[Betterhaff]

Think about the physics and the scenario. If you lay a magnifying glass on a leaf in sunlight, what happens? Nothing except you get a little more intense glow in the field of the glass. Now if you lift the magnifier a few inches and find the proper angle, the light is focused and/or concentrated enough to cause burning, maybe even combustion. Does this happen with raindrops? I suppose it could if they were somehow suspended above enough and the proper angle achieved but that scenario is probably a very rare event.

[Budley Doright]

Originally Posted by Betterhaff

Think about the physics and the scenario. If you lay a magnifying glass on a leaf in sunlight, what happens? Nothing except you get a little more intense glow in the field of the glass. Now if you lift the magnifier a few inches and find the proper angle, the light is focused and/or concentrated enough to cause burning, maybe even combustion. Does this happen with raindrops? I suppose it could if they were somehow suspended above enough and the proper angle achieved but that scenario is probably a very rare event.

Yup..... this is called the focal distance... its impossible for a drop of pure water to cause a burn....

However.... and likely where the tale comes from....if you put a drop of water with fertilizer in it.....that can cause a burn.... but not in the way you might think....

as the drop dries up the fertilizer becomes less dilute...less water and eventually the drop can burn the plant......

fertilizer burn....not magnification burn.....

[brown_thumb]

Originally Posted by Budley Doright

Yup..... this is called the focal distance... its impossible for a drop of pure water to cause a burn....

However.... and likely where the tale comes from....if you put a drop of water with fertilizer in it.....that can cause a burn.... but not in the way you might think....

as the drop dries up the fertilizer becomes less dilute...less water and eventually the drop can burn the plant......

fertilizer burn....not magnification burn.....

I was told by a retailer that I burned my plants after foliar treatment with neem oil. He said it's a photo-induced chemical burn, not a focused light burn. My assumption is, situations similar to this is where this 'wife's tale' began. And, like many other wives' tails, it's repeated over and over again until it becomes 'known fact'. It's NOT a fact but rather a misrepresentation of a DIFFERENT truth. It's not a focused water-lens burn... it's the stuff IN the water reacting with light, heat and plant leaves.

[Budley Doright]

Originally Posted by brown_thumb

I was told by a retailer that I burned my plants after foliar treatment with neem oil. He said it's a photo-induced chemical burn, not a focused light burn. My assumption is, situations similar to this is where this 'wife's tale' began. And, like many other wives' tails, it's repeated over and over again until it becomes 'known fact'. It's NOT a fact but rather a misrepresentation of a DIFFERENT truth. It's not a focused water-lens burn... it's the stuff IN the water reacting with light, heat and plant leaves.

Kinda funny story.... There is a sick plants thread done by someone by the name of My Name Stitch..... she had a book published and all....

well when we were both on Overgrow we had a big argument on this topic..... it took me a few shots before I could convince her......

Actually I helped her with some of the pictures she used in both her book and the thread....however some of the pictures she used were because they looked like a certain condition ...... not that the deficiency actually caused the condition....

I tell folks you are better off going to Canna Usa and using their sick plant guide than hers....

[Budley Doright]

Hairy leaves
But what about the hairy plants? The leaves have hairs that are 'hydrophobic' or 'water-hating'. Under the right circumstances, these hairs could catch a water droplet and keep it suspended at the right distance above the leaf, to allow the focus point of the sunlight to land on the surface of the leaf. Because the water was not in contact with the leaf, there was no cooling effect. And the hairs, being water-hating, would repel the water, and so keep it spherical — the best shape to focus the sunlight.

But the hairs hate water, and the merest breath of wind would shake the droplets off. The smaller droplets were better at focusing the heat — but being smaller, they would also evaporate very quickly.

Even so, the scientists did sometimes see scorch marks produced by water droplets on hairy leaves.

How did this 'don't-water-plants-at-midday' story arise? Who knows?

But you'd think that after half-a-billion years of bio-evolution, plants (which have adapted to every conceivable ecological niche) would have learnt to deal with a little rain ...

[brown_thumb]

Originally Posted by Budley Doright

Hairy leaves
But what about the hairy plants? The leaves have hairs that are 'hydrophobic' or 'water-hating'. Under the right circumstances, these hairs could catch a water droplet and keep it suspended at the right distance above the leaf, to allow the focus point of the sunlight to land on the surface of the leaf. Because the water was not in contact with the leaf, there was no cooling effect. And the hairs, being water-hating, would repel the water, and so keep it spherical — the best shape to focus the sunlight.

But the hairs hate water, and the merest breath of wind would shake the droplets off. The smaller droplets were better at focusing the heat — but being smaller, they would also evaporate very quickly.

Even so, the scientists did sometimes see scorch marks produced by water droplets on hairy leaves.

How did this 'don't-water-plants-at-midday' story arise? Who knows?

But you'd think that after half-a-billion years of bio-evolution, plants (which have adapted to every conceivable ecological niche) would have learnt to deal with a little rain ...

My point precisely!!

[Leaf Eater]

Originally Posted by Gry

https://www.scientificamerican.com/p...burn-10-01-12/

hey Gry that sounds like a yes to me and that was very good thanks cant rep you sorry

[Budley Doright]

Originally Posted by Leaf Eater

hey Gry that sounds like a yes to me and that was very good thanks cant rep you sorry

Well not really..... cannabis leaves would be among those that dont burn.....

[Phaeton]

Originally Posted by Gry

https://www.scientificamerican.com/p...burn-10-01-12/

While I still have subscription to Scientific American (since 1987) the quality of the magazine dropped dramatically in the 2000's.
This is an example of their deterioration.

No terrestrial (land) plants were shown to have ever been burned by sun on water.
One marine plant held spherical water drops in the air above the leaf surface and damage was found.
One plant. Not a land plant, no land plants could hold spherical water drops at the correct distance, not one.

As an analogy, water is poison and will kill if consumed in large quantity. Not a realistic problem, kinda on the same shelf as droplet burns on leaves.
It is NOT going to happen in the real world.

[Gry]

Threw my tv out 20 years ago over what they did to nova.
Integrity is the good stuff.