Eucalyptus Leaves Used as a Mulch

Q. What’s your opinion about using eucalyptus leaves as mulch?

Eucalyptus microtheca growing in Las Vegas

A. There are reports that leaves from some plants will sometimes inhibit the growth of others. I think this is what you are referring to. This inhibition of growth was first thought to be due to competition for water and plant nutrients, but plant chemicals have been isolated from some fresh plants and found to affect the growth of others. How this works depends on the plant making it and their “allelopathy” is not consistent between different types of plants. All this makes it difficult to isolate and prove its existence. It is clear to me that plants “communicate” in ways we have not thought about but how this happens is not clear.

Read more about eucalyptus leaves as a mulch here

Eucalyptus leaves as a mulch here

The classic example of this is black walnut inhibition of growth (allelopathy) on plants growing under its canopy. Other examples of “allelopathy” exist such as in creosote bush, lavenders, salt cedar, bermudagrass, and others. It is not just a simple answer but varies between allelopathic plants and plant parts. Personally, I have never tried using eucalyptus leaves. I prefer to use wood chips as a mulch or a combination of plant parts from different plants.

Oleander as a composted mulch

One way around this is to compost, or “rot”, eucalyptus leaves. It seems that in most cases the plant or human “toxins” are decomposed as well rendering what’s left as nontoxic to both plants and animals. So, for this reason, I would not use uncomposted leaves of any kind without composting (rotting) them first unless I knew the leaves were not toxic to other plants in the first place.