10 Invasive Plants Found in Northwest Gardens

Invasive plants can be a significant problem in our gardens and natural ecosystems if they’re not managed on a yearly basis. They have the ability to out-compete native plants, disrupt ecosystems, and cause harm to our regional Northwest environment. It’s good to be aware of these, since some are even sold in the big-box store retail nurseries, while others are just plain nasty . . .

Here are 10 of the most commonly found ones with links to curated images for reference:

1. English Ivy (Hedera helix): This vine can smother and kill trees and shrubs by blocking sunlight.
2. Himalayan Blackberry (Rubus armeniacus): Known for its thorny canes, this plant forms impenetrable thickets that crowd out native vegetation & attract small animals.
3. Scotch Broom (Cytisus scoparius): A shrub with bright yellow flowers, it spreads rapidly and displaces native plants. The flower dust is very aggravating to people with asthma & hay fever allergies.
4. Japanese Knotweed (Fallopia japonica): This tall, bamboo-like plant can damage foundations and is very difficult to eradicate. Not as toxic as Giant Hogweed, luckily. (Ask for help with this one.)
5. Yellow Archangel (Lamiastrum galeobdolon): It forms dense ground cover and can displace native plants in wooded or forested areas.
6. English Holly (Ilex aquifolium): A popular ornamental plant, its berries are spread by birds, leading to its invasion of natural areas. It does, however make a serious hedge with the spiky leaves.
7. Purple Loosestrife (Lythrum salicaria): This tall perennial produces dense spikes of purple flowers and can dominate wetland habitats around creeks & ponds.
8. Tansy ragwort (Senecio jacobaea): Tansy ragwort is toxic and a threat to livestock and agriculture. All plant parts are toxic, with the highest amount of alkaloids in flowers & leaves.
9. Butterfly Bush (Buddleja davidii): While loved for its attractive flowers, it can spread rapidly and displace native plants in a prepared garden. Yes, butterflies like it, so move it to outlying spots.
10. Giant Hogweed (Heracleum mantegazzianum): NO TOUCHING – This plant can cause severe skin burns and is a public health concern. Luckily, it’s not common. BUT GET HELP FOR THIS ONE.

Identifying the Invaders

It’s important to be aware of these invasive plants and take steps to prevent their spread. I’ve had the best luck identifying these invaders while in gardens by using ‘Google Lens’ on my Android Phone. (I’m a big Google user anyway . . . )

How to identify a plant with the Google Lens phone app

• Open the Google Lens app.
• Tap “Search With Your Camera” and grant the app approval to use your camera.
• To take a photo of the plant you want Google Lens to identify, tap the shutter button in the bottom center of the screen.
• Google Lens will show you search results and similar images.
• The 1st response is usually the most likely . . .

The Next Steps To Be Sure . . .

If you spot an invader, look it up & verify it’s on Washington’s Noxious Weed List here.

And, even better, if you have Washington State Master Gardeners locally, you can bring an example of a leaf or flower with a small stem to them to really make sure. They often carry picture books for just this purpose at their information tables in Saturday Farmer’s Markets & elsewhere . . .

Native Plants are Good Replacements

Should you have any of these plants in your garden, consider removing them and replacing them with native alternatives. I’ve had good luck with this up-to-date plant list from the Washington Native Plant Society here. Many are for sale at independent nurseries all over the Northwest.