How to Get Rid of Japanese Knotweed

Japanese knotweed (Fallopia japonica) is an invasive plant species that can be very difficult to eradicate. This stubborn weed spreads rapidly and can cause damage to property, gardens, and local ecosystems. Getting rid of Japanese knotweed requires persistence, patience, and the right techniques. Here is a comprehensive guide on identifying Japanese knotweed, understanding its growth habits, and using integrated pest management to control and remove it.

What is Japanese Knotweed?

Japanese knotweed (Fallopia japonica) is a large, herbaceous perennial plant that forms dense clumps reaching heights of 10 feet. It has hollow, bamboo-like stems with raised nodes and distinctive shovel-shaped leaves. The small greenish-white flowers bloom in late summer and are followed by small winged fruits that contain triangular seeds.

Native to East Asia, Japanese knotweed was introduced to North America and Europe in the 19th century as an ornamental plant. Unfortunately, it readily escaped cultivation and is now considered an aggressive invasive species in many areas. Its rapid growth crowds out native plants and damages pavement, foundations, and retaining walls.

Identifying Japanese Knotweed

Properly identifying Japanese knotweed is the first step toward controlling it. There are a few key characteristics to look for:

Hollow Stems and Nodes

The stems resemble bamboo and are light green, smooth, and hollow between the nodes or jointed segments.

Shovel-Shaped Leaves

The leaves are shovel-shaped with a flat base and pointed tip. They alternate along the zig-zagging stems.

Late Summer Flowers

Small clusters of creamy white flowers bloom in late summer. They are often hidden by the foliage.

Spreading Rhizomes

Japanese knotweed spreads vigorously via its system of underground rhizomes. These reddish-brown roots can extend 23 feet laterally and up to 10 feet deep. Even small fragments can generate new plants.

By positively identifying Japanese knotweed, you can take steps toward removing it before it gets out of control. Contact local agricultural extensions if you need assistance with identification.

Understanding Japanese Knotweed’s Growth Habits

To control Japanese knotweed, it’s important to understand its growing habits and life cycle:

It sprouts from rhizomes in early spring, grows rapidly through spring and summer, and flowers in late summer.
The plant dies back each winter and regrows the following spring unless the rhizomes are destroyed.
New stems can emerge up to 20 feet from the parent plant.
Any small fragment of root or stem material can generate a new infestation if left in contact with soil.
It prefers full sun but also tolerates shade, growing in disturbed soils near waterways, roadways, buildings, and gardens.
Once established, the extensive root system is difficult to fully eradicate.

Knowing the life cycle and how Japanese knotweed spreads allows you to time management efforts at the most effective times.

Dangers of Japanese Knotweed

Neglecting to control Japanese knotweed can lead to some significant problems:

It grows and spreads quickly, crowding out native plants in wild areas.
The dense stands of canes block sunlight from reaching other plants.
It poses dangers to building foundations, pavements, walls, drainage systems, and other structures.
It can degrade properties and make them difficult to sell.
Removing large, established patches is extremely labor intensive and expensive.
The plant dies back each winter, leaving shorelines more vulnerable to erosion.
Property values can decline due to unchecked infestations.
Japanese knotweed does not provide much food value for wildlife.

Catching knotweed infestations early helps avoid severe impacts to ecosystems and properties.

Getting Rid of Japanese Knotweed

Eradicating Japanese knotweed requires an Integrated Pest Management (IPM) plan that combines multiple control and removal techniques for the best results. Persistence and patience will be needed.

Prevention

Preventing Japanese knotweed from establishing in the first place is the best defense. Take these preventive actions:

Learn to identify Japanese knotweed and do not plant it.
Use only fill dirt, gravel, and other materials that are known to be weed-free.
Clean equipment, boots, and tools thoroughly after working in knotweed infested areas.
Monitor routinely for early detection of new sprouts or spreading patches.
Encourage and plant native species to compete with knotweed.

Early detection and removal of new sprouts is key for prevention of larger infestations.

Manual Removal

Manually digging up and removing young Japanese knotweed plants can be effective for small areas. Take care to remove all roots and rhizomes or regrowth will occur.

Steps for manual removal:

Using a shovel, hand trowel, or similar tool, dig down at least 3 feet around the plant.
Carefully shake or rinse soil from the roots over a tarp to contain plant parts.
Thoroughly search for any root fragments and remove them. Even 1-inch pieces can resprout.
Place plant parts in thick contractor garbage bags for disposal. Do not compost.
Monitor the site routinely for any regrowth for several years after removal.

