Giant Hogweed

They tower high above our heads with great, sprawling leaves like plants from a long-lost

Jurassic rainforest, obscuring our view from the hillside down to the river. In fact, it was precisely

these captivating aesthetic qualities which brought these Giant Hogweed plants to our shores in

the first place, arriving as an ornamental plant from Central Asia for adorning the botanical

gardens of 19th Century plant enthusiasts. From these gardens it escaped, if we can call it that,

into the wider landscape thanks to its alarmingly virile nature - single plants can produce

between 30,000 and 50,000 seeds annually which can survive for up to 15 years before

germinating. The plant’s preference for damp riverside habitats offers it easy access to conduits

for spreading these seeds, which travel downstream in the currents of the rivers and streams

crisscrossing this country. The River Lox which cuts through Maple Farm, a great ecological

asset of the rewilding project, unwittingly brought these stowaways onto the site, where they’ve

gleefully colonised much of the bankside habitat. Growing in dense patches, the hogweed

shades the ground beneath it in the spring and outcompetes other plants, reducing biodiversity.

That’s not great news for us, trying as we are to create the conditions for a great diversity of

native species at Maple Farm.

That term - native - and its ecological opposites - non-native, invasive, alien - brings us into

some shady territory when it comes to species considered to be in or out of place in a

landscape. The kinds of aggressive language and tactics we use to demonise and eradicate

these species can evoke a kind of ecological xenophobia that we want to steer well away from.

This said, understood purely in terms of its specific ecological impacts, we can say quite clearly

that the hogweed presents a problem for the plant, invertebrate, and animal communities at

Maple Farm and for the objectives of our rewilding project. So, following on from Colleen’s

existing management efforts before we started this partnership, we decided early on that we

needed to do something about it. As part of our long-term commitment to restoring nature on the

farm, one of our core aims has become to remove, as much as possible, the Giant Hogweed from the site.

There are many ways to go about getting to this point, and as we’ve discovered all of them have

their own drawbacks. One of the most popular solutions is an approach of

chemical warfare using readily available herbicides like glyphosate. Spray, spray, spray and

hope for the best, is what many online guides for hogweed removal will tell you. The issue with

this is that these herbicides can have unintended ecological effects beyond the target plant,

killing other kinds of plant life and affecting other animals, particularly if they enter a water

course where they can be deadly to forms of aquatic life. Another option is manual control. By

cutting off the flowering heads of the plant before they come to seed, it can be possible to

prevent the further spread of hogweed and eventually kill the existing plants. Whilst their roots

are relatively resilient to this kind of approach, eventually their energy stores are depleted to the

point where they cannot grow anymore. This approach is time and energy intensive and

requires extreme care. Giant Hogweed is sometimes referred to as the UK’s most dangerous

plant, because its sap can cause severe, long lasting skin irritations and sensitivity to light. So,

as much as we might like to, one can’t just charge in and start cutting the hogweed. Specialist

protective equipment - suits, gloves, boots and a visor - is necessary. A third approach is

grazing using available livestock, which can stop the hogweed from growing to its flowering

stage. However, livestock can’t get everywhere - the steep bank sides of the River Lox and the

scrub on either side act as barriers to livestock, which can’t therefore reach every plant. A fourth

approach, which we find particularly promising, is hot water treatment. In essence, this works in

a similar way to chemical treatment, but without the harmful chemicals. The hot water kills the

plants when sprayed onto them, it can be sprayed with high precision and so minimises the

effects on the wider ecosystem, and with repeated application this can effectively eradicate the

hogweed plants. Other European countries, like the Netherlands, have achieved great

successes in controlling Giant Hogweed and other invasive plants using this approach.

Unfortunately, this way of treating plants is in its relative nascency in the UK, and there are

relatively few contractors to choose from. As we’ve found out from experience, this can mean

being charged an awful lot of money and receiving a relatively poor service!

In line with our experimental approach to rewilding more generally, we’ve tried a mixture of the

above approaches, and are constantly searching for new ideas for ways to control the Giant

Hogweed we have on site in the least ecologically damaging ways possible. A growing number

of people and organisations are turning away from the default use of pesticides for invasive

species control, which we strongly support. But, in order for this to be as effective as possible,

rewilding organisations and other land managers need to cooperate with each other, sharing

expertise, ideas and resources. With enough demand, and support from sources like local

governments, we can also stimulate the emergence of new companies that offer cutting-edge

approaches like hot water and foam treatments at more accessible rates and with a higher

quality of service. We’ve seen some very positive results from our mixed methods approach so

far, and are always keen to hear about the experiences of others, so get in touch if you have

any thoughts or ideas.