# Magesium and light



## Stone (Dec 3, 2013)

Does anyone know if increased light levels increase the incidence/possibility/symptom of Mg deficiency?
Reason: after a very cool and sunless spring, we are now getting intense sunlight regularly and I've noticed yellow mottling on older leaves (not so much on Paphs..shaded) on just about everything and suddlenly! Can't seem to post pics at the moment but it looks like this:
http://www.orchidboard.com/community/cattleya-alliance/21125-catts-leaves-whats-wrong.html
and this:
http://www.cloudsorchids.com/doctor/pdefic.jpg


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## gonewild (Dec 3, 2013)

Are the light levels beyond the levels the species normally like?
In other words are the plants getting more light than you would normally allow?


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## Stone (Dec 4, 2013)

gonewild said:


> Are the light levels beyond the levels the species normally like?
> In other words are the plants getting more light than you would normally allow?



No. But I do remember something similar last year but not as bad. Its affecting everything from Catts to Oncidiums to Coelogynes to Masdevallias (which actually are well shaded come to think of it)
I've sprayed a heavy dose of MgSo4 with a wetting agent on all plants and intend to repeat every 10 days or so. We'll see if it helps but they might be slow to respond if they even do.


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## Ozpaph (Dec 4, 2013)

K-Lite......................................


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## gonewild (Dec 4, 2013)

I know you have previously said what nutrients you are using but please define it again here in this thread so it is associated with this problem.


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## gonewild (Dec 4, 2013)

It may be that the leaves have just stopped producing chlorophyll because of the increased light rather than a mineral deficiency.


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## naoki (Dec 4, 2013)

Mike, I didn't know about this (and thanks for bringing this up), but it sounds like that in other plants, Mg deficiency + high light intensity causes chlorosis. It kind of makes sense if the chlorophyll renewal is more rapid (i.e. shorter longevity of chlorophyl) under higher light intensity.

I read a bit more. Hmmm, actually the reason for symptoms of Mg deficiency in high light is a bit more complicated. p.284, the top paragraph:
http://books.google.com/books?id=1F...eficiency light intensity chlorophyll&f=false


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## Trithor (Dec 4, 2013)

I always get concerned when a problem is treated with a heavy dose of anything. I think we tend to look at plants in animal terms. Plants do most things slowly (except die, that they seem to do quickly), and as such they do not respond quickly to a change or new input, which tempts the 'plant doctor' to repeat or even increase the treatment. 
Any advice that I could give is that 'slowly slowly catchee monkey' and always in moderation. Don't rush, think it through and give any change you make a chance to have an effect before you make another change, or else before you know it you will have made so many changes that you don't know what is working and what is making things worse.


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## Rick (Dec 4, 2013)

Problem is symptoms of Mg deficiency are also the same as symptoms of excess K, or excess Ca.

Orchids thrive on a lot less than we typically give them, so over the last 2+ years every time I see what I think is a deficiency, I've tried to look at it from the reverse standpoint as what is in excess.

That was the main premiss for low K in the first place.

What I've also been seeing lately (that seems to be working) is that when K is reduced, photosynthetic rates go up, which does increase need for Mg and P (probably also sulfate and iron).

So excess limestone in potting mix ties up P and Fe, and may cause a Ca/Mg imbalance. So I did make a solution of MgOH neutralized with phosphoric acid and added some MgSO4 and tiny amount FeSO4. And after cutting K lite way back to 5 ppm N added a few ppm of Mg back in from this stuff.

There is a comercial DynaGrow bloom boost formula that is very similar to my Mg SO4/PO4 formula, but has a dash of potassium nitrate in it. 

But you might try alternating very low doses of your present fert with very low doses of a similar bloom boost (with cal/mag) fert.


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## Stone (Dec 4, 2013)

Trithor said:


> I always get concerned when a problem is treated with a heavy dose of anything. I think we tend to look at plants in animal terms. Plants do most things slowly (except die, that they seem to do quickly), and as such they do not respond quickly to a change or new input, which tempts the 'plant doctor' to repeat or even increase the treatment.
> Any advice that I could give is that 'slowly slowly catchee monkey' and always in moderation. Don't rush, think it through and give any change you make a chance to have an effect before you make another change, or else before you know it you will have made so many changes that you don't know what is working and what is making things worse.



Generally I agree with you that if you need to ''heavy dose'' anything there is something fundamentally wrong. And yes it will be Mg only and no other treatment until I see any change.
I'm guessing Mg deficiency but in no way am I certain. I read up on correcting Mg deficiency through foliar spraying. Recommendations were for 20gms per Lt MgSo4 with several sprays probably needed. Its really a (hopefully quick) test as to whether it makes a difference. If it does, then I'll have to take more permantent action. such as supplying more Mg to the medium and/or less K and/or Ca. or more shade. However the light they are getting should really not be exessive. 
If it makes things worse, well that might give me another clue, and if nothing changes I'm back to square one.
Most of the plants (but not all) affected recieved osmocote with high Mg (for citrus) + a similar amount of rock gypsum to supply the Ca. It could be possible they are getting too much Ca? NPK of the fertilizer is 18.7-2-6.5 + 2.5Mg. TE's are pretty standard. Water pH is around 6.5 with little in the way of Ca and Mg.


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## Stone (Dec 4, 2013)

naoki said:


> Mike, I didn't know about this (and thanks for bringing this up), but it sounds like that in other plants, Mg deficiency + high light intensity causes chlorosis. It kind of makes sense if the chlorophyll renewal is more rapid (i.e. shorter longevity of chlorophyl) under higher light intensity.
> 
> I read a bit more. Hmmm, actually the reason for symptoms of Mg deficiency in high light is a bit more complicated. p.284, the top paragraph:
> http://books.google.com/books?id=1F...eficiency light intensity chlorophyll&f=false



Thanks naoki, I thought the low Mg symptoms coming with the increasing light HAD to be relevent somehow!


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