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Rhododendron nectar toxic to honeybees - who knew?

Surprising things can be learned in church.  This morning, Pastor Paul illustrated his sermon by likening sin to Rhododendron ponticum, in that it is invasive, pervasive, destructive and difficult to contain and control.  All of which I knew. He then went on to say - which I'd never heard before - that its nectar and/or pollen are toxic, sometimes lethally so, to some species of bee, including honeybees.

This struck me, as a biologist by training, as a touch improbable.  Flowering plants and pollinating insects are interdependent, so a plant that poisons its pollinators would seem to be cutting off its nose to spite its face.  I decided after the service, I must ask him his source for this information.  Before I had time to do that, Timothy, a keen gardener, leant over to me saying, "Does this mean I should rip out all my rhododendrons?"  

We consulted Nicholas, who is not only a very knowledgeable and experienced gardener, but also a beekeeper and retired biology teacher.  He'd heard the same thing from at least two reputable sources.  So I came home and googled it.

The plot thickens!   It seems that bees that forage among rhododendrons produce "mad honey", which European armies have have been using as a weapon of war for centuries.  You leave it in the path of enemy troops, they eat it, and within a few hours are nauseous and disorientated.  It would only work once, wouldn't it?

It seems that only certain species of bees are affected.  Those that are are co-indigenous with R. ponticum know to leave it alone.  Natural selection would see to that, but has not yet had long enough to do so in places where R. ponticum has been introduced.  The plant gets away with it because there are enough other kinds of insects to pollinate it. 

Also, not all species of rhododendron are guilty.  One of the websites I looked at said there are roughly 1,000 species and innumerable hybrids, so that it can be difficult to identify any one plant with certainty.  The only likely culprit in my garden is known by several combinations of "Rhododendron", "Azalea", "ponticum" and "luteum".  The growers, and even the RHS, can't seem to decide what to call it.  It's a favourite of mine, and I'd set my heart on growing it "if ever I have a garden", and now I have, I have planted three of them and was intending to plant a fourth.  So I would be loath to get rid of them.

Aside from that, the rest of the sermon, on Joshua chapter 7,  was most edifying, and if you care to hear it, search "Queen's Road Church, Llandudno."


  • pansyfacepansyface PEAK DISTRICT DerbyshirePosts: 21,196
    Yes, I had heard about that years ago from my dad who was a keen beekeeper.

    This article is interesting.

    The rhododendrons appear to be choosing the most beneficial pollinators by weeding out the least efficient ones. And as a byproduct of this natural selection, the relentless spread of rhododendron ponticum would seem to be guaranteed.

    Rhododendrons use chemicals as deterrents, whereas coffee plants use caffeine as a reward, it seems.

    Apophthegm -  a big word for a small thought.
  • ObelixxObelixx Vendée, Western FrancePosts: 28,555
    Well, I think I prefer the reward system!   

    Good job there's no rhodo ponticum in my plot but what about other rhodos?  I have 3 so far.  Should I stop now??  And is it the same for azaleas?
    "We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
  • How interesting ! Thank you for this very useful info. I don't think I can look at my Rhodedendron bush in the same way now though.
  • glasgowdanglasgowdan Posts: 632
    These toxic Rhodies aren't kiling bees... the bees just avoid them.  Don't go digging up your plants!
  • LynLyn DevonPosts: 21,137
    I was  just going to say the same Dan, I’ve never seen a bee on mine.  Or azaleas,  don’t know about camellias.
    Gardening on the wild, windy west side of Dartmoor. 

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