Invasive plants, by definition, are non-native species that grow aggressively. They are introduced from other regions and then adjust very favorably to their new environment. There is a significant distinction between non-native and invasive.  There are plenty of species of plants that adapt well to new regions that are similar to there native lands, both those species do not aggressively spread and overtake their new home.  So yes, these plants are not indigenous to the area in question, but they also spread rapidly. Indigenous plants that spread rapidly and overpower the competition tend to be referred to as simply “aggressive” or “ill-behaved”.

Why are Invasive Plants a Concern?

Invasive plants pose serious environmental threats. They compete directly with native species for moisture, sunlight, nutrients, and space. The introduction and spread of invasive species can degrade wildlife habitat, result in poor quality agriculture lands, degrade water quality, increase soil erosion, and decrease recreation opportunities. These impacts change nature’s balance on which all species depend.

Common Invasive Plants in Seattle

There is an nearly unlimited list of non-native and invasive plants, but here are several that I want to highlight. They are some common invasive plants found in Seattle, along with their scientific names and why they are a problem:

  1. Ivy (Hedera helix): Ivy is on the short list of my most hated invasive species. It is known to spread aggressively, forming dense ground covers but what bothers me the most is how it kills trees. It is so aggressive and parasitical that if left alone it destroys everything in its path. It is the biggest plant risk to our urban trees. The one redeeming quality is that it is holding up a lot of hillsides.
  2. Morning Glory (Ipomoea nil): Morning Glory is a vine with beautiful white flowers, but it is invasive and has a tendency to smother the other plants and trees that it grows on.
  3. Himalayan Blackberry (Rubus armeniacus): Blackberry bushes have to be my most loved and hated invasive species because I am a sucker for Blackberry cobbler. But they are very aggressive and quite difficult to eliminate their root structure is quite good at spreading and their seeds are spread everywhere from birds and animals enjoying the berries and spreading the seeds after consumption. The best way to take care of them is consistent and ongoing care.
  4. Holly (Ilex aquifolium): Holly is often thought of a lovely tree, but it is non-native and gross aggressively. It is also very persistent even when cut down to the stump. We often find it’s shoots coming through property lines and because it is so prickly it is difficult to maintain.
  5. Blue Bells (Mertensia paniculata): This may be the most controversial plant on the list because many people LOVE Blue Bells, but they are not native to the Seattle area. And they are very prolific, they spread via their bulbs but also their seeds. It doesn’t take long for a garden bed to be completely overrun by them. Interesting note, in the UK they are deeply cherished and NATIVE.
  6. Horse Tails (Equisetum arvense): Horse tails are extremely difficult to remove. They have a tendency to break as you weed them which makes getting the roots very difficult. We recommend very diligent and consitent weeding if your yard is overcome by them.
  7. Euphorbia (Euphorbia spp.): Euphorbia is another loved plant, but I wanted to put it on the list because it is non-native, invasive and caustic. I like to refer to it as a Dr. Seuss looking plant because of it’s striking nature, but we like to remove them whenever our customers allow. This is definitely a controversial opinion as many landscapers love to install them.
  8. Bamboo (Bambusoideae): Another one in a row that is contrary to many opinions. Bamboo is often described as one of the most sustainable plants on the plant and I understand the arguments. However, it is a non-native and invasive species to Seattle. We see countless situations where we are helping homeowners deal with their neighbors bamboo that was not properly managed. I want to highlight that Bamboo NEEDS to be managed, even with a bamboo barrier the bamboo will jump over the barrier and reestablish if not properly maintained. 
  9. Japanese Knotweed (Fallopia japonica): This plant is very invasive and although there is a beauty to the patches when they are in bloom, they are very aggresive and very difficult to remove. Often we see them growing through the cracks of concrete and have root bases under the foundation of a concrete landing.
  10. Mediterranean sage (Salvia aethiopis): This plant can form dense stands that displace native vegetation and reduce wildlife habitat.
  11. Milk Thistle (Silybum marianum): Milk thistle is good example of a Class A noxious weed in the state of Washington and Seattle. Class A is defined as “eradication required throughout Washington State including King County.” There are many others on the list. 

What Can You Do to Help?

Here are a few things that you can do to fight invasive plants and preserve the plant species native to your region:

  • Do not pick the flowers of noxious weeds and take them home.
  • Drive only on established roads and trails away from weed-infested areas.
  • Remove weed seeds from your clothes, shoes, and pets after visiting natural areas.
  • Replace invasive plants in your garden with non-invasive alternatives.
  • Volunteer at your local park or other wildlife areas to help remove invasive species.
  • Educate others about the threat of invasive species.

Remember, invasive plants are everyone’s problem. Spread the word, not the invasive plants! We try to help other Keep Their Corner of the Planet Healthy, you should too! If you are finding the weeds are too much to handle on your own, learn more about our Yard Care Services!

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