Purple leaves: Cold damage, Insect stress, too much light, magnesium or phosphorous

[Ray]

Let me open this with a big “thank you” for leading this discussion!

Originally Posted by Shadeflower

I know I'm not the only one who would love to understand nutrients better but it is challenging. I feel I am 1/20th there lol.

I’ve been studying orchid nutrition a great deal, and feel I fully understand a lot less that 1/20th! Every time I think I grasp an aspect, something turns up to tilt it on its head.

Based upon my reading, I think your assessment that P & K are both bloom and root growth stimulants is questionable. As I don’t know how rigidly you controlled things, it may very well be that the reduction in applied nitrogen that accompanied the increased P & K allowed the plant to put it’s resources into other-than-shoot growth.

I know that plant tissue analysis really tells you more about what the plant has been getting, and not what it needs. However, if you consider that a plant in the wild - especially a niche plant like an orchid - must be having its needs met (or it would be dead), analysis of wild-collected plants must give us results that are, at least, “in the ballpark “.

Those dry tissue analyses I have seen show them to be about 90% C, O, H, & N, with the N being anywhere from 1.5 to 3% of the mass. P, K, S, Ca, & Mg total about 9% of the mass, with each element being a fraction of the nitrogen content. Everything else makes up that last 1%.

I recently read a paper that showed freshly-matured cymbidium leaves contained N, P, and K in a 10-1-10 ratio, then learned they had been fed a fertilizer that had an elemental ratio almost identical to that.

[Shadeflower]

We can discuss about it and discuss about it but I will just add my observations.

adding too much P, causes a K deficiency instead so one has to be careful not to add too much or even better add P and K together.

I feel this is getting a bit too technical, I don't want to give any bad advice since I know how easy it is to give too much of something and cause worse results. So this is in the advanced discussion section for a reason.
I can also only add a few observations.

I showed this phal corningiana at the beginning of the thread and it's been a fusspot all year, now finally I think I have found what it was missing.
I had already added trace elements, that didn't do much, phosphorous alone didn't do much.

After finally managing to get some iron supplements and PK at the same time things have for the first time had an effect on this one.

The others I am still observing for now

one month ago:



After getting increased Iron and PK for 2 weeks:



Notice how the leaf wrinkling (leaf curvyness) has dissapeared! This was a symptom that I had been observing but didn't know what to do about

[Dusty Ol' Man]

Just out of curiosity what was your source of iron?

[Shadeflower]

curvy leaves anyone? It's a symptom that might not seem like much of a symptom but I think curvy leaves are no more.
This one has only received increased Phosphorous. I hadn't even noticed how badly squashed this leaf was till I adjusted my feed and then it grew a bit straighter.



I don't know how much effect the iron has had. I've only just started using it, more of a just in case.



I know I wouldn't believe these symptoms could possibly be related to phosphorus and who knows if they really are, I think so, but the main symptom is purpling on leaf undersides I believe. But it would be great if someone else had also noticed similar symptoms previously, and if anything improved it.

[Ray]

I just took a look at Marschner, who literally wrote the book on plant nutrition.

He states that “the phosphorus requirement for optimal growth is in the range of 0.3%-0.5% of the dry matter during the vegetative stage of growth.” {right in line with the K-Lite concept} “The probability of phosphorus toxicity increases at contents higher than 1% in the dry matter.”

And…

“Often, the chlorophyll content is even increased under phosphorus deficiency, and leaves have a darker green color as cell and leaf expansion are more retarded than chloroplast and chlorophyll formation.”

However, there has also been some evidence that the photosynthetic efficiency per of chlorophyll is decreased in P-deficiency.

So I guess it all goes back to finding that “Goldilocks” point, which studies indicate is pretty low for phosphorus.

I also took a look at the section on Diagnosis of Nutritional Disorders by Visible Symptoms. Purple pigmentation of the undersides of leave is apparently not a symptom of phosphorus deficiency, and he made a couple of interesting statements that opened my eyes a bit:

“As a rule, nutritional disorders that inhibit growth and yield only slightly are not characterized by specific visible symptoms. Symptoms become clearly visible when a deficiency is acute and the growth rate and yield are distinctly depressed.” Considering the slow growth rate and accompanying slight nutrient demand of orchids, it seems hard to imagine the purple coloration is nutrient related at all. This next statement supports that:

“Furthermore, many annual and perennial plant species of the natural vegetation, particularly those adapted to nutrient poor sites, adjust their growth rate to the most limiting nutrient and, thus, visible symptoms do not develop.”