Manual removal can be successful but is labor intensive. Any root fragments left behind will generate new growth.

Cutting and Mowing

For larger infestations, repeatedly cutting back the canes and foliage can incrementally weaken Japanese knotweed over time. But this method alone usually does not eradicate infestations.

Tips for cutting:

Use a brush cutter, mower, or handheld clippers to cut canes close to the ground 2-3 times per growing season.
Time cuttings just as the plants reach about 3 feet tall. This will deplete root reserves.
Cuttings must be done repeatedly for several years to exhaust the rhizomes.
Removing cut canes helps prevent resprouting but is not mandatory.
Monitor closely for any regrowth and cut again.
Herbicide application improves results when paired with cutting.

Frequent cutting damages rhizomes and works best when integrated with other methods. But regrowth will occur if cuttings are skipped.

Herbicide Application

Applying certain systemic herbicides can be very effective at killing Japanese knotweed. Glyphosate products work well when applied correctly.

Herbicide application guidelines:

Consult local regulations on herbicide use and use only as directed.
Apply to actively growing foliage in spring or summer, avoiding flower pollination times.
Thoroughly wet all foliage but avoid runoff into waterways or drains.
Glyphosate products require translocation to the roots for best results.
Follow-up applications are typically needed for several years.
Hire trained professionals for herbicide application on large areas.
Monitor for regrowth and re-apply as needed.

Herbicides work best when combined with other methods like cutting or digging. Always use according to label directions.

Smothering With Mulch or Tarps

Smothering Japanese knotweed is another option, using materials like wood chips, gravel, tarps, or geotextiles placed over the infested area. This blocks sunlight and suppresses growth.

How to smother knotweed:

Mow or cut existing canes close to the ground first.
Place a 4- to 6-inch layer of mulch, gravel, or other material over the area. Use more for tarps or fabric.
Extend the material well beyond the infested area to block growth.
Leave in place for at least 2 full growing seasons.
Monitor edges for any new sprouts and maintain material depth.
May take multiple seasons of smothering based on rhizome depth and vigor.

Proper mulching technique kills Japanese knotweed without chemicals. But adequate time and material depth are needed.

Professional Help for Removal

For severe Japanese knotweed infestations, professional weed control specialists have the training, equipment, and herbicides to remove it. Seeking professional help can be wise in certain cases:

If the infestation is large or covers rugged terrain unsuitable for DIY work.
If herbicide application is needed beyond your capabilities.
If total eradication is critical due to potential impacts.
If the infested area cannot be adequately monitored after treatment.
If access to the site is challenging.
If required by local authorities or property owner/community associations.

While expensive, professionals can tackle the most challenging knotweed infestations when needed. Get estimates from qualified contractors.

Proper Disposal of Knotweed

To avoid further spread, it’s critical to properly dispose of all parts of Japanese knotweed after removal:

Do not compost any portion of the plant. It can survive and spread from compost heaps.
Place plant parts in thick plastic contractor bags for disposal. Double bagging is recommended.
Dispose of at designated waste management facilities or landfills, not in home waste bins.
If burning is allowed in your area, incinerate the bags and bury the ashes.
Never discard pulled plants or cut canes in natural areas or waterways.
Clean tools, boots, and vehicles that contacted knotweed to prevent spread.

Carefully containing and discarding all knotweed waste is just as important as removal. Follow local regulations.

Ongoing Management of Knotweed

Completely removing Japanese knotweed requires dedication over multiple seasons. Here are some tips for ongoing management:

Routinely monitor sites for several years after treatment and quickly remove any new sprouts.
Re-apply herbicides or do additional digs as needed. Knotweed rhizomes are stubborn.
Use native plants or non-invasive groundcovers for restored areas to suppress knotweed regrowth.
Do not excavate or disturb treated areas unnecessarily. This can uncover rhizomes.
Keep construction materials, top soils, and fill dirt weed-free when improving sites.
Clean equipment, footwear, and vehicles thoroughly after working in infested areas.
Dispose of waste properly and monitor local composting sites.
Water and promote healthy native plant communities that can outcompete knotweed.

Staying vigilant and using integrated techniques leads to the best results for keeping Japanese knotweed controlled.

Dos and Don’ts of Removing Japanese Knotweed

Do:

Correctly identify Japanese knotweed before taking action.
Use integrated control methods for best results.
Dig up small patches carefully and dispose of properly.
Cut back larger patches repeatedly.
Cover infested areas with mulch, gravel, or geotextiles to smother growth.
Use glyphosate and other herbicides with caution as directed.
Monitor treated areas for several years for any regrowth.
Promote native plant species to suppress knotweed.

