Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
I saw a few small trees with colorful berries around a pond in a local park. I thought they were very pretty and wondered why they are not used in people’s yards. Turns out that they are an invasive plant called autumn olive.
What is Autumn Olive?
Autumn olive (Elaeagnus umbellata) is a flowering tree that is native to eastern Asia. Its range is from the Himalayas to Japan. It was introduced to North America in 1830 as an ornamental plant. By the 1940s it was being sold and planted as erosion control, wind breaks and as a source of food and habitat for wildlife. This practice was discontinued in the 1970s when it was realized that autumn olive was invasive, destroying natural habitats.
Autumn olives are easy to identify. They are a multi stemmed tree that grows up to 20 feet tall and 30 feet wide. The bark is gray. The branches have large thorns.
The leaves emerge early in the spring. They are silver in color maturing to green. The undersides of the leaves are covered with silver scales and are the most readily identifiable part of the plant.
The flowers are trumpet shaped and grow in bunches. They are fragrant and cream to yellow in color. Bloom time is May to early June.
The berries appear in August. They are red with silver scales that give them a rough texture. They are an important food source for birds and other wildlife.
Are the Berries Edible?
The berries are tart but edible. They are most often made into jams and jellies. If you are interested in cooking with the berries, be careful where you harvest them. Autumn olive can grow in heavily polluted soils, sometimes containing heavy metals. Those same pollutants, including heavy metals, are taken up by the roots and spread throughout the plant including the berries.
Why was Autumn Olive Used for Erosion Control?
Autumn olive was used for erosion control because it is able to live in poor soil. The roots are able to fix nitrogen in the soil. That mean that they are able to live in nitrogen poor soil because the roots contain nodules where bacteria live that are able to produce nitrogen that is necessary for plant growth. When you buy fertilizer the packaging will have 3 numbers on it. The first number is the most important. It indicates the amount of nitrogen that is contained in the fertilizer.
Autumn olive can live along stream banks, roadways, windbreaks and in polluted soils. It is not bothered by drought, disease, insects or deer. Deer eat it but usually use it for shelter instead.
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Why is Autumn Olive Considered Invasive?
Autumn olive is considered invasive for a few reasons. It leafs out early in the spring and then doesn’t lose its leaves until late autumn. That means that it is shading anything growing near it, shading out the nearby native plants.
The nitrogen fixing roots change the surrounding soil chemistry. Plants that need nitrogen poor soil are unable to survive in the vicinity of autumn olives.
The berries provide food for birds and animals, but they are not as nutritious as the berries that are borne on native plants.
Each berry contains one seed, but a mature tree can produce 30 lbs of fruit each year which yield 66,000 seeds. Those seeds are spread far and wide by the birds and animals that eat the berries and excrete the seeds.
How to Get Rid of Autumn Olive
How you get rid of autumn olive depends on how large the trees are.
Seedlings can be pulled up by hand. Wait until after a soaking rain so the soil is wet. When the soil is wet, you are able to get the entire root system when you pull the seedling from the ground. If you leave any part of the root in the soil, it will re-sprout into a new plant.
Full Grown Trees
Full grown trees are too difficult to pull out of the ground. It is best to cut them down. Then paint the stumps with an herbicide like Roundup. If you don’t use the herbicide, the stump will re-sprout into a new plant. You will need to re-apply the herbicide multiple times from spring until fall.
This tendency to re-sprout from trunks is why mowing seedlings doesn’t work unless you mow continuously throughout the growing season. If you just mow once, the seedlings and small trees will re-sprout. You need to mow over and over until the plants finally die.
Goats have been found to be effective in controlling autumn olive. They don’t mind the thorns on the branches. They can eat trees up to 5 feet in height. This is a slower way to control the trees. It takes a few years of goat grazing to completely eliminate the trees.
© 2020 Caren White