Yellowing Dendrobium Leaves

[aiyaiyaii]

A few leaves on my poor Dendrobium are starting to turn yellow, and I have no idea why. The weather has gotten colder here in Texas but the temperature in the house stays around 70 degrees. It's planted a "Dendrobium Classic Orchid Mix" containing: Coconut Husk Chips, Medium Hydroton, Granite Chips, Small Sponge Rock, and Pea Gravel. I water and fertilize weakly every 10 days. It was doing fine until the last time I watered it and then the leaves started to turn yellow. I sprayed the medium with Physan 20 a few days ago but the larger leaf is getting worse. The plant was sitting in a humidity tray until the last few days. I mist the orchid from time to time. Could this be from over-misting? Any and all help is appreciated!

[jsehorn]

Looks like dehydration to me. This could be caused by underwatering, or it could be caused by overwatering which leads to root loss, making the plant unable to take up water, which results in dehydration. I could be wrong.

[otis 226]

It could be what Jeff mentions, or possibly they could just be older leaves going into a natural decline. I'm not sure what type of dend we're talking about here, although it does look like one of the so called hard cane varieties. I've been ploughing through the book 'Dendrobium and it's Relatives', great book, but it gives me a basic idea just how many there are and how diverse the family is.
I guess checking the roots out would be the first order of business. If they are rotted, that's too much water, if they look all dried and dessicated, that's most likely too little. It they are white and healthy looking, again, it may just be some leaves dying naturally. I'm sure someone with a lot more experience will be by soon to help you out more.
Best,
Tony

[syndywindy]

I grow a lot of dens and whil it's hard to tell for sure in your pictures, it looks like you have a phal type den. The medium looks awfully dry to me. If you are only watering every 10 days, I think you probably need to increase the watering. This type of den I don't let dry out completely. Mine are indoors for the winter and I am wating mine every 3 days and they are growing in a medium bark and charcoal mix with a bit of perlite thrown in. It is possible that it is just losing it's leaf naturally, they will lose a leaf here and there, but I'd try increasing the waterings. How are the roots of the plant? Have you checked them recently to be sure there is nothing going on below the medium?

[aiyaiyaii]

Thank you all for your input and advice! I checked the roots a few weeks ago, and at first I thought the roots were rotting because they were brown, but I believe it's just pigment from the bark it was planted in before I repotted it. The roots were firm and not mushy at all. I received the orchid as a gift and threw away the tag that came with it, so I don't know for sure what type of dendrobium it is, but I also think it is a phal type den. I'm going to include a picture of it when it had blooms. I'll try to water it more often and see if it gets better. The smaller leaf with yellowing is starting to develop a small brown spot. I hope it's nothing serious!

[minhnhattung]

U grow it with?

[syndywindy]

Ok, it is a phal type den. I would try increasing the water and give it good light and see how it does.

[aiyaiyaii]

minhnhattung - I'm sorry, I don't understand your question. The original post lists the components of the medium its grown in. Unless you are wanting to know what kind of fertilizer I use?

Syndywindy - I watered the plant again two days ago, and although the rest of the plant seems fine, the larger leaf is now almost entirely yellow and the center is turning a orange-brown color. I've attached a picture but it is not true to color. Is this normal if the leaf is dropping naturally? The weather here has been very cloudy and cold so I have not been able to increase natural lighting for it.Thanks for your help!