American skunk cabbage (Lysichiton americanus), AKA: Western Skunk-cabbage.
This very distinctive plant has huge leathery leaves between 40cm – 1.5m, and bright yellow flowers (spathes and spadix) up to 45cm, which resemble those of the native but much smaller Lords and Ladies (Cuckoo Pint). Its seeds disperse via waterways, but also probably by birds and animals.
It is found on pond margins, stream sides and wet woodlands. The plant is slow growing and only plants of three years or older produce flowers and seeds.
It was widely planted as an ornamental plant besides ponds and in bog gardens and was still on sale as recently as 2009, it has gradually escaped from gardens and into the wild.
The large leaves and dense stands of the plant lead to it out-competing smaller plants due to its shading effect and can cause extensive damage locally to native flora including vascular plants and mosses. It can grow in shade or full-light and in a range of different soil conditions and thrives in disturbed environments.
Given the popularity of this plant in gardens and its continued introduction into the wild, the problems are likely to increase. Although initial invasions will expand slowly, once this plant takes hold it can spread rapidly and become a serious problem.
We now have multiple reports of it around the catchments of Cleddon/Llandogo, Whitebrook, Brockweir/Hewelsfield and upstream of Coleford.
A large seed bank can build up in the soil and can remain viable for around 8-9 years, so we anticipate we will be seeing American Skunk Cabbage in the lower Wye Valley for at least the next 8-10 years.
With its deep tap roots and rhizomes, chemical control is the recommended option for skunk cabbage, especially for dense stands of skunk cabbage. However, as it usually grows in water or in areas within the water table, only suitably qualified people can undertake this.
We are working closely with our local communities, tapping into the wealth of local knowledge to map locations, which we add to our Geographic Information System (GIS) once we’ve ground-truthed the report. And of course we need to gain landowner consent for access to the sites. We then share this information with our specialist contractors who carry out the appropriate treatment (spraying or stem-injection) for each site.
As a result of our increasing knowledge and by securing further funding in 2020 we scaled up the project from just 1 skunk cabbage site in 2019 to 14 sites. This year we’re extending WISP’s reach to include even more communities and the number of sites has now gone up to around 24 sites currently.
We have carried out a stem-injection trial at 3 sites (in Brockweir and Whitebrook) in 2021 and we will be comparing the results with sites where plants have sprayed and dug up.
Please use our website form to send your sightings to us. These will help us to gain a better understanding of the distribution of this invasive species and strengthen our case for further project funding.
If you are a landowner needing support to control your American skunk cabbage please complete the Landowner Consent form and then hopefully we can add it to our control schedule.
Live-heading – the risk of spread of American skunk cabbage can be reduced by live-heading the flowers before they set seed. It usually flowers in spring, sometimes before leaves appear, with very large, photogenic yellow spathes. If you’re sure the flowers haven’t set seed yet then they can be secure composted (away from watercourses). If there’s a risk they have set seed then dry them out and burn them.
If you have only have a few plants you could try to manually dig them out. From what we’re seeing this isn’t an overly successful method of removal because you must include all underground rhizomes. We have seen one case where not enough care was taken and new plants have readily established from rhizome fragments, growing back more abundantly than before. Care is needed to collect all plant matter if digging it up and plant material must be destroyed through burning or by drying it out (away from watercourses) and secure composting.
Photos courtesy of GB NNSS, Wye Valley AONB team and Emma Drabble.