Help for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client Request: I have several eucalyptus trees on my property. They shed a lot of leaves. I'd like to use the leaves for mulch and possibly compost, but when I research these uses, I get confusing and/or contrary guidance. My request: Can I use eucalyptus leaves/cuttings as mulch and/or compost in the home garden?
Help Desk Response: We understand your frustration with the information you're finding on the use of eucalyptus leaves as mulch. In doing the research on your question, I too, found a lot of conflicting information. The Master Gardener Program is under the umbrella of the University of California so the information that follows is all based upon scientific research.
Eucalyptus Toxicity
While it is true that eucalyptus leaves do have some toxicity, the research shows that well composted eucalyptus leaves pose no problem when used as a mulch or when mixed at appropriate quantities into a growing medium. The research also concluded that fresh eucalyptus leaves were shown to be a good weed suppressant when applied to a depth of 4 inches (10cm).
Following are two articles by James Downer & Ben Faber on the subject of eucalyptus mulch and eucalyptus compost.
http://ceventura.ucanr.edu/newsletters/Volume_23_No129817.pdf
and
http://slosson.ucdavis.edu/newsletters/Downer_199429100.pdf
Composting
The University of California research concluded that, when handled properly, eucalyptus is safe for use in compost (i.e., incorporated into the growing medium). The toxicity of the eucalyptus are rendered harmless by the composting process, especially if you are working a hot compost pile. (See http://vric.ucdavis.edu/pdf/compost_rapidcompost.pdf)
When composting eucalyptus, the leaves are considered green plant material and will constitute the nitrogen part of the composting process. To effectively use eucalyptus clippings or leaves, you will want to mix them thoroughly with carbon-based materials such as newspaper, cardboard or other dry leaves or plant material.
The University researchers suggest, if you still have concerns, that you consider composting eucalyptus in a separate hot compost pile, keeping the pile well moistened and turning it often to keep the mix hot over a longer period of time.
Once the eucalyptus is well composted you can do a germination test to test for toxicity by using the compost as a medium to start 10-12 fast growing seeds such as radishes. If a majority of the seeds germinate, the eucalyptus toxicity can be considered neutralized by the composting process.
If you want to use fresh eucalyptus leaves in your landscape, the conclusion suggests to favor using them on the woody landscape plants in the home garden setting.
I hope this gives you the information you were looking for and sets your mind at ease.
Help Desk of the UC Master Gardener Program of Contra Costa County (BHD)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/).