# Odd leaf mottling across many orchids of various types



## drbeeraz (Oct 10, 2020)

I have been noticing that many of my orchids have been developing this "mottled" type of leaf changes. It seems to be involving an increasing number of orchids in my greenhouse of all kinds of different type. I have treated for fungal infection, there appear to be no mites or other insects. I water everytime with RO water with 1/4 strength MSO fertilizer although that has been only for the last month or so. Previously I was watering with Growmore fertilizer which lacked Mg and Ca so thought that might be the problem. It hasn't really changed anything. If anyone has any thoughts on the pictures below as to what the problem might be I would be extremely grateful....


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## cnycharles (Oct 11, 2020)

Not sure. But you may be on track thinking it’s a micronutrient. Has there been new growth since your change that would show improvement on the new growth?


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## Ray (Oct 11, 2020)

I’d bet on a magnesium deficiency.

The next couple of times you water, add a teaspoon of Epsom Salts per gallon.


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## Ozpaph (Oct 12, 2020)

some sort of chlorosis from nutrient deficiency.


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## podiver (Oct 13, 2020)

Are you growing under LED lighting? I had a similar problem and found that with the significantly increased growth, there was not enough nutrition and micronutrients to keep pace with the plant's growth. I agree with Ray that there could be a magnesium deficiency if this chlorosis is first noticed in the older leaves, as magnesium will translocate to the newer growth. After using Epson salts at Ray's recommended strength, check the newer growths for a return to your 'normal' color. Good luck..


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## Ray (Oct 14, 2020)

With some luck, the existing growths will green up, as well.

I had been applying 25 ppm N K-Lite (containing 3% Mg) at every watering when I grew in a greenhouse in PA, but upon moving to NC and putting my plants out on my deck, I got lazy and just used tap water, with only the occasional feeding. Little did I realize that our water has essentially NO magnesium, and a matter of months down the road, I saw similar chlorosis mottling.

At that point, I did a “recoup” treatment of a teaspoon Epsom Salts per gallon once a week for a month, and have gotten better about feeding more regularly since.

In a recent conversation with a PhD in horticulture, he mentioned that “orchids seem to be quite demanding of magnesium”, whatever that meant. I don’t know that the need is any greater than with other plants, especially considering the slow growers they are (relatively speaking).


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## drbeeraz (Oct 15, 2020)

Thanks to everyone for your input. I do not grow under lights, I grow in a greenhouse in AZ. I increase humidity with misters and control temperature with a water wall and a supplemental forced air swamp cooler. Have added Epsom salts as suggested. Will continue to do so. It definitely seems to have been affecting older growth as the new growth on things does not seem to have the same mottling. This is a fairly new greenhouse as I moved from an 8x16 to a 16x30 so the entire cultural experience is different and harder to control (temp, humidity, light etc...). The only other thing besides infection or micronutrient deficiency that I was considering is if the temperature of the water I am using to water is too cold in comparison to the greenhouse temperature. I store the RO water in a 15 gallon sprayer under the benches. I was wondering if it is colder still by mid morning compared with the air in the greenhouse and causing mesophyll cell collapse. Will update how the addition of the Mag helps.


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## drbeeraz (Oct 15, 2020)

One other thing, I use softened water to feed my RO system. The water softener system is loaded with potassium so there may be a slight amount of increased potassium in the feed to the RO, but I believe that the RO system would remove that. Should I have any concern with this set up as it pertains to potassium? Thanks.


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## Ozpaph (Oct 16, 2020)

Ray will know


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## Duck Slipper (Oct 17, 2020)

drbeeraz said:


> Thanks to everyone for your input. I do not grow under lights, I grow in a greenhouse in AZ. I increase humidity with misters and control temperature with a water wall and a supplemental forced air swamp cooler. Have added Epsom salts as suggested. Will continue to do so. It definitely seems to have been affecting older growth as the new growth on things does not seem to have the same mottling. This is a fairly new greenhouse as I moved from an 8x16 to a 16x30 so the entire cultural experience is different and harder to control (temp, humidity, light etc...). The only other thing besides infection or micronutrient deficiency that I was considering is if the temperature of the water I am using to water is too cold in comparison to the greenhouse temperature. I store the RO water in a 15 gallon sprayer under the benches. I was wondering if it is colder still by mid morning compared with the air in the greenhouse and causing mesophyll cell collapse. Will update how the addition of the Mag helps.


The cold water issue you can rule out with the use of a aquarium heater. You can purchase them in many different wattages depending on how much water you are wanting to keep warm.


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## Ray (Oct 17, 2020)

Softened water will usually be easier to purify with reverse osmosis than is "raw" water. Potassium is a relatively large ion, so should be easily rejected.

My well water in PA had a pH of 4.3-4.7 and for years we injected potassium carbonate solution to neutralize it - added, not substituted. My RO water in the greenhouse was still single digits.


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## SouthPark (Oct 20, 2020)

drbeeraz said:


> I have been noticing that many of my orchids have been developing this "mottled" type of leaf changes.



How long roughly have those plants been growing there for?

Maybe your new fertiliser that has the mag-cal in it has neutralised the effect. It has only been 1 month, so give some more time. Is the light intensity pretty high in the growing area? Also consider temperature and air-movement.

It probably isn't cell collapse ----- otherwise the leaves would have sunken portions, and dark or brown patches after that.


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