With summer nearing, Oregonians have surely been tending to their yards and gardens, planting, cutting, and digging up anything in their way. Some of us have returned this season to find new members to our garden community, or that last year’s nuisances have returned with a vengeance. A few of us even found our new additions ominously large and healthy.
Invasive plants truly put a hamper on achieving your dream yard or garden. They also have a huge impact on the environment by crowding out native plants, and on agriculture by degrading pasture. Often invasive plants arrive through national and international trade by accident, by expanding their ranges due to changes in habitat or climate, and through direct cultivation for agriculture and horticulture.
Because of this, the Emerald Chapter Native Plant Society of Oregon developed a list of gardening and landscaping plants that have become invasive in the Willamette Valley. Much of the Willamette Valley is susceptible to damage from invasive species because of the moist lowlands and floodplains spanning the region. The Willamette Valley is also the most densely populated region in Oregon, making it a prime location for cultivated invasives.
Before you hit the garden store, here is a thought-provoking list of 10 invasive plants originally cultivated for the garden. Don’t forget one of the best questions you can ask before taking a plant home is “How fast does this spread?”
Garlic Mustard – Alliaria petiolate
This stuff is nasty business. Introduced to the US as a garden herb with a two-year lifespan, garlic mustard is capable of producing hundreds of seeds per plant and crowding out most natives in the area. Its roots produce soil-degrading toxins and to top it off, the more you pull it, the more likely it is to return. Please report any sales of this plant to the FBI.
English Ivy – Hedera helix
This plant has been a traditional landscape favorite since English settlers arrived. Unfortunately, English ivy requires a lot of maintenance to keep under control and can climb anything from trees to powerlines. Outside of the garden, English ivy smothers native vegetation and trees. If you see this at the plant center, remember there are other options.
Kudzu – Pueraria montana
Kudzu is like Robert Patrick in Terminator 2—you put a gaping hole in it and it just closes right up. We are lucky in Oregon to have it mostly under control, but in the Southeast and in parts of Texas kudzu can spread up to 120,000 acres per year, smothering entire forests as it goes. It was brought to the US in the late 1800s for use as an ornamental vine and animal fodder. That worked out well.
Purple Loosestrife – Lythrum salicaria
Although purple loosestrife is an attractive flowering plant with a long bloom time, it doesn’t play nice with others. Brought to the US in the 1800s as a medical and ornamental plant, loosestrife took advantage of canal- and road-building to travel across the country. Loosestrife forms thick groupings along waterways where it can disrupt flow and crush native competition by releasing over a million seeds a year.
Reed Canarygrass – Phalaris arundinacea
Reed canarygrass hit the Northwest following logging and farming operations at the turn of the century. Initially used for soil stabilization, it later became popular as an ornamental grass. The problem is once this stuff hits the wetlands, it’s game over for pretty much everything else. Reed canarygrass can reach up to six feet tall and offers little benefit to wildlife.
Traveler’s-Joy – Clematis vitalba
The only thing joyful about this plant is traveling away from an infestation. Introduced in Oregon between 1950 and 1970 as an ornamental vine, traveler’s-joy can reach lengths of 100 feet, choke out forestry operations, and thrash your hedges in no time. If you cut one of these babies down, be ready because it will be back unless you herbicide the stump or dig the roots out completely.
Brazilian Waterweed – Egeria densa
If you have water on your property, then watch out for this attention hog. First noticed in New York in the late 1800s, this pond-polluter has reached across the planet through the aquarium and aquagarden trade. Waterweed will grow to the water’s surface where it begins to spread, forming a dense mat and preventing sunlight from reaching anything below. Fragments are capable of rooting and forming new colonies.
Giant Hogweed – Heracleum mantegazzianum
Giant hogweed is one of those plants that makes you hate nature. Arriving in the US in 1917 as, of all things, an ornamental landscape plant, giant hogweed can grow 6 to 18 feet tall, resprout when cut or not completely dug out, and burn the living crap out of your skin. Hogweed has a toxic sap that reacts with light to burn, blister, and scar your skin. Ornamental plant, right.
Pennyroyal – Mentha pulegium
This next one is a killer. An Irish native, pennyroyal is said to have arrived with English settlers as a medicinal plant. While not aggressively invasive, pennyroyal can dominate wetlands and ponds. Although consumed for health reasons, pennyroyal is toxic and can kill livestock and humans. In fact, the most recent death took place in California in 1994 when it was used to induce an abortion.
Himalayan and Evergreen Blackberry – Rubus armeniacus, Rubus laciniatus
The Himalayan blackberry is sort of a Frankenstein’s monster ordeal. In 1885 we thought it would be a good idea to cultivate it for its big berries, but the monstrosity escaped and now wreaks havoc all over the world. Naturally, birds work against us by eating the berries and spreading the seeds as they go. Able to grow over 30 feet tall and forming violently thorny thickets, this was certainly a failed experiment.
By Anthony Vitale