Dendrobium leaves turning yellow

[Cymbaline]

I inherited this Dendrobium Phalaenopsis at the end of 2017 and it's more than 10 years old. It pretty much remained the same during that time and while under my care until May 2019 when I started getting serious about it's care.

After May it developed this huge new p.bulb (I think that's what they are called) but aborted it's spike. I asked about this here on the board and it was mentioned that the plant probably didn't have enough reserves to expend on it.

Dendrobium Spike stopped growing?


I don't know if this new issue is related because I can't pinpoint WHAT the issue may be. I read suggested articles and still can't figure it out.

Recently the plant's older leaves has started turning yellow pretty quickly and dropping off ( see picture ) and what confuses me is it's growing a new p.bulb which seems like it's going to be much larger than it's parent as it has a much thicker base than it's parent did.

So I'm a bit at a loss of what maybe the issue.
If this is at all possible I would say it seemed to tolerate being pretty neglected for years and it seems to be both thriving under more care and suffering as well.


Previously it was the skinny p.bulb which started having yellow leaves and dropping and I wasn't too concerned about that. I figured plants occasionally have yellow leaves . It never looked very healthy anyways. But now one of the larger ones that always looked pretty healthy has a yellow leaf so I'm concerned .

Any suggestions as to what I should do at this point?

Thank you


What I have observed or checked:

The medium looks good , It was new as of 2018 so I know it may need to be changed out soon but I was going to wait until after the new growth is finished. It doesn't look broken down from what I can tell.


It has a lot of new , large roots but I haven't dug it up to check it's older roots. Maybe I should?


Growing Conditions:

It has a lot more light than it use to. I have it in an East Window and I have grow lights.

I water it more frequently than it use to be but I try and make sure that the pot is dried out before I soak it. I have a bamboo skewer stuck into it's pot and water when the skewer is dry fully dry.

It is given repotme MSU fertilizer once a month and normal water the other times. I recently switched to RO water.

Room is pretty high in humidity I think. Usually 50 - 55% . I have two humidifiers and it sits over a tray of water. It's more humidity than what it was above my kitchen sink for sure.

[Roberta]

If it was potted last year, it shouldn't need it again. New roots sound great, don't worry about old ones since you aren't over-watering. Sounds like your regimen is good. When new pseudobulbs are larger than the old ones, that's an excellent sign. If it loses some old leaves just force of nature, they don't last forever. If the MSU fertilizer is the pure water type (containing calcium and magnesium) you should not have a deficiency problem. If it was of the well-water type you could need a cal-mag supplement. So look at what's on the label. The only thing I can think of is that you might be able to increase the watering somewhat, since it's getting more light. (More light leads to more growth, which leads to more water and fertilizer use) Orchids don't grow fast, so that fat new pseudobulb will need some time to mature. But the long-term prospect for flowers seems to me quite good.

[Cymbaline]

Originally Posted by Roberta

If it was potted last year, it shouldn't need it again. New roots sound great, don't worry about old ones since you aren't over-watering. Sounds like your regimen is good. When new pseudobulbs are larger than the old ones, that's an excellent sign. If it loses some old leaves just force of nature, they don't last forever. If the MSU fertilizer is the pure water type (containing calcium and magnesium) you should not have a deficiency problem. If it was of the well-water type you could need a cal-mag supplement. So look at what's on the label. The only thing I can think of is that you might be able to increase the watering somewhat, since it's getting more light. (More light leads to more growth, which leads to more water and fertilizer use) Orchids don't grow fast, so that fat new pseudobulb will need some time to mature. But the long-term prospect for flowers seems to me quite good.

It was potted around June, 2018 not in 2019. The attached picture is how I inherited it, with both being in the same pot and about end of June, 2018 I separated them into their own pot and fresh medium.

I was going to wait until after this new p.bulb finished growing before I repotted again. Do you think that would be okay? So it's about 2 years which I thought was about the limit.

[Roberta]

I think that you can wait another year before repotting. I usually do closer to 3 years. A lot depends on how wet the medium stays. (Paphs and Phrags, which like to be kept pretty damp and live in small bark benefit from yearly repotting. Catts in large bark in open baskets can go 4 years if they don't outgrow the basket first) Since you are letting it get pretty dry before watering, the medium should be in good shape for another year, I strongly suspect.

[Cymbaline]

Originally Posted by Roberta

I think that you can wait another year before repotting. I usually do closer to 3 years. A lot depends on how wet the medium stays. (Paphs and Phrags, which like to be kept pretty damp and live in small bark benefit from yearly repotting. Catts in large bark in open baskets can go 4 years if they don't outgrow the basket first) Since you are letting it get pretty dry before watering, the medium should be in good shape for another year, I strongly suspect.

Thank You very much for your advice and time regarding this. I'll up the watering a bit as advised too.