[K-Sci]

[QUOTE=Ray;973151]
Those dry tissue analyses I have seen show them to be about 90% C, O, H, & N, with the N being anywhere from 1.5 to 3% of the mass. P, K, S, Ca, & Mg total about 9% of the mass, with each element being a fraction of the nitrogen content. Everything else makes up that last 1%.
[quote]
The chemical composition of dried orchid tissues performed by a Naik & Barman (2007) found:

Nutrient Weight of dry matter ( g/kg )
Calcium 14.3 – 38.3
Magnesium 2.4 – 28.4
Potassium 3.2 – 14.3
Nitrogen 2 – 8.7
Phosphorous 0.3 – 2.3
Sulphur 0.16 – 0.86

The wide ranges given in this data make this data hard to interpret.

I remain skeptical, however, that the ratios of nutrients in plant tissues indicates the ideal ratios in applied fertilizer solutions.

-Keith---------- Post added at 09:25 PM ---------- Previous post was at 08:51 PM ----------

Originally Posted by Ray

“Furthermore, many annual and perennial plant species of the natural vegetation, particularly those adapted to nutrient poor sites, adjust their growth rate to the most limiting nutrient and, thus, visible symptoms do not develop.”

This appears to be very much the case when nitrogen is the limiting nutrient, but definitely isn't the case with, say, Calcium.

I'm not sure what was meant by "visible symptom", but a slow growth rate is something most people would consider a "visible symptom. Failure to thrive is a problem that commercial growers (and hobbyists) notice and usually consider unacceptable.
-Keith

[Ray]

Keith, those number are quite confusing. Nitrogen is, by, far the most prevalent nutrient element in just about any plant.

But, as has been driven home by several truly knowledgeable folks, tissue analysis tells you what the plant has been getting, and nothing at all about what it needs.

As far as fertilizers are concerned, to my mind, there cannot possibly be an “ideal formula”, as nutrient demands are quite variable.

I cannot speak for others, but K-Lite’s formula was not based upon tissue analysis at all. The role of accumulating potassium was speculation based upon two, totally disparate, non-plants facts - one biological and the other totally inorganic. A little searching of the literature however, supported the concept in plants, and was further backed-up by chemical analyses of the initial rainfall reaching epiphytes in tropical rainforests.

Based upon that info, a lot of folks started experimenting, and in about 2 weeks, we’ll reach the ten-year point in that experiment, and I’ve yet to hear any reports of issues that can be attributed to the fertilizer formula.

[K-Sci]

Originally Posted by Ray

But, as has been driven home by several truly knowledgeable folks, tissue analysis tells you what the plant has been getting, and nothing at all about what it needs.

I agree. What we can conclude from tissue studies is that the elements in the tissues must be available from water, fertilizer, or the media (i.e. plants don't do fission or fusion).

As far as fertilizers are concerned, to my mind, there cannot possibly be an “ideal formula”, as nutrient demands are quite variable.

I completely agree here too.

I cannot speak for others, but K-Lite’s formula was not based upon tissue analysis at all.

You bring it up often in discussions of K-Lite and plant nutrition. That's the reason I expressed doubt that tissue analysis tells us much of any use.

The role of accumulating potassium was ... further backed-up by chemical analyses of the initial rainfall reaching epiphytes in tropical rainforests.

This tells us that these epiphytes can survive and reproduce successfully in nature with very low levels of N/P/K/Ca/Mg/etc. It does not tell us that these low levels are best for greenhouse or home culture. I suspect you will agree that most orchids grow bigger, faster, and flower more profusely with nutrient levels far higher than in the rain forests. If so, the questions become:

1. What levels of the other nutrients must accompany the higher levels of nitrogen to prevent vitality from being limited by these other nutrients.
2. What levels of these other nutrients are to some extent toxic.

These two levels, sufficient and toxic, appear to allow for a very wide range of the nutrients to be beneficial in greenhouse and home culture. People are successful using ratios such as 10-10-10 and even with bloom boosters that are as P-rich as 10-52-10.

