Invasive Plant Species in Sooke

Sooke is a place where nature’s wonders abound; however, invasive (not native) plants impact our local ecosystem. The page intends to shed light on some of these unwelcome guests that’s easy to understand.

Meet the Invaders: Let’s start by getting to know our not-so-friendly neighbours:

  1. Japanese Knotweed: This fast-growing plant is like the superhero of invaders, spreading quickly and taking over our green spaces.
  2. Himalayan Blackberry: With its thorny vines and tasty berries, it might seem harmless, but this plant can take over fields and forests in no time.
  3. English Ivy: Picture a plant that loves to climb – that’s English Ivy! It can cover trees and buildings, making it hard for other plants to get the sunshine they need.
  4. Scotch Broom: You’ll spot this one by its bright yellow flowers, but don’t be fooled – it’s a master of disguise, disguising hillsides and crowding out native plants.
  5. Giant Hogweed: Don’t let its name scare you too much, but this giant can cause big problems. Its sap can irritate your skin, and it loves to hog all the space along our streams and rivers.

Why Should We Care? These invasive plants might seem harmless, but they can cause big problems:

  1. Nature’s Balance: When invasive plants take over, they push out the native plants that animals rely on for food and shelter, upsetting the balance of our local ecosystems.
  2. Fun in the Sun: Have you ever tried to play in a park that’s covered in prickly blackberry bushes? It’s not much fun! Invasive plants can ruin our favourite outdoor spots and make them hard to enjoy.
  3. Staying Safe: Some of these invaders, like Giant Hogweed, can even hurt us! Their sap can cause skin irritation, so it’s best to keep our distance.
  4. Saving Money: Dealing with invasive plants costs a lot of money – money that could be better spent on fun things like building new playgrounds or planting more trees.

What Can We Do? Luckily, there are ways we can help stop these invaders in their tracks:

  1. Keep an Eye Out: If you spot any of these plants in your neighbourhood, report it! Learn more on reporting invasives species to the province here >>
  2. Hands-On Help: Sometimes, getting your hands dirty is the best way to fight back. You can help pull out invasive plants or join a community cleanup event to make a difference. Keep an eye out on our events calendar for broom busting and other invasives species community clean ups.
  3. Spread the Word: Tell your friends and family about invasive plants and why they’re a problem. The more people who know, the more help we’ll have in keeping them under control.
  4. Responsible Gardening: If you’re planting in your yard, choose native plants instead of invasive ones. That way, you’ll help create a welcoming home for our local wildlife.

Let’s Team Up! Together, we can protect Sooke’s natural beauty and keep our community safe and healthy. So, keep your eyes peeled for those sneaky invaders, and let’s work together to keep Sooke beautiful for generations to come!


More about Japanese Knotweed and the Sooke River

What is Knotweed and how does it spread?

Japanese Knotweed is a troublesome invasive plant species known for its aggressive behavior. It grows at an astonishing rate of up to 10 cm per day, thanks to its extensive root system that burrows deep into the ground. Unlike many other plants, Knotweed doesn’t have any natural enemies to slow down its rapid growth. It spreads mainly through small pieces of plants breaking off and taking root elsewhere, quickly covering large areas and outcompeting native plants. Along rivers and streams, these plant fragments can easily float away, starting new infestations in different places.

After flowering in July/August, Knotweed turns yellow and goes dormant as winter approaches. Its dried stalks remain visible throughout the winter, marking where it has spread.

Why is Knotweed a problem?

The invasion of Knotweed poses several serious threats:

  • Ecological Disruption: Knotweed grows so fast and thick that it shades out other plants, disrupting the balance of local ecosystems. This harms native plants and animals by reducing their access to sunlight, space, and food.
  • Habitat Damage: Knotweed can take over stream banks, harming habitats vital for fish like salmon. This is especially worrying for the T’Sou-ke Nation, whose culture relies on healthy land and water.
  • Environmental Risks: Knotweed worsens erosion, destabilizes stream banks, and increases the risk of flooding. Its shallow roots don’t hold soil well, leading to more sediment washing into waterways. Plus, its dry stalks can fuel wildfires, making affected areas even more dangerous.
  • Damage to Buildings and Roads: Knotweed’s roots can penetrate through hard surfaces like concrete and asphalt, causing expensive damage to roads, buildings, and other structures.
  • Safety Hazards: Standing up to 2 meters tall, Knotweed can block visibility along roads, making driving risky and causing accidents.
What has Sooke done to control Knotweed?

The District has been working closely with the T’Sou-ke Nation and Capital Regional District for over five years after the specifies was first identified in Charters Creek.

