The Injurious Five: Britain's Outlaw Wildflowers

On a warm afternoon in late July, walk the edge of almost any rough field, verge or railway bank and you will find a plant that the law of the land would call a weed. Common ragwort stands waist high, its flat-topped blaze of yellow flowers loud against the drying grass. Look closer and the flowers are busy: hoverflies, solitary bees, soldier beetles, the odd gatekeeper butterfly.

And on the leaves, if you are lucky, a row of caterpillars in black and gold hoops, feeding shoulder to shoulder with the confidence of something that knows it tastes terrible. These are cinnabar moth larvae, and the ragwort is the only real home they have.

Then the strimmer arrives, or the sprayer, or the volunteer work party with gloves and bin bags, and the whole small ecosystem is gone in an afternoon (I can never help but think of Dr Suess's ''Horton hears a Who'' here, where, without the littlest 'Who' in 'Whooville' - a fictitious town on the head of a dandelion - adding his voice and making sure their home was not destroyed, the ''Whos of Whoville'' would have gone much the same way as the cinnabar moth caterpillars.

That scene plays out across Britain every summer, and it rests on a word: injurious. Five native wildflowers carry that legal label, and the assumption that follows it is that a good landowner removes them. A study from the University of Sussex recently asked a simple question about that assumption, and the answer is worth sitting with. This piece will give you both halves of it: the surprising value of these plants, and the honest reasons the "injurious" label was not simply invented out of spite.

What "injurious" really means

The word comes from the Weeds Act 1959, which names five species as injurious to agriculture: common ragwort, creeping (or field) thistle, spear thistle, broad-leaved dock and curled dock.

Growing ragwort in your garden is not an offence, and never has been. What the Act in fact does is give the relevant authority, now Natural England, the power to serve an enforcement notice on the occupier of a particular piece of land where these weeds are spreading onto agricultural ground. Only once such a notice has been served does any legal obligation arise, and failing to comply with a served notice is the offence, not the plant itself. The Ragwort Control Act 2003 is widely misunderstood. Despite its name, it did not ban ragwort, did not create a duty to control it, and did not make growing it a crime. It did one thing: it allowed the government to publish a Code of Practice on preventing ragwort's spread, which appeared in 2004. The rule that ragwort must be cleared within 50 metres of grazing land comes from that code, not from any statute, and it is guidance rather than law. Tellingly, the Welsh version of the guidance, (I just googled it because I happen to be staying in Llandeilo with my children at the moment revisiting the holiday easapces of my own childhood) uses 35 metres instead.

None of this is trivial, because a great deal of money and effort flows from the misunderstanding. Balfour and Ratnieks used freedom of information requests to estimate that public bodies such as local councils, Natural England and Highways England spend in the region of £10 million a year controlling injurious weeds. Ragwort in particular is often lumped in with aggressively invasive non-native plants like Japanese knotweed, which is a different problem altogether.

The disproportionate value

The Sussex study, published in the Journal of Applied Ecology in 2022, set the injurious weeds against the plants that Defra recommends and funds for pollinators under agri-environment schemes, species such as red clover and wild marjoram. The researchers combined a field survey at six pasture and former-pasture sites in East Sussex with an analysis of two national databases.

Three of the five injurious weeds are insect-pollinated: common ragwort and the two thistles. (The two docks are wind-pollinated, so they do little for nectar-seeking insects, though they still feed a range of herbivorous ones.) Those three weeds, the study found, produce on average around four times more nectar sugar than the Defra-recommended plants, and they draw pollinators in far greater abundance and variety. Their open, composite flower heads act like a public bar rather than a members' club: short-tongued and long-tongued insects alike can reach the reward.

The database evidence is just as striking. In the Database of Pollinator Interactions, which pools records from across the country, the three insect-pollinated weeds had been visited by roughly four times as many pollinator species, and five times as many conservation-listed species, as the recommended plants. Out of 387 plants ranked in that database by the number of pollinator species recorded on them, creeping thistle came fourth, ragwort sixth and spear thistle thirteenth. In a separate database of insects and their food plants, the five injurious weeds supported around twice as many plant-eating insect species as the recommended list. And the plant that supported the most conservation-listed insect species of all, in this study, was the one councils most often pull up: ragwort.

The arithmetic is uncomfortable. The four pollinator-targeted options Defra pays farmers to sow cost the public purse more than £40 million a year, while the plants that outperform them are the ones we spend a further £10 million a year removing. As the paper's authors put it, current policy encourages neither leaving land for weeds nor sharing land with them.

The cinnabar's gamble

To feel why this matters, follow one insect. The cinnabar moth is a day-flying species with crimson-marked wings, named after the red mineral once ground for artists' paint. Its caterpillars feed almost entirely on common ragwort, straying only occasionally onto other ragworts and groundsels. They eat the leaves, absorb the plant's poisons, and turn that theft into armour: the black-and-gold stripes are a billboard warning every bird in the hedge that this particular meal will make them sick.

Pull out the ragwort and you pull out the moth. The cinnabar is listed as a UK priority species, and there is real concern about its long-term trend, though here the honesty principle earns its keep. The moth's numbers swing wildly from year to year, booming when ragwort is plentiful and crashing when hungry caterpillar broods strip their food plant bare, so a bad year is not proof of decline. Reported long-term losses are large but vary a good deal between sources and time periods, and Butterfly Conservation still classes the moth as common rather than rare. The fair summary is that the cinnabar is not on the brink, but that removing ragwort wholesale across a landscape takes away the one thing it cannot do without. Ragwort feeds many others too, from solitary bees to specialist flies and beetles, dozens of insect species in all, some of them nationally scarce.

