Portland, Oregon, is a beautiful place to live, but those who love spending time enjoying their yards have a shorter season due to the cooler climate. This means you’ll want to be proactive and clear your yard and garden of common weeds.
Some weeds are considered invasive species in Portland, which means they impact wildlife and human health, negatively affect water quality, and pose a fire risk. It’s important to the City of Portland to do everything they can to help control these common weeds, but everyone can help by freeing their yards of these invasive and harmful plants and reporting certain weeds when necessary.
The best way to prevent an infestation of these plants is to avoid introducing an invasive species, which can be done by being educated about which common weeds are harmful and how to clear them out and keep them out. While there are many different invasive weeds, here are ten common weeds in Portland, Oregon, and how to clear your yard of them.
1. Yellow Archangel
This low-growing, aggressive plant thrives in shade and can quickly choke out native plants. It’s a dense perennial and has oval- to heart-shaped leaves, with greyish markings. The flowering stems grow one to two feet tall and yield small yellow flowers.
It’s best to hand-pull this weed in early spring when the soil is moist. Do this before it flowers in June to prevent the seeds from spreading. An herbicide can be used alongside manual control with extreme overgrowth. Be sure to wear proper protection, spray weeds before they go to seed, and remove any root fragments when pulling by hand.
2. Invasive Blackberry
Invasive blackberries have taken over many areas of Portland, often near streams and many natural areas. But they can also easily take over a yard. These invasive plants keep other native plants from growing, as they cover a large area and can block the sun.
It’s best to remove invasive blackberries when the soil is moist before seed formation. With a small infestation, manual removal is possible. With a larger infestation, you can cut away larger branches, and then use a lawnmower on flat, dry ground. Herbicides may be used for large, hard-to-control infestations where manual or mechanical removal are not possible.
3. Lesser Celandine
This invasive plant is a low-growing perennial that can quickly out-compete native and ornamental plants. Lesser celandine forms large, dense patches and spreads quickly by underground tubers and bulblets. The tubers are easily spread by animals or heavy rain and can grow in many different conditions.
Originally, this plant was purchased to be planted in the garden and can still be found as an ornamental plant. Identifying the lesser celandine early can help prevent spread, but with its short life cycle, there is only a brief window of time to control this invasive plant once it is established. Removing manually or with an herbicide (for largely affected areas) before or during early flowering in late winter is the best time to control the spread.
4. Old Man’s Beard
Also known as Clematis vitalba, old man’s beard is a vine so aggressive it can choke out native vegetation and even climb over and harm entire groves of mature trees. It blocks native plants from receiving sun and can weigh down trees to the point of falling.
Clematis is easiest to remove during fall and spring when the soil is moist and the ground is softer. This allows for the removal of roots. Early detection and removal are important, as this invasive plant can grow 20 to 50 feet a year, and once it’s established, it’s difficult to control.
Removing old man’s beard from a tree can potentially cause harm to the tree. Instead, cutting the vine and removing the roots completely will kill the weed, and the hanging vines will die on their own. Make a pile of the vines on two to three layers of cardboard to keep them away from the soil, and when composting them off-site, be sure no fragments get left behind. Confirm that roots are removed completely to keep the vines from forming new plants.
5. Garlic Mustard
This invasive plant is a groundcover that can grow not only in yards but in wetlands and forests as well. Once garlic mustard is established, it can produce a chemical that keeps native plants and trees from regenerating.
The best way to rid your yard of this invasive plant is to manually pull when the ground is moist and before it seeds. Garlic mustard doesn’t usually seed in its first year, so early detection is important.
When disposing of any plants with seeds, be careful to not spread seeds or leave plants out before disposing of them and risk seeds spreading.
Giant hogweed is an invasive plant that is a serious hazard to your health and should be removed by a licensed herbicide applicator only. Touching this plant can cause blisters, scarring, and blindness if the phototoxins released touch your eyes. If you think you have giant hogweed in your yard, Oregon law requires that you report it immediately for assistance.
7. English and Irish Ivy
These ivies thrive in shaded, moist environments and can easily take over areas with dense trees, potentially causing health problems for the trees and even topple them due to the heavy weight of an abundance of ivy.
Manual removal of ivy from trees is the first priority. Cut the vines about waist high and pull the roots when the soil is soft, taking caution to remove all roots to prevent regrowth. The vines on the tree will die after a few months, and it’s best to leave them alone to not cause damage to the tree.
8. American Pokeweed
American pokeweed is an invasive plant and is poisonous if ingested. Seeds are spread by birds, so if you have identified this weed in your yard, start by cutting off the flowers and dispose of them to prevent the spread and growth of more pokeweed.
Spring is the best time to dig up this weed, as it makes for easier detection and removal. This is a perennial plant, and though the flowers die back into the ground each year, the roots live through the winter.
9. Spurge Laurel
This shrub should not be handled without appropriate precautions, as the leaves, bark, and berries are poisonous if ingested and the sap can cause skin and respiratory irritation. Spurge laurel grows year-round but should be removed before the berries ripen in late winter or early spring.
Because of the toxicity of the plant, dispose of plants in a plastic bag and place them in the trash instead of home compost or compost at a facility.
10. Water Primrose
This invasive species blocks slow-moving waterways, as strands can grow to be 20 feet long. New infestations take place when break-offs float down to a new area. Controlling water primrose on your own is not suggested and in case of an infestation of water primrose on your property, submitting a report and getting assistance is recommended.
Mr. Tree is dedicated to working alongside Portland and its residents to control common weeds from taking over. For a full list of all nuisance plants, refer to this Portland plant list guide. We care about the health of our native plants and trees and encourage you to reach out, as we would love to assist you with any questions you may have.