The name eucalyptus comes from the Greek, eu, meaning good (as in euphoria) and kaluptos, meaning cover. The prolific flowers and seedpods of these Australian trees are, indeed, well covered. And the oil produced by their leaves is good for many uses, but the greasy residue also has a dark side.
Eucalyptus oil has a great number of benefits and is used widely for its medicinal properties. At the same time, this prodigious oil, present in the fragrant leaves of the tree, is also known to be allelopathic. So while the oil may serve as an excellent natural remedy against stress, pain, anxiety and congestion, the eucalyptus leaves also contain chemicals which can impede the growth and survival of nearby plants and trees.
In California, eucalyptus trees grow like weeds. Literally. A century or two ago, someone had the bright idea to plant vast acreage around Morro Bay with eucalyptus trees. The enterprising venture proved a financial disaster, but hikers, bikers and nature-likers still enjoy the aromatic umbrage provided by the trees throughout much of Montaña de Oro State Park.
In addition to the good smells, cool shade and ideal lighting for family photos, the eucalyptus can offer a wide range of medicinal benefits.
Anyone who’s had eucalyptus growing in their yard knows that it can drop leaves all year long and pose a lethal threat to the rest of the garden. The leaves and seed pods get everywhere, almost impossible to remove, and leave behind a dirty residue. Not only is it dirty, but that oil is actually toxic to most other plants.
The botanical name for this is allelopathic. Certain chemicals present in the oil are seriously bad news for your ornamental horticulture and to native plants in particular. I’ve found a handful of non-native plants that can survive under the eucalyptus, but none will really thrive.
It seems like those that can produce their own oils stand the best chance of surviving under the canopy from down under. My lavender and rosemary plants actually did ok. But they were far from reaching their full potential, and always cluttered with euk leaves.
If you’re looking for weed abatement, however, then eucalyptus mulch can be among the most effective methods available. Eventually the allelopathic chemicals do break down, but under several inches of eucalyptus mulch, most weeds will struggle to germinate for a number of years.
Check out some of our other articles to learn more about itchy plants and bitter herbs, beneficial or otherwise.