Problem with yellow leaves

[emydura]

Any suggestions what is causing these yellow leaves. Looks like a deficiency problem. Maybe Iron? Most of my plants are fine but some seedlings from a couple of rothschildianum crosses are affected - roths x Julius and Houghtoniae.

 

[big923cattleya]

Have you checked the roots at all? I have a single fan plant that had very little in the way of live root when I got it some 3 months ago. I keep it hydrated on an east facing windowsill and not much is happening with new roots. Yet slowly, but surely, it is losing one leaf at a time.
They start to go yellow and over ten days to two weeks, the leaf is lost. I need to try something different this weekend. Maybe sphagnum???

 

[emydura]

Have you checked the roots at all? I have a single fan plant that had very little in the way of live root when I got it some 3 months ago. I keep it hydrated on an east facing windowsill and not much is happening with new roots. Yet slowly, but surely, it is losing one leaf at a time.
They start to go yellow and over ten days to two weeks, the leaf is lost. I need to try something different this weekend. Maybe sphagnum???

The roots are fine. They have all been repotted recently. The leaves aren't dying. They have been like that for a while. Basically every seedling of my Julius x Roth's cross is affected. Seems strange when all my other plants are fine.

 

[big923cattleya]

Okay, so that eliminates one possibility.

And if nothing else is affected except those of Julius x Roth, then it is not likely to be nutritional I would think.
Could it be nutritional in the sense of the Julius x Roth combination requires more of something? More iron, maybe. More nitrogen, maybe? I hope others have a more concrete idea.