes within weeks in contact with air, water and bacteria. If the leaves are finely shredded, decomposition is even quicker. And once decomposed, walnut leaves apparently give a compost of excellent quality.

Walnut sawdust and wood chips as well as walnut husks, however, are slower to decompose: it is best to compost them for 6 months before using them in the garden to be sure the juglone has thoroughly decomposed.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

1 comment on “Yes, You Can Compost Black Walnut Leaves

  1. Pingback: Yes, You Can Compost Poisonous Leaves | Laidback Gardener

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