Pale yellowish leaves - why????

[Arne]

I don't understand this disbelief in urea and I also think that AOS should modulate their comments about urea. I think urea works quite well most of the time as long as we aren't talking about mounted plants.

 

[Ray]

Thank you all for your above comments. I use K-Lite from First Ray's, 150 ppm weekly. In the winter, I reduce the ppm to 75. I add the First Ray's kelp 1 tbsp/gallon monthly. I grow on 2x4 ft shelves, under two 2-bulb LED shop lights (so 4 bulbs per shelf) and the plants are about 8" from the light. 12 hours a day in summer, 10 hours a day in winter.

Maybe my lights are too close to the plants.

I occasionally give Epsom salts, 1 tsp gallon. Does that really work to green-up foliage? It's never seemed to make any difference that I could tell.

If I am correct that the "150 ppm" is TDS, that means you're applying about 20 ppm N weekly in the summer and only 10 ppm N in winter. Your plants are starving. By contrast, I am applying about 5x that.

Yellowing is actually more common in the case of a nitrogen deficiency than that of magnesium.

If that TDS is determined by a TDS meter, they are notoriously inaccurate and often overestimate the true TDS, exacerbating the issue.

 

[NYEric]

Too much light. Add cal- mag. Less light.

 

[Ray]

I don't understand this disbelief in urea and I also think that AOS should modulate their comments about urea. I think urea works quite well most of the time as long as we aren't talking about mounted plants.

In my opinion, the AOS is really targeting the simple, hobby grower more than the enthusiast, so has for a long time taught in generalities. True enthusiasts - and I think that the vast majority of us here fall into that category - understand that each orchid is its own version of "Goldilocks", with its own set of "just right" in every aspect of its culture.

Orchids can take up nitrogen directly whether it is a nitrate or an ammonium ion, or urea.

Roots take up nitrates and ammoniums more efficiently than they do urea. Leaves take up urea more efficiently than they do nitrates and ammoniums.

While I don't have a lot of first-hand experience, a few knowledgeable folks and my gut tell me that "some of each" is a good idea.

 

[PeteM]

In my opinion, the AOS is really targeting the simple, hobby grower more than the enthusiast, so has for a long time taught in generalities. True enthusiasts - and I think that the vast majority of us here fall into that category - understand that each orchid is its own version of "Goldilocks", with its own set of "just right" in every aspect of its culture.

Orchids can take up nitrogen directly whether it is a nitrate or an ammonium ion, or urea.

Roots take up nitrates and ammoniums more efficiently than they do urea. Leaves take up urea more efficiently than they do nitrates and ammoniums.

While I don't have a lot of first-hand experience, a few knowledgeable folks and my gut tell me that "some of each" is a good idea.

I agree. I rotate between the two sources with multiple brands to cover all the bases.

 

[Tony]

I'm glad my plants don't know how to read AOS caresheets.

 

[Happypaphy7]

Move those two HCMs to natural light and bright shade. If they turn darker green in the next couple of weeks, you will know it was the light.
I don't know why but some of my paphs would bleach out within a week being placed under artificial light (T8). When I moved them out of the light, the normal leaf color returned. Just a thought. You have nothing to lose.

Regarding urea, I agree with a couple of other members here.
The AOS information is absolutely outdated and needs to be updated as it is just outright wrong.
Plants including orchids grow very well with urea.

 

[gego]

I just checked the AOS website just to make sure that the World was still spinning on its axis! It is. They distinctly recommend a fertilizer without urea for all orchids. The only exception is terrestrial orchids because organisms in the oil help the orchids to break down the nitrogen based urea so that the orchid can utilize it.
They suggest an even strength fertilizer like 20-20-20 with trace or micro nutrients. Orchids grown in bark mixes for example can not handle urea based nitrogen.

Check 20 20 20, most of N are Urea

 

[Roth]

Check 20 20 20, most of N are Urea

Unfortunately not anymore...

There are many 20-20-20 and 20-10-20 that are urea free lately, that's why it is important to read the label. Urea free are a sure receipe for disaster.

 

[Ray]

Urea free are a sure receipe for disaster.

That seems like a “the sky is falling” comment to me. I have plants that have not seen a spec of urea in over 25 years, and have not seen any “disasters”.

I am not arguing that urea may not be beneficial, just that it may not be as critical as you stated.

 

[Roth]

That seems like a “the sky is falling” comment to me. I have plants that have not seen a spec of urea in over 25 years, and have not seen any “disasters”.

I am not arguing that urea may not be beneficial, just that it may not be as critical as you stated.

