Monday 10 September 2018

Should we worry about poisonous plants?

Irritating plants

Oleander is one nature's most poisonous plants
My opening comments are about this troublesome weed
Yet again I rub my eye in Pavlovian response. My itch becomes more intense and my eyes start to water. I have been weeding again and it’s that damned petty spurge. I prepare myself for a couple of hours discomfort. I am lucky of course and it could be very much worse. 
Last night Cathi thought I had an eye infection and I had to explain

Do not rub your eyes after weeding this plant
This nasty pretty little weed is Euphorbia peplus and has toxic white milky sap. So do the rest of this huge family Euphorbiacea which includes numerous loved garden and indoor plants - not least poinsettia. Handle all of them with care and beware getting their sticky white milk on your skin.

Petty spurge is of delicate nature and pervades almost un-noticed amongst and within your plant clumps. You are more likely to have a problem if you are rather good at weed control where it has less competition and you are at first blind to its presence. It is an extremely common weed and few gardens avoid it.
It comes from seed and is easily controlled if you remember to do so. One just forgets.

Just pull it out at the roots with a gentle pull. Take care not to snap the stem and get toxic sap on your hand. Leave it to desiccate and die or if you are just too tidy take it to  compost. You ought to wear gloves but I constantly lose them somewhere round the garden. None of mine match

Petty spurge has had a field day in this Summer's drought
Very shallow hoeing is ideal and is the safest method. Unfortunately most modern Dutch hoes are next to useless and difficult to skim with. My own onion hoe would be ideal but I have lost it.
I do not find spraying works very well. The weed  starts so very small and the glyphosate tends to run off and I suspect it does not translocate very well.

Even the nice euphorbias have toxic sap
Hot chillis
I am told if you have been slicing hot chilli the sap on your hand can cause very similar stinging sensations in sensitive places.

A different kind of irritant

Rue, Ruta graveolons
Another plant to which I have fallen victim is rue, Ruta graveolons. This so called herb is a nondescript  dwarf evergreen glaucous shrub I have encountered in past client’s gardens when I have pruned. This has a photosensitive sap that causes phytophotodermatitis. You might get away with exposure to its sap on intact skin but any cut or graze - common when pruning, especially if you catch yourself on a cut ruta stump, is real nasty. You will recover but it’s not nice at the time

The affect of sap of the herb rue is not very nice
Many plant sensitivities are specific to just a few people. I once had a student who after pruning common ivy came out in a dreadful rash. I myself hate handling Christmas trees which give my hands a sore feeling. The house plant Primula obconica is rather notorious for causing a rash (and breeders have bred a safe variety called ‘Touch me’). 
Less well known is that chrysanthemum sap can irritate, so can the small tree rhus

Rhus sucker
Really poisonous plants

Deadly wolfsbane can be extracted from Monkshood, aconitum
It’s not my intention to prepare a compendium of poisonous plants but merely to make a few observations. 
There are hundreds of garden plants that are poisonous. Some fatally so. Should we be worried that many much loved plants have the capacity to kill you?
I do not think so but be very careful. Never eat any plant part unless you know it to be safe. 
I have at least a dozen really toxic plants in my garden including an oleander that I struggle to grow! My only concession to their nature is to thoroughly wash my hands after any close contact such as cutting or pulling. 
Last month in a French garden I very carefully pulled out a very strong growing deadly nightshade with my bare hands and I am still here. (I don’t mean in France).

Weeds such as ragwort are deadly poisonous to grazing animals

If you read a list of potentially poisonous plants you might give up and grow nothing at all. I am firmly against any suggestion that poisonous plants be compulsory labelled. Such is human nature that most of the plants in the garden centre would be so marked. Just think of a few examples

Lily of the valley. Now that’s really poisonous

Arums.  Although there are several cases each year of hospitalisation when the red berries have been eaten it is a long time since there were any recorded deaths.

Asparagus. Its berries are poisonous albeit mildly. 

