Identifying And Dealing With Japanese Knotweed

Japanese Knotweed (scientific name: Fallopia Japonica) can pose a serious threat to any piece of property, particularly one that's up for sale. All too often, you discover Japanese Knotweed when the mortgage surveyor finds it. This can hold up a sale, lead to price renegotiation, or even spoil the deal entirely.


Our guide will help you learn how to spot Japanese Knotweed and give you some useful guidance on what to do about it if you find it on your property or on a property you're considering buying.

Identifying Japanese Knotweed


Japanese Knotweed goes through major changes in appearance as it progresses through its growing cycle, and this makes it tricky to spot.

In the spring, look for asparagus-type shoots. These are red or purple at first, turning green as they grow rapidly into bamboo-type stems.

In summer, knotweed reaches its full growth height, which can be up to nine feet. Knotweed spreads rapidly and is easily capable of pushing through cracks in asphalt, concrete, drains, and even cavity walls.

By late summer, the plant starts producing flowers. These come in small and cream-colored, emerging from clusters of spiky stems. Japanese Knotweed puts out flat, bright green leaves which are often heart or shovel-shaped.

As the weather goes cold in autumn, knotweed will shed its leaves and the stems turn brown. Knotweed is dormant through the winter -- but if untreated, it will be back the following spring.

If you are at all uncertain about identifying knotweed, seek expert help. Many landscaping and plant care companies will be able to confirm or deny a knotweed diagnosis simply from a photograph shared online.

What Threat Does Knotweed Pose?

When it first gets a toehold, Japanese Knotweed doesn't look any more threatening than any other unwanted weed. Don't be lulled into a sense of complacency! This plant can spread rapidly and cause significant damage. Knotweed's greatest asset is its extremely robust root system. Roots can sink nearly 10 feet deep and extend up to 10 feet to the side.

If you strongly suspect the presence of Japanese Knotweed, as a buyer or a seller, it's a good idea to have the property surveyed by a plant-care specialist like Environet who can provide a cost estimate for eradicating the plant. This cost can be negotiated as a discount on the asking price of the property.

Japanese Knotweed is hardy and strong enough to cause significant damage to a property as it seeks to reproduce itself. The plants can attack expansion joints in concrete paving, damage the mortar between bricks, intrude into cavity walls, and choke drains and pipes.

In most residential infestations, Japanese Knotweed is spotted and addressed before it can cause structural damage to the home. Damage is still possible, and it becomes more likely with properties that are unoccupied and thus less closely monitored

How Does A Site Survey Work?

Any professional that handles unwanted plat eradication should be able to provide a fairly straightforward quote for the eradication of an ordinary residential infestation. In most residential cases, an expert can provide an accurate quote simply from photographs documenting the conditions on-site.

On larger properties and commercial/industrial sites, it's more common for a plant control contractor to inspect the site in person before preparing a quote.

How Is Japanese Knotweed Eradicated?

While the ideal solution for a Japanese Knotweed infestation depends on the specifics of the property, the budget and timeframe available, and what future use is intended for the site, eradication options ultimately come down to two approaches. The plants can either be physically removed or killed in situ with herbicides.

A professional can accurately balance the needs of the property and the wishes of the owner to pick out the most effective way to address the plant problem.

Can A Property Be Sold Without Treating An Infestation?

While buyers and sellers may be willing to go ahead with a property sale when Japanese Knotweed is an issue, the same cannot be said for the financial partners that take part in almost all sales. It is sometimes difficult to secure financing for purchasing or developing a piece of property with an untreated knotweed infestation.

Banks and other lending institutions will generally be satisfied as long as a documented treatment plan is prepared and executed by an appropriate professional. It's best to address knotweed sooner rather than later to prevent delay-causing hassles in the property sale process.

Is Japanese Knotweed Eradication Guaranteed?

Most professionals that can take care of Japanese Knotweed for you will offer some sort of guarantee. Read your contract carefully to review all of the terms of the guarantee, though; many contractors' guarantees lack the insurance backing to provide full financial restitution.

It's very important to comply with the post-treatment guidelines provided by the contractor. Incautious activity (for instance, disturbing herbicide-treated soil too soon) may void whatever guarantee or warranty is offered on the work.

Does Japanese Knotweed Come Back?

Minor regrowth is always a possibility, but post-treatment guidelines should detail how to keep the plant from regaining a serious foothold on the property.

About the Author Laura Bennett

Hello, I’m Laura Bennett. I love nature especially when it comes to flowers and different kinds of plants. I started a very small garden behind my house and I named it Humid Garden. So, I created this blog to provide aspiring and inspiring thoughts about gardening for gardeners and anyone who has the intention of keeping a garden.

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