Based upon that info, a lot of folks started experimenting, and in about 2 weeks, we’ll reach the ten-year point in that experiment, and I’ve yet to hear any reports of issues that can be attributed to the fertilizer formula.

That may be, but isn't it also fair to say that the much higher levels of P and K widely used by commercial greenhouses for many more decades have not resulted in issues that can be attributed to those fertilizer formulas. The only one I can think of is the expense of using unnecessary nutrients.

For what it's worth, I've seen far more evidence than I need to very confidently conclude that KelpMax promotes strong root growth and that used as directed it is very beneficial to orchid growth. I am also confident that the higher levels of Ca and Mg in K-Lite are beneficial, if not essential, to good culture for people like me using water with low levels of these elements. This is because I've seen the symptoms of the resulting deficiency.

On the need for added Ca and Mg and the benefits of KelpMax I have no doubt whatsoever.

On the other hand, I see no evidence that using K-Lite produces noteworthy benefits to orchid growth beyond those from the added Ca and Mg. In fact, I also do not recall seeing you claim that any such benefits have been shown. As a result I've concluded that the very low levels of P and K in K-lite are at best an unnecessary risk compared to more conventional fertilizers, such as MSU.

For the forgoing reasons, I've stopped using K-Lite. Just as shadeflower has observed, after using it my orchids came to exhibit purple color that I have not seen kin the past. I have not concluded that the purple color indicates a nutrient deficiency, but there is a study on vanda where purple color and other undesirable symptoms were caused by very low P or K (I'm not recalling which). I'm not saying that K-Lite causes any problems whatsoever, but it is an outlier in P and K levels with no evidence I'm aware of that this benefits the plants. I will also acknowledge that I'm by no means an expert on this topic and that my conclusions may be the result of my ignorance on the subject.

-Keith

[Ray]

Originally Posted by K-Sci

I suspect you will agree that most orchids grow bigger, faster, and flower more profusely with nutrient levels far higher than in the rain forests.

Absolutely. I think that's the difference between a subsistence diet and a healthy one. But...again, it says nothing about the ratios.

These two levels, sufficient and toxic, appear to allow for a very wide range of the nutrients to be beneficial in greenhouse and home culture. People are successful using ratios such as 10-10-10 and even with bloom boosters that are as P-rich as 10-52-10.

Unfortunately, we know little about the true uptake dynamics, which is bound to have an impact. I just recently read an article from some college extension service that talked about how calcium, magnesium and potassium are taken up in an uncontrolled fashion if they are in solution, how they can compete for "capture sites" (my term) within the plant, and how overdoing any of them can cause issues due to the "blocking" interference they can cause. That is, too much of any of them can result in a deficiency in the others.

Phosphorus is a whole different case however, as the plant will take up as much as it can get, whether it needs it or not.

That may be, but isn't it also fair to say that the much higher levels of P and K widely used by commercial greenhouses for many more decades have not resulted in issues that can be attributed to those fertilizer formulas. The only one I can think of is the expense of using unnecessary nutrients.

I think we have to consider that most commercial nurseries don't actually keep plants around for very long, precluding the potential issues, and the breeding stock plants they do grow long-term get repotted regularly, thereby dumping the accumulated minerals in the medium.

Cool discussion - Happy Thanksgiving!

[K-Sci]

Originally Posted by Ray

I think we have to consider that most commercial nurseries don't actually keep plants around for very long, precluding the potential issues, and the breeding stock plants they do grow long-term get repotted regularly, thereby dumping the accumulated minerals in the medium.

Cool discussion - Happy Thanksgiving!

I think there are three types of commercial greenhouses. Those that buy established plants for resale (there are a lot of these now), those who grow orchids from seed then sell them to greenhouses of the first type, and finally, cut flower growers. There are many fewer of the latter than there used to be, but they would be on the front line when it comes to fertilizer ratio selections.

I agree, this is a very interesting discussion. Shadeflower's research kicked off this thread with a lot of studies and evidence I've found to be very enlightening. Some of his statements along the same lines have, in the past, received a cool reception and I was among those who questioned some things he said. Over time, I've come to see that there is vastly more hard data behind those statements than I initially realized. The studies he provided support some very interesting conclusions that run very contrary the conventional wisdom.

-Keith