17 hours ago
I have mistletoe in my garden. Will it kill the host tree?
I have mistletoe in a tree in my garden. I was told to keep it as it's so unusual, but I'm afraid it might kill the host tree. Can you advise me?
S Doyle, Co Dublin
Relatively rare in Ireland, mistletoe (Viscum album, or 'drualas' as it's known as Gaeilge) is a hemiparasitic, non-native, shrubby evergreen species that depends on a host plant – typically a large, established, deciduous tree – to survive.
In the National Botanic Gardens in Glasnevin, where it was possibly deliberately introduced by the then curator of the gardens, Dr David Moore, in the Victorian era, this wildlife-friendly plant can be found growing on apple trees, birch, maples, robinias, davidias, limes, crataegus, sorbus and poplars. Its seed is typically spread by birds, which is why mistletoe is also increasingly found growing in private gardens close to the National Botanic Gardens. But despite its undoubted charm and ancient history of use (Virgil mentions it in the Aeneid), you're right to be somewhat concerned about the potential damage it might cause.
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Although it's relatively slow-growing, a large, well-established colony of mistletoe can stress the host plant, on which it is dependent as a source of water. This is particularly true during periods of drought, when the host tree is already under pressure and fighting to reduce water loss through transpiration and evaporation. As a result it's not unusual to see the latter showing signs of wilting during a prolonged dry spell. Mistletoe can also cause distortion and swelling of branches, gradually making host trees unstable. For this reason colonies in the National Botanic Gardens are very carefully managed and any potential damage is minimised by them being systematically harvested every couple of years to reduce their weight and spread.
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Unless you're prepared to similarly manage its growth, regrettably the safest choice is to cut the mistletoe out of your host tree. But removing it from your garden may be tricky, especially if it has established itself high up in branches where it's difficult to reach. There is, of course, the chance that it might re-establish itself, so you'll also need to keep a watchful eye out in the years to come.
