yellowing leaves on some species

[Paul]

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?

 

[gonewild]

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.

 

[Paul]

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?

 

[SlipperKing]

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

 

[gonewild]

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.

 

[Stone]

all N as nitrate, high Mg, neutral pH

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!!
Also make sure your Mg is less than half of the Ca most of the time and make sure they get enough sulphate too. 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?

 

[gonewild]

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?

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.

 

[Stone]

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.

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.

 

[gonewild]

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.

Yes probably a winter rest is good. I just wanted to point out that under lights the winter must be created and not just be assumed based on the months on the calendar.

 

[Justin]

Agree--try Urea instead of Nitrate...

 

[Bjorn]

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!!
Also make sure your Mg is less than half of the Ca most of the time and make sure they get enough sulphate too. 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?

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.

 

[consettbay2003]

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.

Could the 24% sulphur in ammonium sulphate cause problems with constant use?

 

[Bjorn]

Could the 24% sulphur in ammonium sulphate cause problems with constant use?

Not that I have seen. I believe that it is more common to see sulphur deficiencies than problems related to it. No, actually I think it is good
However, remember that I just add a total of perhaps less than 100ppm to my water, and I do water quite often.

 

[Paul]

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!!
Also make sure your Mg is less than half of the Ca most of the time and make sure they get enough sulphate too. 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?

Interesting, Stone
The slow release fertilizer I use for part of the plants contains half N03- and NH4+ as N source. And they have grown very well this season.
Now I think I just have to treat my Paphs and Phrags with the home made fertilizer like last year. I have now a more simple formula. I just mix a powder of Magnesium sulfate + 10-52-10 + NH4N03
K is very low (NPK about 15-5-1), but when watering, I add Kelp extract which is high in K (1-3-5 NPK)
About 1g/8L powder + 1ml/8L kelp extract

But it's not suitable for Catts, Dendrobium and other pseudolbulb plants. The rain mix is much better for them so I will now separate the waterings.

 

[Bjorn]

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)

 

[Paul]

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)