[Arid_gardener] Composting Oleander and Eucalyptus

[Dick Gross]

Bcc: arid_gardener at CALS.arizona.edu 

There were recent questions and brief debate in this forum about the "carry over" of noxious compounds in materials subjected to composting. The quote below provided by Cathy Rymer will shed light on the subject. Thank you Cathy. 
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The Sept/Nov 1999 issue of the trade journal Southwest Horticulture had an article about compost made with oleander and eucalyptus. Dr. Jimmy Tipton and Libby Davison from the Dept. of Plant Science University of Arizona conducted these tests. The following are quotes from that article.

"There was no apparent phytotoxic effect of either eucalyptus or oleander compost. In fact, plant characteristics generally increased with increasing portion of either in the medium. Plants grown in a medium containing either compost were not significantly different from, or were superior to, plants grown in CM (commercially-available medium)" End quote.

These results suggest that whatever phytotoxic compounds that may be present in eucalyptus or oleander were destroyed by composting

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My observations (Further commentary invited)
One may presume the process should be complete to insure that potentially harmful compounds are rendered innocuous. 
There is also some debate about how to know when backyard compost is finished. Criteria I have seen frequently quoted, "When no fragment of the structure of the original plant is recognizable, the decomposition is presumed to be complete and ready to use." That does not certify that the finished product is safe.

I have seen pockets of untouched material in neglected backyard compost piles and bins where any toxicity would be intact. If you elect to use oleander, eucalyptus or any other questionable feed, you should, however, take steps to insure that the mass is frequently turned and maintained to complete decomposition.

Dick Gross, Master Gardener volunteer
U. OF A. Maricopa County Cooperative Extension.  

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