Tomato. The only edible and none poisonous part of the plant is the tomato fruit. (Fortunately there are no dangers growing them)

Rhubarb. Fears of oxalic acid in the leaves are grossly overrated although the leaves contain another chemical which is also toxic

My poisonous pokeweed is regularly asked about on my open days

Parsley. My favourite herb that I safely devour in some quantity in sauces or in sandwiches contains five times the concentration of oxalic acid as rhubarb leaves

Aconite. I am not about to prepare wolfbane from this plant's deadly content

Potato.  Young tubers exposed to sunlight produce deadly solanin  indicated by the presence of harmless green chlorophyll 

Even my beloved dicentra are toxic

Narcissus. There have been cases of thinking they were onions with nearly fatal consequences

Laburnum. A client gave her pet rabbits a treat placing them in a bottomless cage on the lawn under a laburnum that was casting its seeds. Oh dear.

Digitalin is extracted from poisonous foxgloves to treat heart disorders
This is an excellent reference list of poisonous plants in wikipedia which will either reassure or persuade you gardening is not for you.

There is a garden of poisonous plants in North Yorkshire. I understand you can only go round with a chaperone. That sounds a gimmick to me.

And a final thought, most vegetables contain tiny levels of toxins and there is very strong evidence that this is the reason why they are good for you

I write about the 'nearly myth' of poisonous oxalic acid in rhubarb leaves here


  1. You have done a good job of covering all the angles on this.
    I write this with a tingling hand - The culprit the humble stinging nettle. Makes great soup though!

    1. Yesterday I put my hand through the undergrowth of the tomatoes to pull out a bundle of weeds at the back ... and guess what!

  2. Years ago a neighbour was frightened when he thought he was suddenly going blind. He went to the hospital and was told that something had irritated his eyes. He had been working in the garden and asked me to look and see if I could tell him which plant could have caused his problem. I soon identified euphorbia in the part of the garden he had been working on, He removed it.

    I think one plant that many people don’t realise can cause serious skin problems is the parsnip. The sap when it gets onto skin especially in sunlight can cause burns and cause the skin to become photosensitive for a few years afterwards.

    I find my hands itch when I pick tomatoes after brushing against the leaves and stems. When hands are washed afterwards the soap suds turn yellow.

    I can testify to the effect chillies have on hands although I have no experience of what I think you are alluding to.

  3. Thanks Sue for this valuable contribution. I wonder if other readers have any experiences to report
    The yellow pigment from tomato leaves rings a bell - i shall examine my hands very carefully next time I work with tomatoes. I seem to remember professional pickers getting stained hands and the characteristic smell
    As to your final comment I would add "neither have I"

  4. Another interesting article, with food for thought, not poisonous of course...I have visited the garden you refer to at Alnwick Castle, and it is quite interesting going through it with different guides. Of course as a gardener who started learning as soon as I could toddle after my father, and having an inquiring mind, I apply knowledge and experience. I have reactions to some plants, and therefore garden with appropriate PPE when I work on particular plants. But the important thing is I still grow and love them!

    1. Thanks for identifying the garden as Alnwick Castle. I really ought to go and see it - its just that I cannot imagine I would like a place that has spent so much money...
      Although on a different note my first garden foreman at Hartlepool Parks Dept and who taught me so much had been a gardener at Alnwick Castle -seventy years ago

  5. Last week I discovered a hemlock plant growing up in a pot of hostas. I was so alarmed I couldn't do any gardening for a day or two! Do you know the safest way of disposing of it? Thanks

    1. There is no need to panic Amanda. I would just pull it out and burn it or compost it. Make sure any seeds are destroyed. Just gently handling it is quite safe. As you are worried wear gloves.
      There are actually many umbelliferous plants that could be confused with hemlock. I might be able to identify it for you if you sent me a picture at

  6. Thank you Roger!

    With the fern-like leaves sprouting from a base, funny smell and purple splotches I'm pretty sure it's a nasty one. Fortunately no flowers as yet. I think it flowers the following year?

    1. Yes it is a biennial Amanda. I expect you have checked it out on google images but of course many of their pictures are of the flowers.

  7. Good to get this knowledge out there. Thanks


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