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Bee-friendly Himalayan balsam

Three of the colours seen in Impatiens glandulifera, Himalayan balsam, in Northamptonshire. Images ©GardenPhotos.com
Himalayan balsam, Impatiens glandulifera, is a common plant of British riversides, pond margins and other wet places and is always said to be too invasive for us to be allowed to grow. It looks as if it’s smothering everything else where it grows, so it’s banned. It can be a lovely plant, so not being allowed to grow it is unfortunate.

On my recent short visit back to England I saw it along the River Nene in Northamptonshire (along with the American native Imaptiens capensis), by the Wey Navigation Canal and River Wey in Surrey and in other waterside places. Some stands of it looked dense and were well over 6ft/2m high.

Impatiens glandulifera, Himalayan balsam, growing by the River Wey in Surrey. Image ©GardenPhotos.comBut the most striking feature was the colours. The flowers varied from cherry red through various purplish and pink shades, including some pretty bicoloured forms, to almost white. Years ago I used to grow a pure white form called ‘Candida’ (with none of the anthocyanins that bring the red and pink colouring); it’s very pretty, but those pale flowered plants I came across this year all had a faint blush of pink.

Also known as policeman’s helmet from the similarity of the flower shape (though not the colour!) to the helmets worn by London policemen, it’s listed as a noxious weed in three US states though it’s not yet found in most country.

However – is it really that bad? Needless to say Ken Thompson gives us the low down in his latest book, Where Do Camels Belong? The Story and Science of Invasive Species. Himalayan balsam in Britain, like purple loosestrife (Lythrum salicaria) in North America, turns out to be an example of a plant that looks as if it’s smothering everything to extinction while the basic science tells a different story.

Dr. Thompson reports that a large scientific study that compared areas that had been invaded with similar habitats that had not concluded that “it (Himalayan balsam) does not represent threat to the plant diversity of invaded areas”. But although one visual assessment turns out to be misjudged, another turns out to be valid. The late flowering of Impatiens glandulifera provides valuable food for bees when few other plants in its favoured damp habitats are flowering. So it’s actually quite useful as well as attractive – so it’s shame that we’re not supposed to grow it.

Comments

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T. P. O'Rourke

There you go again... Praising plants we all know smother our cherished natives to death. You'll be telling us all to plant Japanese knotweed next!

Graham Rice

Fair and balanced, that's us, fair and balanced. And being fair means saying "never plant Japanese knotweed" and being balanced means saying "not even the variegated form". OK?!

But the fact is, TP, that the science shows that Himalayan balsam is not as bad as it's thought to be be. Just ask if you'd like the references to the scientific papers that set this out.

Mary Bennett

I've just been reading in the RHS magazine The Garden about a rust disease from India being introduced to attack Himalayan balsam but which, the article says, "will not eradicate the balsam". But the article says that the garden annual Impatiens balsamina and its varieties will be attacked. So it won't kill what its supposed to kill, but will kill a garden annual. Seems daft to me.

Graham Rice

Yes, I was just reading that too (my copy of The Garden has just arrived here in the US). Frankly, I'm not sure that we should worry too much about Impatiens balsamina which is hardly a top rank annual - almost no one grows it, these days, I can understand why, and few seed companies list it now.

I'd be more worried about all the species which are now being used to develop new patio plants and replacements for the cvs of I. walleriana which are being laid low by downy mildew.

There must be approaching a thousand Impatiens species and many of the showier ones are being investigated.

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