Exposing the invasive plants that hide in winter
As autumn settles in, you might think your invasive plant problem is dying off with the changing leaves, or you may be feeling safe because you can’t see anything growing that may be an issue. But the truth is far more sinister – lots of invasive plants don’t die in the colder months, they simply slumber underground, waiting for spring to return stronger than ever. These plants are rhizomatous (grow via an underground rhizome system), and include these highly invasive species:
With many invasive plants the above ground system may seem to wither, however its roots (known as rhizomes) are very much alive, storing energy in preparation for the warmer months. To the unprepared, this hidden horror lurking beneath the surface is ready to burst forth with renewed vigour as soon as the weather turns with the new season. Below we show images of these plants before they go underground.
With Japanese knotweed the above ground foliage drops off, leaving dry brittle canes, but we’re seeing spring growth as early as late December – catching many off guard.
The only species from this list that remains visible above ground in winter is Bamboo which may retain its leaves, or it may be reduced to canes, but what you can see is misleading as invasive Bamboo will be ‘running’ underground, spreading metres away and could pop up on neighbouring land or property.
Horsetail is particularly problematic for landowners as it’s not only one that disappears over winter, its highly aggressive root system enables it to spread far and wide. Treatment can be a long-term control project so it’s best to catch it early. A trained surveyor will be able to spot Horsetail and advise on removal options.
Variegated yellow archangel, being one of the shallow rooted species makes mechanical removal a good option, it can be easily dug out of the ground, however it is important to removal all elements of the plant especially the roots.
Parrot’s feather, an aquatic weed is highly invasive, choking water bodies and out-competing native species by blocking out their natural light source. Its dense growth blocks drainage systems and can also cause flooding by impeding water flow. With large scale colonies excavation may be required in order to completely remove any remaining roots systems. As the plant waste is deemed as special ‘controlled waste’ it will need to be taken to a suitably licensed landfill.
Here’s what could happen
- Homeowners can experience issues and often costly delays in property sales.
- Construction and development projects can be put on immediate hold.
- Property management agents could be struck with an untimely addition to their yearly budget.
- Private landowners and estate managers will need to factor in control or eradication measures to avoid encroachment issues.
Why act now?
This is why autumn can be an ideal time to act. Let’s take Japanese knotweed as a key example. In autumn the knotweed plant is sending all its energy from the leaves into its roots ready for storage over the colder months, making it the ideal moment to apply herbicide which will be translocated deep into the rhizome core. Waiting until winter just delays this approach, as the dry brittle canes simply require cutting down. In spring the untreated rhizomes can give rise to more aggressive growth, which will be harder and more expensive to control. With that in mind now is the ideal time to give a few pointers for knotweed identification:
How to identify Knotweed in autumn
Recognising knotweed in autumn can be tricky, but there are some tell-tale signs to watch for:
- Brittle brown canes– In autumn, knotweed stems turn brown, becoming hollow and brittle. They often look like dead bamboo.
- Golden or fallen leaves– The green heart-shaped leaves of summer turn yellow and drop off, leaving behind the distinctive zig-zag pattern of the stems.
- Hollow stems– If you break a stem, you’ll find it hollow, which is a key characteristic of knotweed.
- Clusters of canes– Even though the plant above ground may look dead, you’ll often see dense clusters of canes standing at around 1-2 metres in height.
Use our free identification service to upload photos of the suspicious plant and get expert confirmation.
Don’t wait for a spring disaster
All the rhizomatous plants listed in this article, if left untreated, can cause significant structural damage to homes, driveways, and boundary structures as well as underground infrastructure such as pipes, drains and cables. By acting in autumn, you can get ahead of the problem and save yourself from much bigger headaches down the road. It’s not too late to have a herbicide treatment, and put a full plan in place for next year. Excavation can be carried out all year round – so if complete removal is what you’d prefer, why not get a quote for one of the many excavation options available.
Plan ahead for spring
A proactive approach now will help ensure your development site, land or property’s value isn’t affected by invasive plants when it comes time to sell.