Don’t:

Confuse Japanese knotweed with similar native species like phragmites.
Attempt to just pull up or yank large plants without digging out the roots.
Allow cut canes to grow into waterways where they can spread.
Place pulled Japanese knotweed plants into compost piles.
Burn Japanese knotweed as a means of disposal unless permitted.
Spread excavated infested soil to uncontaminated sites.
Assume one treatment will eliminate the weed; plan for ongoing management.

By following some key dos and don’ts, your Japanese knotweed control efforts will have greater success. Removal takes perseverance.

When to Seek Professional Help

Consider reaching out to qualified invasive plant management professionals if:

The infestation covers over 2500 square feet.
Dense patches are located on steep slopes or challenging terrain.
Herbicides can’t be applied safely by hand without risk of non-target damage.
You are unable to commit to the proper multiple-year management timeline.
Local regulations require professional abatement.
The plant is posing immediate risks to property, drainage systems, foundations, or valuable landscaping.
Total eradication of the weed is critically important due to impacts.

Don’t hesitate to seek expert help when Japanese knotweed escapes your control. Paying for pros can save headaches and expenses down the road.

Control Methods Summary

For starters, correctly identify Japanese knotweed before taking any control measures.
Focus on prevention by avoiding contaminated soils and removing new growth promptly.
Manual digging can work for small infestations if done repeatedly and thoroughly.
Cutting alone weakens Japanese knotweed but multiple treatments are needed.
Herbicides provide knockdown but follow-up applications are key. Use as directed.
Smothering with mulches, gravel, or geotextiles also suppresses growth over time.
Properly dispose of all plant parts – do not compost or discard where they can spread.
Be ready to use control methods persistently over several seasons. Eradication takes dedication.

A strategic Integrated Pest Management approach offers the best chances of success against Japanese knotweed.

Frequently Asked Questions

What makes Japanese knotweed so hard to get rid of?

The extensive root system with deep rhizomes makes Japanese knotweed difficult to eradicate. Any left behind root fragments can generate new growth. It also grows back vigorously when cut or mowed. Complete removal of the root network is challenging.

Does cutting down Japanese knotweed help?

Cutting alone will not eliminate Japanese knotweed but it does weaken the plant incrementally when done repeatedly over several seasons. Cutting is most effective when combined with other treatments like herbicide application or digging. But consistent monitoring and additional cuttings are needed for best results.

What is the best weedkiller for Japanese knotweed?

Systemic glyphosate herbicide products are considered most effective for controlling Japanese knotweed. They are applied directly to the foliage. The key is allowing time for the herbicide to translocate down to the root system below ground. This takes several weeks. Repeat applications are almost always needed. Always follow product label directions carefully.

Does vinegar kill Japanese knotweed?

Using horticultural vinegar with higher acetic acid concentrations can damage Japanese knotweed leaves and stems. However, it does not kill the root system so regrowth will occur. Homemade vinegar weedkillers also lack the strength needed for controlling knotweed. So while vinegar may suppress some growth, it won’t eradicate Japanese knotweed on its own.

Does sea salt kill Japanese knotweed?

Applying sea salt directly to Japanese knotweed may damage and dry out the foliage it contacts. But it has no effect on the root system or rhizomes underground. New growth will emerge and the salt does not translocate to the roots. Therefore, sea salt alone has very limited effects and should only be considered an addition to other more effective treatments. It does not kill the weed outright.

Does Japanese knotweed damage foundations?

Yes, Japanese knotweed poses some risks to foundations when growing in close proximity. Its vigorous root system can exploit cracks and weaknesses in foundation materials. This can lead to structural damage over time if not controlled. Newly sprouted knotweed near foundations should be promptly removed and monitored to prevent damage. Established stands near structures may require professional removal.

Conclusion

Japanese knotweed may seem invincible, but a well-planned, systematic approach using IPM techniques can produce results and prevent regrowth. The key is persistence and repeating certain methods like cutting and herbicide application over several seasons. Prevention is also paramount – avoid introducing contaminated soils and remove sprouts before they spread. With dedication, Japanese knotweed can be successfully eliminated, or at least adequately controlled and suppressed to minimize impacts. Don’t allow small infestations to spiral out of control. Seek professional help when needed for severe infestations. Despite the challenges, you can reclaim your property from Japanese knotweed with time and effort.