Should You Burn Japanese Knotweed? A Definitive Guide

Japanese knotweed is an invasive plant that can be incredibly difficult to eradicate. With its rapid growth and ability to regrow from even the smallest fragment of root left behind, many homeowners become desperate to get rid of it and turn to burning as an option. However, experts agree that burning Japanese knotweed should be avoided. Here’s why.

What Is Japanese Knotweed?

Japanese knotweed (Fallopia japonica) is a large, herbaceous perennial plant that is native to East Asia It was introduced to Europe and North America in the 19th century as an ornamental plant but quickly became regarded as a problematic invasive species

Some key facts about Japanese knotweed:

• Grows rapidly, up to 10cm per day in the summer. Can reach heights of over 3 meters.

• Spreads easily Even small fragments of root or stem are able to regenerate into new plants

• Has an extensive root system that can reach depths of 2-3 meters underground. The roots can spread laterally up to 7 meters.

• Is very difficult to eradicate. Physical removal must eliminate all root fragments to be successful.

• Causes damage to buildings, pavements, and infrastructure as it grows.

• Reduces biodiversity when it becomes the dominant plant in an area.

• Is classified as “controlled waste” in the UK due to its invasive nature. There are legal responsibilities for proper disposal.

Why People Want to Burn Japanese Knotweed

People turn to burning Japanese knotweed when they become frustrated with failed attempts to control it by other methods such as cutting, digging, or herbicide application. Reasons they may consider burning:

• Burning seems like an easy, low-effort way to get rid of knotweed above ground growth.

• People mistakenly think burning will “kill” the plant so it won’t come back.

• Physical removal feels endless, so burning appears to be a fast solution.

• They want to avoid the use of chemical herbicides.

• Previous Japanese knotweed control methods failed and they hope burning will work better.

• They believe burning will eliminate the need for hauling plant material away.

Unfortunately, none of these reasons make burning an effective strategy for Japanese knotweed control.

Problems with Burning Japanese Knotweed

While it’s understandable why people want to burn Japanese knotweed, there are several problems that make burning ineffective and potentially illegal:

• It doesn’t kill the roots – The extensive underground rhizome system can survive fire and regenerate new growth. Any root sections left behind will lead to regrowth.

• Can spread the plant further – Burning causes the plant’s stems to fragment. These fragments can take root if dispersed by wind or runoff water and spread the infestation.

• Harms other plants – It’s difficult to contain the fire and avoid damage to desired vegetation. The intense heat can damage nearby plant roots.

• Produces air pollution – Burning knotweed creates smoke that can be harmful to health if inhaled.

• Risks causing wildfires – Fires can easily spread out of control, especially during dry conditions.

• May be illegal – There are often laws prohibiting burning weed infestations or requiring permits first. Burn bans may also be in effect.

• Still leaves waste to dispose of – The burnt plant material still must be safely discarded according to Japanese knotweed regulations.

• Can be dangerous – Mistakes in burning can lead to injury or property damage. Even experts caution against DIY burning.

The numerous downsides clearly show that burning does not solve the Japanese knotweed problem. At best, it temporarily gets rid of above ground growth while leaving the underlying root system intact. At worst, it spreads the infestation while creating health and safety hazards.

Burning Japanese Knotweed: What the Experts Say

Organizations specializing in Japanese knotweed control universally advise against trying to burn it as a DIY eradication method. Here are warnings from leading experts:

• “We would never recommend burning knotweed as a method of control…burning does not eradicate all of the knotweed – it will merely leave some black charred holes in the landscape.” – TCM Soil Solutions

• “Burning Japanese knotweed can be an effective way to remove the weed, but there are many hoops you have to jump through to make burning an effective method of eradication.” – Taylor Total Weed Control

• “Burning (even with accelerants) has little effect on the rhizome system below ground so regrowth is rapid.” – Royal Horticultural Society

• “Never ever burn Japanese knotweed. It’s just about the worst thing you can do.” – Environet UK

These organizations agree that attempting to burn Japanese knotweed is not worth the risks and inevitable regrowth. Homeowners are strongly urged to avoid the temptation despite the appeal of a seemingly quick fix.

Proper Removal Methods for Japanese Knotweed

While burning is not recommended, there are methods that can successfully eradicate Japanese knotweed over time:

• Herbicide application – Using glyphosate or other appropriate herbicides weakens the plant and kills the rhizome system when properly applied over several growing seasons.

• Digging out roots – Excavating at least 3 meters down and 7 meters outward from the visible growth can remove the entire root system but is extremely labor intensive.

• Cutting/strimming – Cutting stalks repeatedly during the growing season helps weaken the plant each year. But roots must also be treated.

• Covering – Smothering the plants by burying them under substrates like gravel can be effective over several years.

• Biological control – Releasing plant pests that specifically target knotweed shows promise for managing growth. Still experimental.

Completely killing Japanese knotweed requires depriving the plant of energy in its root system so it cannot regenerate growth. This takes patience and persistence using methods that weaken the roots incrementally over time. Attempting shortcuts with methods like burning rarely provides satisfactory long-term control.