Autumn Olive was brought here in 1830, from China, and Russian Olive came from Europe and Asia in the early 1900s. They have been planted extensively for erosion control, land reclamation, and even for landscaping. You can actually buy these plants at some nurseries. Don’t do it!
If untrimmed, both Autumn Olive and Russian Olive will grow into small deciduous trees. They are actually attractive with small oval leaves which flutter in the wind and reveal a silvery underside. In the spring they are covered with small, yellow tubular flowers which have a cloying sweet odor that will fill the air. From late summer through fall, Autumn Olive is loaded with clusters of pinkish-red berries (actually a drupe- like a small cherry). Russian Olive has narrower leaves, and the fruits are yellow and elongated instead of reddish. Their potential beauty is far outweighed by their faults.
From now on I’m going to simply lump them under the term Olive, but all my comments pertain to both species. They are not related to the olives of the Mediterranean.
Why is it such a bad plant? It is truly invasive, and will take over any open space in which it gets a foothold. Once established it’s nearly impossible to eliminate. It appears to me to have some allelopathic properties, which means that it can exude chemicals to inhibit the growth of other plants in the vicinity. I notice that nothing will grow near large established clumps of it.
The plants are nitrogen-fixing, although not true legumes, which means they can draw nitrogen from the air, rather than the soil. This allows the plant to grow quickly in old fields or other areas where the soil is poor. It will quickly out-compete any native plants in such locations.
Adult birds love it. Autumn Olive produces round red to pink-rusty colored berries which are enjoyed by many species. Russian Olive fruits are more yellow. There is some evidence that small mammals also eat the fruits. But these animals also spread the plant everywhere because of this seed dispersal.
You might wonder how it can be so bad if the birds love it. It’s one of those complex food web relationships. Insects do not particularly like it. So when the plants take over an area, the local insect population declines. But baby birds need protein. Parent birds bring insects and their larvae as food for nestlings, almost exclusively. With fewer insects in an area, the survival rate for nesting birds is reduced.
If it is trimmed in any way, multiple suckers will grow from just below the cut area, turning the plant into a weedy bush with dozens of stems. And this is another of the reasons it is so difficult to control. Cutting just makes it happy.
The only good thing I can say about this plant is that the fruits are edible. Autumn Olive berries have a tart-sweet taste that is best in fall, just before hard frosts begin. So if you live in a location where you are battling this plant, you can at least enjoy something about it.
The better plan would be to join any local efforts to eradicate Autumn and Russian Olive.