For many species, urea or ammonium are critical to the life of the plants. That's why many species were sold in massive numbers, but are now great rarities in collections... not only Paphiopedilum by the way.

There are quite a lot of species, and some hybrids, that are fully unable to use nitrate as a nitrogen source, as a fact... Some need a mix, ammonium and/or urea for the bulk of the nitrogen, nitrate to join the cation uptake.

After that, there is the speed. A Paph, rothschildianum well grown blooms once per year, wardii twice, coelogyne should do 3 bulbs per year on average, etc... Below that, it is a clear nutrition problem.

 

[gego]

Unfortunately not anymore...

There are many 20-20-20 and 20-10-20 that are urea free lately, that's why it is important to read the label. Urea free are a sure receipe for disaster.

Well at least more on ammonium. I can't see how you can have that mix in pure nitrate.
For me the plant does not know what form of N we are feeding. They all can be absorbed. It is the effect on the pH around the roots that makes the difference. Like what you said, maintain the pH...as simple as that.
I should say, don't read my post, they should read yours...diligent ly.

 

[Ray]

@Roth Would you have an estimate of about how much urea one might want the nitrogen source to be?

MSU RO and Rain Mix are about 95% nitrate and 5% ammonium, and a friend claims he sees a great benefit with adjusting that to 90/5/5. I'd be wary adding more, as being a 46-0-0, urea can load up the N quickly.

 

[Brabantia]

Do you remember this PDF from Floricultura Holland:
https://www.floricultura.com/media/3754/paphiopedilum_pot_plant_en.pdf
Peters 20-20-20 (plenty Urea) mixed with Calcium nitrate. The ratio 6 parts 20-20-20 and 3 parts Calcium nitrate leads to a NNitrate to NNH3 ratio of 0.83 . More ammoniacal nitrogen than nitric nitrogen. The Dutch add a little Magnesium sulfate as Magnesium and Sulfur source.
This is how professionals grow their Paphios.

 

[Brabantia]

Deleted

 

[Guldal]

I occasionally give Epsom salts, 1 tsp gallon. Does that really work to green-up foliage? It's never seemed to make any difference that I could tell.

It certainly does - but of course not if the plants continuously are exposed to too high a light levet!

 

[Ray]

I guess Roth doesn’t have the answer.

@Brabantia - just because they grow that way does not mean it is the only “right” way.

 

[Roth]

I guess Roth doesn’t have the answer.

@Brabantia - just because they grow that way does not mean it is the only “right” way.

I do and I gave it already many times.

A lot of orchid species are unable to assimilate nitrate as a nitrogen source... The correction adding some urea/ammonium would provide those plants with nitrogen as the sole source, but it would be a benefit overa poor formulation already. Urea/ammonium with proper pH control at the roots is the optimal option.

They are not unique plants like that. Blueberries are very famous for being unable to process nitrate correctly...

https://blueberries.extension.org/blueberry-fertilization/
Just a simplified version, there are dozens of research.

Some orchid species and hybrids do not have nitrate reductase at all, some barely, it can be an entire section of a genus, some specific species, or even some lineage vs. others.

That explains why about 4/5 of all the orchid species once in cultivation are not present anymore in any collection. This is not an overestimate, but the mere truth... Out of all the species introduced in cultivation, sometimes in massive numbers, Paphiopedilum sangii, Dendrobium decockii, 99.999995% of all the rothschildianum seedlings ever made, etc, etc... maybe 10% are still alive today, I am not even sure of the figure.

Actually to take an exampple, out of many tens of thousands of rothschildianum from Norris Powell, the Orchid Zone, Tokyo Orchids if not way more, I think there are 200 or less plants alive in the world today, and that may even be an overestimate. It is time for many to question their belief in the plant nutrition and culture...

 

[Ray]

I do and I gave it already many times.

I was referring to the recommended ratio of nitrate:ammonium:urea.

 

[Roth]

I was referring to the recommended ratio of nitrate:ammonium:urea.

Depends on the potting mix and the user's skills to control the pH in the media.

A quite safe option is a 1/1.5 to 1 NO3/NH4 with minimal risks in terms of pH drift.

Many nurseries use a 80-90% urea fertilizer for their Paphs ( all of Taiwan so far...), remaining is nitrate and ammonium...

Japan, they usea 2:1 ratio quite frequently of ammonium to nitrate, some use pure ammonium ( MagAmp-K...)

For me use at least 2:1 NH4 to NO3 ratio, and I increase the nitrogen part a lot with high light/summer/etc... using urea on top.