The Poison Garden is an oddly captivating blog on many weird and wonderful poisonous plants. Since spending some time there, I’ve realised our dairy yard is ringed by hemlock – the deadly plant Socrates drank as his death sentence.

I was thrilled when The Poison Garden’s author, John Robertson, agreed to write this post for the Milk Maid Marian.

The only type of question I dread about poisonous plants begins ‘Should I remove…?’ You can’t say that it is fine to leave the plant(s) alone because that’s sure to mean the questioner’s dog ends up dead within a few weeks but it has to be remembered that, in the majority of cases, the plant concerned has been growing in gardens, parks or open country for hundreds of years and rarely, if ever, caused a problem.

But what about farmland? Loss of a beloved pet may be heart-rending but loss of a herd of cattle because of some unrecognised risk could bring financial ruin on top of the emotional upset.

Instances of poisoning due to plants are, thankfully, rare but they do happen and they do happen more with farm animals than anything else. Just this week, I saw this (pdf) report of an incident in the Republic of Ireland where a herd of cattle fell ill, and some died, three weeks after being turned out to a new pasture. Thorough investigations proved that the cause was ensiled ragwort, Jacobaea vulgaris, in the feed the animals had been given prior to being let out but it would have been natural to assume that there must have been something in that new pasture since the cattle showed no signs of illness prior to their release.

The buttery yellow flowers of ragwort

I mentioned this case to Esther Hegt who runs the website ‘Ragwort, myths and facts’ and she replied by telling me about a case some years ago in the Netherlands where 250 cattle suffered ragwort poisoning after being fed hay that was badly contaminated with ragwort.

So what should a farmer do? Well, as I said at the start these poisonous plants have been around for a very long time and only rarely do harm. That may be because the taste deters consumption in normal times or it may be that the animal has evolved not to be attracted to a particular plant. Especially in this age where bio-diversity is king and farmers are expected to protect the environment and feed people, it is not possible to tour every inch of land and remove anything that just might cause problems.

What is important is to be on the lookout for the unusual. The recent poisoning of a Chinese chef in Canberra occurred when an exceptional spell of weather produced fruiting bodies on the Amanita phalloides, death cap mushroom, at the ‘wrong’ time of year and past incidents involving cattle often result from something different happening. A very dry spell early in the spring leading to the ground shrinking and exposing the roots of Oenanthe crocata, hemlock water dropwort, resulted in deaths in cattle though the same pasture had been used for many years with no trouble.

The pretty yet deadly hemlock rings Milk Maid Marian's dairy

Of course, the other thing that can lead to poisoning incidents is lack of knowledge. A number of incidents have occurred when people didn’t realise that Taxus baccata, yew, or Nerium oleander, oleander, were toxic and thought they were being helpful by feeding clippings from these plants to farm, or zoo, animals.

Something different is mostly the cause of one of these rare incidents so it is worth saying that there is something different about modern farming where, perhaps, not enough consideration is being given to possible plant poisonings.

Whether as a commercial venture or in order to be more transparent about farming practices, more farmers are inviting the public onto their farms. It is almost certainly worth spending a couple of minutes making sure those visitors understand why they shouldn’t feed treats, of any sort, to any of the animals they will meet during their visit.