Monday, 13 August 2012

Garden myths debunked: water scorch by magnification


‘Water droplets on leaves act as a lens in sunshine and scorch the leaves’

Harry next door fell about laughing at this. He has spent 25 years in Africa and has seen tropical sunshine follow rain. He has never seen foliage sun scorched afterwards. The physics and maths of it are quite impossible and the theory goes firmly in the bin.

Thoroughly wetting 
my tomatoes in full sunshine. 
The plants love it and the
 force of the spray aids pollination.
Behind many garden myths there IS some truth.

It will be wrong to wet my tomato leaves in a few weeks time! As the days shorten, dampness and grey mould disease threatens.

Some plants, such as African violets, are notoriously liable to ‘water scorch’ when the foliage is wet. This is often worse in damp places where there is no direct sunshine.

Pesticide sprays in full sunshine become concentrated by evaporation and can also sometimes scorch.

Completely dry pot plants desiccate and die when left in strong sunshine for too long.

Postscript

Years ago, a world famous alpine gardener spoke to 100 students at Askham Bryan College. He started with, ‘Do you know, water droplets act as a lens…’ A very timid young lecturer slid down in his seat. My students, bless them, never said a word! 

No need here to wet the foliage, but there is no harm if you do.


10 comments:

  1. Despite this being thoroughly debunked by research done at the University of Budapest, several very well-known gardening organisations are still happily perpetuating the myth!

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  2. Thanks Laurie for your immediate support. I have a pretty long list of myths for future posts.

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    1. It's amazing how many people just refuse to accept the evidence though. When the Hungarian research was published, the tabloids ran with it in their gardening columns, and got inundated with comments from the disbelieving public! Or perhaps that should be 'disbelieving tabloid public'!

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    2. I wonder what folk are doing when they water that preserves this illusion. I have known new gardeners with no idea how much water to give their plants. I suspect in many cases there might be desiccation due to just lack of sufficient water when the plant is in strong sunshine.

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    3. You may be right Roger. However, I suspect that inherited prejudice is another likely candidate. There again, when a new gardener sees the likes of Kew promulgating the myth, who are we to blame them for their ignorance!

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    4. I would be really interested in bloggers experience of water scorch phenomenon.

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    5. I don't think you'll have any takers on that one Roger - the phenomenon doesn't exist!

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    6. Not the magnifying lens rubbish I know. But there are scorching problems that do occur. Scorched wet leaves on saintpaulias are not thought to be a disease but it does happen quite frequently. I am not sure where to go for a botanical explanation. I did have my own theory why the lens myth arose but as my botanical friends say that it's wrong I have refrained from repeating it!

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