The root of the problem

The root of the problem

Giant Hogweed (c) Antetixux21

With names that wouldn’t be out of place in a Harry Potter novel, meet some of the UK’s most persistent plants! John tells us how to spot them, and what to do once you have...

Giant Hogweed

Towering at 5m tall - with serrated leaves the size of dinner plates - this is a truly imposing plant.

History - Native to the Western Caucasus Mountains in Southern Russia, it was first introduced to the UK as an ornamental plant in 1820.

Ecology - Individual plants can produce in excess of 10,000 seeds which can be transported by wind, water and humans.

Impact - Often found along riverbanks, it dies back in winter leaving large areas exposed to erosion which can contribute to flood risk.

How do we tackle it? - It must be treated with a suitable herbicide which is applied using a knapsack sprayer, or preferably to the stem using an injector for better control.

What can I do? - Keep your distance! Giant hogweed produces phytotoxic sap which can cause blistering to human skin when exposed to sunlight.

Giant hogweed

Giant Hogweed (c) Antetixux21

Himalayan Balsam

Up to 2.5m tall with a hollow, succulent stem and a pink parade of flowers, this annual plant is distinctive.

History - Native to the central and western Himalayas, it was introduced to Kew Gardens in 1839 but was recorded in the wild by 1855.

Ecology -  An individual plant can produce in excess of 800 seeds. Seed capsules explode when disturbed and project seeds up to 7m in all directions!

Impact - The plant often forms large carpets which outcompete many native plants. It also dies back over winter, leaving riverbanks exposed to erosion.

How do we tackle it? - As well as coordinating surveys, we host a series of ‘Balsam Bashing’ task days where volunteers can lend a hand.

What can I do? - Join in our ‘Balsam Bashing’! Great fun and a huge help - go to for more info.

Himalayan Balsam

Himalayan Balsam (c) GBNNSS

American Skunk Cabbage

A tall yellow flower with large leathery leaves and a strong odour - this exotic is obviously not from our shores.

History - Native to Western North America, it was first introduced to the UK in 1901 as a garden ornamental.

Ecology - Often found in wet woodland and boggy ground. Individual plants can regenerate from fragments of broken stem, dispersed by machinery or by water during floods.

Impact - As its community grows, it begins to crowd out native species, particularly rare and fragile mosses and lichens.

How do we tackle it? - We’re delivering a volunteer-led project to record the distribution of this species. This will consist of hand removal in priority locatons and the replantng of impacted areas.

What can I do? - If you see it anywhere in Yorkshire then please get in touch:

American skunk cabbage

American Skunk Cabbage (c) RPS Group PLC

Japanese Knotweed

With bamboo-like stems up to 2m tall and large green leaves, Japanese knotweed grows in dense stands and has an extensive root system.

History - Native to Japan, Taiwan and Northern China, it was first introduced into the UK in 1886.

Ecology - In the UK, all plants are sterile male clones which do not produce any viable seed. Japanese knotweed is thought to be one of the largest single organisms in the world and it spreads easily from fragments of the stem.

Impact -  If left uncontrolled, it can become very dominant along river corridors and outcompetes many native species and disrupts habitats. Due to its extensive root structure (which can extend down 3m and sideways 7m), it can also cause problems in urban areas - partcularly to building foundations. It’s now a requirement to report it on a property before selling, and to prevent it spreading onto neighbouring land.

How do we tackle it? With a ‘headwaters down’ approach: we tackle the most severe infecton on a watercourse and work systematically downstream.

What can I do?
If you are interested in becoming a volunteer survey or please contact

Japanese knotweed

Japanese Knotweed (c) John Cave