Unfortunately, surveys of the species inform us that we are losing the battle to control the plant in this area and a new approach is needed. The remaining solution is the application of herbicide. Herbicide application requires a Pesticide Use Application Permit from the Ministry of the Environment and Climate Change Strategy. Initial consultation with the Province indicates permit application submission is the next step to addressing the scale of invasive Knotweed in Sooke.

Once the Ministry of the Environment and Climate Change Strategy reviews the District’s application, further steps will be determined.

How can herbicide help? Won’t that cause even more environmental damage?

In the “toolbox” for controlling invasive plants, there are three control options: Mechanical, Biological, or Chemical. The knotweed site conditions (ie. knotweed plant biology, site proximity to infrastructure, effect on surrounding vegetation) influence which control methods is feasible to be used for the proposed knotweed sites.

Mechanical Control:

Knotweed regrows every year from its roots, so mechanical control methods would need to remove the roots to be effective. With a massive root system that can extend up to 20 m across and 3 m deep, the area that needs to be excavated would be very large, and may even include structures like culverts, sidewalks/roads.

Although cutting or mowing methods are also available, trials have shown that it can also stimulate the plant to grow back more aggressively and encourage the roots to grow further and deeper – making the plant even more difficult to control. Further, if mechanical methods are not carried out with extreme caution, it can create many plant fragments which can create even more infestations. With a plant like knotweed that can grow 10 cm per day, many follow-up visits (weekly or bi-weekly) would be needed to catch any new regrowth, which is not feasible.

Cutting, mowing, or digging might be effective for very small (less than 50 stems), isolated infestations that have not established a large root system yet. But the knotweed site that Sooke is hoping to control is not small or new, and would have a very large root system developed already.

Unfortunately, trials which have attempted to use only mechanical methods (ie. only cutting) to control large knotweed sites have not been successful.


Biological Control, or biocontrol, is the use of an invasive plant’s natural enemies – like insects – to reduce the plant population.

Unfortunately, there currently are no biocontrol agents available for the control of knotweed.

Chemical Control: 

The knotweed root system is the growth-centre of the plant where energy is stored, so it is crucial to target the roots in order to provide effective long-term knotweed control. This means that an effective control needs to be absorbed into the roots – herbicides, which can be absorbed by the plants and translocated to the roots, would be an effective control method.

Herbicides need to be carefully applied to prevent any impacts to surrounding vegetation. There are targeted methods of application, such as backpack spraying using a wand, stem injecting, or wipe-on, which would limit the herbicide use only onto the knotweed plants. Additional items or considerations, like using tarps or applying herbicide when adjacent water levels are low, can further help prevent impacts to surrounding vegetation and prevent the herbicide from coming into contact with soil or water.

Currently, herbicide is the only demonstrated control method that has been successful in controlling large knotweed sites. This success requires only two visits per season by timing the treatments when the plant is actively drawing the herbicides into the roots. In fact, a 2010 Oregon State University study demonstrated 80% control of Japanese Knotweed after 1 year of herbicide treatment.

How is the District of Sooke planning to control the Knotweed?

For this knotweed control work, three methods of herbicide application would need to be used: Stem injection, Foliar spray, and Wipe-on. The herbicide glyphosate would be used as it is the only herbicide whose label allows for it to be applied via the stem injection method, which is a necessary application method as depositing the herbicide directly into the knotweed stems can eliminate the risk of pesticide drift away from the plant.

Studies have also shown that glyphosate is non-persistent in soil and water, which means it does not stay active when it comes into contact with soil and water. Instead, it is degraded by microbial organisms (bacteria and fungi). This prevents leaching and uptake from other plants that did not have the herbicide applied to them.

Foliar Spray:  

Herbicide is carefully applied onto the knotweed leaves using low flow backpack or hand-held sprayers and spray wands.

Tarps would be used as herbicide drift shielding precautions to eliminate contact with either non-target vegetation or adjacent water.

Stem Injection:  

Herbicide is deposited directly into the hollow knotweed stems using hand-held injection devices. All stems of the plants would be injected, which requires the stems to be ≥ 0.5” for application to occur.

The risk of pesticide drift should be eliminated due to depositing herbicide directly within the plant.


Herbicide is wiped on the leaves using wick applicators, which consist of an absorbent pad or brush device.

Risk of pesticide drift should be eliminated due to depositing herbicide directly onto the plant.

If the Province approves a permit, when will treatment occur?

The best time to control the knotweed plants is while the plants are actively growing to trans-locate the herbicide into the roots. Given this, it would be anticipated that treatments would take place near September.

In any case, the timing would be adjusted to ensure that work is done outside of the salmon spawning window. Consideration would also be given when water levels are at their lowest.

All treated sites would be re-visited after treatment to monitor and assess the efficacy of initial treatments and re-treated if necessary or possible.