An honest reckoning

Now the other half, because a series that only ever tells you weeds are wonderful would be no more trustworthy than the one that tells you to spray them.

Ragwort really is poisonous. This is not a myth got up by tidy-minded farmers. The plant contains pyrrolizidine alkaloids, and when a horse or a cow takes in enough of them the liver converts them into compounds that damage it slowly and cumulatively, often with no obvious signs until the harm is done and irreversible. The danger is real, and for anyone keeping horses it is worth taking seriously.

But the shape of the risk is specific, and the specifics change what a sensible response looks like. Living, growing ragwort is bitter and unpalatable, and grazing animals with decent pasture almost always leave it alone. The serious poisonings tend to happen in two situations: when the plant is dried in hay or silage, where it loses its bitterness but keeps its toxicity and can be eaten unnoticed, and when animals are so short of other forage that they resort to it. Buglife's summary suggests a horse would need to eat something like seven per cent of its body weight in ragwort to reach a lethal dose. That is a real hazard managed through hay and grazing, not an argument for clearing every yellow flower from every verge in Britain.

The thistles deserve the same even hand. Creeping thistle in particular spreads aggressively by underground roots as well as seed, and a farmer trying to keep a productive field has a legitimate reason to control it. The word injurious was not pure hysteria; on the wrong ground, at the wrong scale, these plants do cost people money. The error is not the control, it is the blanket. Treating a plant that is a problem in a hay meadow as a problem everywhere, including the road verge, the waste corner and the conservation site, is where the policy and the science part company.

And the scale cuts the other way too. One tolerated ragwort plant in one suburban garden is, on its own, a modest thing. The value in this story is collective: it lies in a whole country deciding not to sterilise every rough margin, so that the plants which quietly outperform our sown wildflower mixes are allowed to keep doing their work.

What this means in your garden

Start with your situation, not a rule. If you keep horses, or your patch adjoins grazing land or a hay field, take ragwort near those animals seriously and remove it there. If you do not, and most suburban gardeners do not, the legal and practical pressure to clear it largely evaporates. You are allowed to relax.

Leave a little, in the right place. A few ragwort plants in a rough back corner, well away from any grazing, will feed late-summer pollinators and may host cinnabar caterpillars. This is late-season nectar, arriving when many spring flowers are spent, which makes it more valuable than its timing suggests, as the piece on the insect food web and the one on wild bees both describe.

Choose your thistle. Spear thistle is a biennial and stays put; pull or dig the ones you do not want before they seed and it behaves. Creeping thistle runs at the root and needs a firmer hand if you have a small plot, so give it a defined corner or keep it deadheaded.

Learn the caterpillar. Black-and-gold hooped caterpillars on ragwort are cinnabar larvae. Leave them be. Their appetite will often knock the ragwort back for you.

Handle with gloves and good sense. The alkaloids that trouble livestock are best kept off your skin, so wear gloves if you are pulling ragwort, and never add it to a pile animals can reach.

Resist the tidiness reflex. A mown, sprayed, weed-free margin looks cared for and does very little. The scruffy version is carrying most of the life.

The label and the ledger

There is a version of this story for anyone who runs an organisation, and it is worth telling plainly rather than prettily. "Injurious" is a label assigned on a single axis: agricultural yield. Judged on that one measure, these plants score badly, and so a whole apparatus of removal grew up around the label. Judged on a different axis, the one the label never looked at, the same plants turn out to be among the most valuable in the landscape.

The lesson is not the cosy one that everything dismissed as a weed is secretly a treasure. Some weeds really do cost you, and some underperformers really are just underperforming. The discipline is narrower and harder: to notice when a label has been inherited rather than tested, and to check it against the parts of the ledger it was never designed to measure.

The gentle point of all this

Pass a verge of ragwort and thistle in high summer, humming with more life than the border you planted on purpose, and you need not romanticise it. You can hold both things at once: that these plants can harm a horse in a hay net, and that they naturally feed more of Britain's insect life than the wildflowers we pay to sow. Leave the ragwort at the field's edge. Keep it out of the hay. Let the awkward, honest, disproportionately generous truth be enough.

References and further reading

• Balfour, N. J. & Ratnieks, F. L. W. (2022). The disproportionate value of 'weeds' to pollinators and biodiversity. Journal of Applied Ecology, 59, 1209–1218.

• University of Sussex, Laboratory of Apiculture and Social Insects (2022). Research demonstrates high value 'injurious weeds' can bring to pollinators and biodiversity. News release.

• Weeds Act 1959 and Ragwort Control Act 2003 (legislation.gov.uk).

• Defra (2004). Code of Practice on How to Prevent the Spread of Ragwort.

• Buglife. Ragwort: Noxious weed or precious wildflower? (information sheet).

• Butterfly Conservation and The Wildlife Trusts. Species profiles for the cinnabar moth (Tyria jacobaeae).

• Database of Pollinator Interactions (DoPI), dopi.org.uk.

• Database of Insects and their Food Plants (DBIF), Biological Records Centre.

• Merck Veterinary Manual. Pyrrolizidine alkaloidosis (ragwort poisoning).

• British Veterinary Association commentary on ragwort toxicity in horses and livestock.