What should I do If I find Japanese Knotweed?

What is Japanese Knotweed?

Japanese Knotweed is an invasive, non-native plant that if left unchecked can cause havoc in your garden. Unfortunately because it grows so easily and is so hard to eradicate, there are rules and regulations that need to be followed when dealing with it.

How to identify the plant:

The first thing to note is that Japanese knotweed looks different at different times of year depending on its growth stage.

Spring

In spring you will see reddish purple asparagus-like shoots with light green leaves sprouting from the ground. They will come up around other plants, but in time will suffocate their competition and steal all the nutrients from the soil.

Summer

Summer is when the plant will grow at its peak. The stems will grow tall with distinctive ribs and veins. The leaves will get darker green and small white-ish cream flowers grow in clusters around the stem.

Autumn

Towards the end of summer moving into the autumn the leaves will turn yellow and wilt. At this point the stems will be approximately 2-3 metres tall and will change to a dark brown.

Winter

In winter the plant will die off, and lay dormant until the spring when new sprouts will shoot and the whole cycle starts again.

Why is it so problematic?

Because of the rapid growth cycle, the Japanese Knotweed can be very destructive to not only the other plants in your garden, but can also cause structural damage to your building too. If not treated (and kept treated) the roots can grow three metres deep and seven metres wide.

It might even find weak spots and cracks in concrete to grow through, and could damage integral parts of your brickwork.

If it causes structural damage or if it’s on your property and you don’t disclose that it’s there, it can land you in all sorts of trouble when selling your property.

So how do you treat it?

There are a few options when treating Japanese Knotweed.

Cultivation Methods

Although digging up the roots would be effective in getting rid of the plant, there are some issues with taking this approach.

Disposal - As the plant is classed as a ‘controlled waste’ substance under the Environmental Protection Act 1990, you are only able to dispose of the remains at licenced landfill sites.
You must make sure that any contractors that are involved with the removal of the remains are registered waste carriers.
It's extremely difficult, even the smallest piece of root left in the ground will produce a new Japanese Knotweed plant.

Burn

To dispose of Japanese Knotweed by burning, you will first need to check with your local council that this is allowed, then dry out the remains before burning them. You should also follow the guidance on how to bury the burnt materials, as some rhizomes or the crown of the plant can survive burning and therefore need to be disposed of properly.

For businesses you need to tell the Environment Agency one week or more before you burn the remains and the Environmental Health Officer at your local council.

Spray with Chemical weedkiller

As a home gardener you could use a Glyphosate based weed killer to treat the plant. There are many brands that use this substance and it may take 3-4 sessions to completely treat the affected area.

Chemicals should be used with extreme caution and only as advised on the packet.

However, the risk with this is that you could cause lots of damage to your surrounding garden, so it’s widely recommended that you work with a professional who may have access to stronger weed killers, but who will also be trained properly in how to use them.

The treated plants will often produce bushy regrowth, different in appearance. The regrowth must be retreated.

Call in the professionals

Sometimes, if it’s a large problem it will be worth calling in the professionals to help treat and remove the plant and roots. Most registered companies will be backed by a transferable guarantee for any work carried out, which will help you when you come to sell your property. Some mortgage lenders require assurances that it will be eradicated before agreeing the funds so having a management plan by a registered eradication company will help.

Disposal

No matter what your method of removing Japanese Knotweed, you need to make sure you dispose of any waste properly. This means you can’t just throw it in the garden waste or general waste bins. You must make sure that the landfill site you use is licenced to take that kind of waste.

Incorrect disposal of Japanese Knotweed could result in being fined up to £5000 or up to 2 years in prison.

Any company you use to dispose of the plant remains, you will need to make sure they operate within the conditions of the ‘treatment of invasive non-native plants: RPS178’ and have the relevant permit to dispose of it.