[USCC] juglone

[Greg Evanylo]

Experts are split on this issue. Some say that you can detoxify the 
juglone if you compost long enough (e.g., > 6 months). Haug even 
provides energy values of black walnut for use as chips in biosolids 
composting. See some of the comments below.

The West Virginia University site says: The largest concentrations of 
juglone and hydrojuglone (converted to juglone by sensitive plants) 
occur in the walnut's buds, nut hulls, and roots. However, leaves and 
stems do contain a smaller quantity. Juglone is only poorly soluble 
in water and thus does not move very far in the soil. Leaves, bark, 
or wood chips of black walnut should not be used to mulch landscape 
or garden plants. Even after a period of composting, such refuse may 
release small amounts of juglone. 
http://www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm

The Purdue website also says that composting may not completely break 
down juglone. http://www.hort.purdue.edu/ext/HO-193.pdf

 From an Ohio State University Extension Fact Sheet: Walnut leaves 
can be composted because the toxin breaks down when exposed to air, 
water and bacteria. The toxic effect can be degraded in two to four 
weeks. In soil, breakdown may take up to two months. Black walnut 
leaves may be composted separately, and the finished compost tested 
for toxicity by planting tomato seedlings in it. Sawdust mulch, fresh 
sawdust or chips from street tree prunings from black walnut are not 
suggested for plants sensitive to juglone, such as blueberry or other 
plants that are sensitive to juglone. However, composting of bark for 
a minimum of six months provides a safe mulch even for plants 
sensitive to juglone. (This pub also lists plant species and their 
sensitivity/tolerance.) http://ohioline.osu.edu/hyg-fact/1000/1148.html

Bonnie Appleton et al. says one can detoxify black walnut leaves in a 
compost pile. http://www.ext.vt.edu/pubs/nursery/430-021/430-021.pdf

My recommendation would be:
1. Don't use significant quantities of black walnut (and a number of 
other such trees that produce allelopathic compounds (e.g., red 
cedar) if you plan on applying finished compost to sensitive specieis
2. If you have incorporated walnut chips/sawdust into the compost 
pile, continue to process for longer than usual
3. Use the finished product only on tolerant species

Greg

At 10:04 PM 3/25/2009, you wrote:
>Hi - questions on juglone.
>I have some black walnut wood shavings. Suitability of this material 
>as a carbon source?
>Cheers, Mike in Toronto
>
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Greg Evanylo
Professor and Extension Specialist
Crop and Soil Environmental Sciences (0403)
426 Smyth Hall, Virginia Tech
Blacksburg, VA 24061
Ph: 540-231-9739
Fax: 540-231-3075
Cell: 540-257-4647
gevanylo at vt.edu
http://www.cses.vt.edu/people/profiles/evanylo_profile.html