# yellowing leaves on some species



## Paul (Nov 24, 2015)

Hi, I come to you as I have no explanations to my problem.

I have some species that were growing well until last year, and now slowing becoming more yellow and not growing anymore. The roots are not rot, they are good. I fertlize at quite low rate (and give the heavy feeders some slow release fertilizer, no problem for them). Not a problem of too much light as freshly deflasked plants seem to grow with no problem. 

anitum, sanderianum, lowii, dianthum and others are now more yellow than previously and don't grow as fast as before.

I give them a complete fertilizer (akerne rain mix), with all N as nitrate, high Mg, neutral pH and add a little kelp extract in the water.
EC is about 250µS/cm

one year ago, I was fertilizing with home made fertilizer, NH4N03 based with same pH and EC, but much lower K. 
I have changed as many species, especially Catts or Dendrobium were not growing well. 

so do you think there could be an issue with that or may I find another explanation?


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## gonewild (Nov 24, 2015)

Paul said:


> I give them a complete fertilizer (akerne rain mix), with all N as nitrate, high Mg, neutral pH and add a little kelp extract in the water.
> EC is about 250µS/cm



How often?



> one year ago, I was fertilizing with home made fertilizer, NH4N03 based with same pH and EC, but much lower K.
> I have changed as many species, especially Catts or Dendrobium were not growing well.



Change the ones that are not growing well now back to the fertilizer you used one year ago when they were growing well.



> so do you think there could be an issue with that or may I find another explanation?



Not all species or genera require the same nutrients. Seems like you have identified two different groups of orchids that prefer different nutrients.


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## Paul (Nov 24, 2015)

The plant stops growing, then the leaves start yellowing very slowly (6 months at least, I have checked photos of anitum nov. 2014 and spring 2015, then now). 
I fertilize once a week, once every other week in winter months.

Not all the species are affected: emersonii, hangianum, anitum, dianthum, one lowii, one micranthum and some others. medium looks ok and is not old (Orchiata power)

I don't know if it's question of nutrients or pH?


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## SlipperKing (Nov 24, 2015)

I was thinking the same; a need to supplement with a little ammonium based N


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## gonewild (Nov 24, 2015)

Paul said:


> The plant stops growing, then the leaves start yellowing very slowly (6 months at least, I have checked photos of anitum nov. 2014 and spring 2015, then now).
> I fertilize once a week, once every other week in winter months.



Do you water between fertilizing once per week?



> Not all the species are affected: emersonii, hangianum, anitum, dianthum, one lowii, one micranthum and some others. medium looks ok and is not old (Orchiata power)



In pure orchiata? 



> I don't know if it's question of nutrients or pH?



It's nutrients. But it may be that changing the pH will change which nutrients are available.


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## Stone (Nov 24, 2015)

Paul said:


> > all N as nitrate, high Mg, neutral pH
> 
> 
> 
> ...


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## gonewild (Nov 24, 2015)

Stone said:


> Paul said:
> 
> 
> > I believe most Paphs should not be fertilized in winter but you can spray a couple of times with urea to get back some colour?
> ...


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## Stone (Nov 24, 2015)

gonewild said:


> Stone said:
> 
> 
> > But growing under lights in a home under consistent conditions there is no winter, keep that in mind. If there is no winter the plants need fertilizer.
> ...


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## gonewild (Nov 24, 2015)

Stone said:


> gonewild said:
> 
> 
> > Yep true. That's why I said most. But even so I still think that mature plants of the continental species should be rested in winter for long term health.
> ...


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## Justin (Nov 24, 2015)

Agree--try Urea instead of Nitrate...


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## Bjorn (Nov 25, 2015)

Stone said:


> Paul said:
> 
> 
> > If the roots are good, this is probably your problem. You may have a build up of nitrate in the leaves and not enough light to convert it. You should use nitrate and urea 50/50 or at least nitrate ammonium urea 50/25/25 during summer. Paphs love urea! The best colour and health I have seen in Paphs always have urea in their fertilizer. You must be careful with ec readings of course!!
> ...


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## consettbay2003 (Nov 25, 2015)

Bjorn said:


> Stone said:
> 
> 
> > I had the same thought, as I experienced much of the same when I used nitrate N only- some years back. My remedy was to introduce urea as the main source of N. Later, which means this year, I have not been using urea but ammonium (sulphate) as the main N-source. Urea or ammonia is more or less the same the way I see it since urea decomposes to ammonia and CO2. The plants may get greener with urea, but the do not stop growing or get bleached with ammonium (as they will with nitrate only). This sensitivity to nitrate could be a sign of molybdenum deficiency, but think it is better to just spray with a1% solution of urea and see what happens. Or swith to a urea based fertiliser- of course.
> ...


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## Bjorn (Nov 25, 2015)

consettbay2003 said:


> Bjorn said:
> 
> 
> > Could the 24% sulphur in ammonium sulphate cause problems with constant use?
> ...


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## Paul (Nov 25, 2015)

Stone said:


> Paul said:
> 
> 
> > If the roots are good, this is probably your problem. You may have a build up of nitrate in the leaves and not enough light to convert it. You should use nitrate and urea 50/50 or at least nitrate ammonium urea 50/25/25 during summer. Paphs love urea! The best colour and health I have seen in Paphs always have urea in their fertilizer. You must be careful with ec readings of course!!
> ...


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## Bjorn (Nov 26, 2015)

Interesting Paul, how do you see that it is not suited for dendros and Catts? The reason for asking is that I use the same stuff for all my plants including many cattleyas and dendrobiums etc. without seing any problems. And my fertilisation is something like 10:6, N from Ammonia: N from nitrate. (NH4NO3 = 1:1)


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## Paul (Nov 26, 2015)

I see because it grows very much faster and bigger with rain mix at 0,5g/l 
The simple reason is that Catts need high K (and light...) to produce the sugars that make big pseudobulbs... and big blooms.

You can use slow release fertilizer with N=K to boost the growth and bloom (only when the growth has already started)


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