Single leaf yellowing?

[spinrah]

Hi all,

One of the upper leaves on my phal orchid has started yellowing and I’m wondering why. It is planted in bark and top dressed with sphag (recently repotted 3 months ago) and I water it about every 4-5 days depending on how the roots look. I was watering initially by immersing the whole pot for 10 mins in water but lately I have stopped doing that as the bark is breaking down. My room temps are about 68-69F and 50% moisture. I have also been fertilizing with 1/16th a teaspoon of k-lite at every watering.

Could this be due to over fertilization or too much water? The visible roots look fine to me.

The leaf is second from the top (2 leaves below it).

[Roberta]

In the first 2 photos (can't tell on the 3rd) it appears that the yellowing leaf is a lower one. So could be force of nature. However, if you repotted 3 months ago and the bark is already breaking down, that's concerning. Fresh bark should be good for a year or two, so you may be keeping it much too wet - the soaking approach would lead to that. Also, the sphagnum would tend to keep things too wet. So, while in general I would recommend against repotting so soon, here it might be necessary to take a look at those roots. Your temperatures are on the low side but not extremely so. Humidity is fine. Remember, the goal in the root zone is "humid air", not "wet". So when you water, it should flow through the pot (pulling air behind it) The 4-5 days interval (a bit under twice a week) is fine if the the mix is airy enough to be drying properly i that time. The fertilizing is fine. Orchids don't need much, that sounds dilute enough for the frequent fertilizing. But I think that it may be staying too wet - not because of too much water, but rather not enough air to dry out. As the medium dries, the water is replaced by air - back to "air" in the root zone being super-important.

The visible roots look to me only so-so. Viable but not great, So definitely concerned about what is inside the pot.

[spinrah]

Thanks Roberta.
Sorry, I should clarify - I shouldn’t have said “breaking down.” What I meant was that the bark is starting to hold more moisture so I don’t want to leave it soaked in water as I had before. But the bark chips themselves are okay. Not the best quality, but they seem to be doing fine.

Here are some photos of the roots inside the pot. This is 4 days since watering. I would typically water it when it looks a little more dry than this (maybe tomorrow).

By the way, this was a grocery store purchase so the roots have looked pretty much like this since I got it - not too great but viable!

[Roberta]

The roots in the pot look good, and the bark is large enough for plenty of air. I'd suggest removing the sphagnum. A really good way to get a feel for the "drying rate" is to weigh the pot right after watering (postal scale or kitchen scale) and note the weight. Then weigh it on subsequent days. When the rate of losing weight slows down (getting pretty dry) it's time to water again. Again, better to water thoroughly (like under the faucet), let it run through the pot, rather than soaking.

[spinrah]

Originally Posted by Roberta

The roots in the pot look good, and the bark is large enough for plenty of air. I'd suggest removing the sphagnum. A really good way to get a feel for the "drying rate" is to weigh the pot right after watering (postal scale or kitchen scale) and note the weight. Then weigh it on subsequent days. When the rate of losing weight slows down (getting pretty dry) it's time to water again. Again, better to water thoroughly (like under the faucet), let it run through the pot, rather than soaking.

Thanks for the weighing suggestion - I'm going to try that!

I initially didn't have sphagnum on the top, but I got a layering effect with just the bark where the top half would dry quickly and the bottom would stay wet. So the sphagnum was supposed to be a solution to that issue. Could it be retaining too much moisture now? I just don't get it cause the inside of the pot looks pretty dry to me after 4 days of watering, but then there's that single yellowing leaf!

[Roberta]

Pot can look dry and still be pretty wet. Tracking the weight will give you a more accurate idea of what is going on. You don't want it to stay wet... there needs to be a wet-drier cycle going on. Since the house is on the cool side, you could also consider a heat mat - it will both keep the plant a little warmer, and also dry out the bottom of the pat faster.

[spinrah]

Originally Posted by Roberta

Pot can look dry and still be pretty wet. Tracking the weight will give you a more accurate idea of what is going on. You don't want it to stay wet... there needs to be a wet-drier cycle going on. Since the house is on the cool side, you could also consider a heat mat - it will both keep the plant a little warmer, and also dry out the bottom of the pat faster.

Ok, thanks. I will keep track of the weight and look into heating mats!

[aliceinwl]

At cooler temperatures infections can be an issue. If the top dressing of moss is staying moist it could be causing problems. My Phals are in bark at similar temperatures. They dry unevenly (top gets dry before the bottom). I just wait until the bottom is dry as well before I rewater.
Uneven drying doesn’t seem to cause a problem. I think that having things quickly dry on top around the stem is beneficial especially if temperatures are on the cool side.

It could just be natural aging of the leaf. But, I’d carefully inspect the stem for any indications of trouble and get rid of the moss.

[spinrah]

Originally Posted by aliceinwl

At cooler temperatures infections can be an issue. If the top dressing of moss is staying moist it could be causing problems. My Phals are in bark at similar temperatures. They dry unevenly (top gets dry before the bottom). I just wait until the bottom is dry as well before I rewater.
Uneven drying doesn’t seem to cause a problem. I think that having things quickly dry on top around the stem is beneficial especially if temperatures are on the cool side.

It could just be natural aging of the leaf. But, I’d carefully inspect the stem for any indications of trouble and get rid of the moss.

I never thought about the trade-off between uneven drying and temperature. Hmm, you make a good point!

Ok, you guys have convinced me to remove the moss.

[Orchidtinkerer]

I like confusing people so I will say leave the moss

No but seriusly a top layer of moss is generally beneficial unless one sees it is staying damp too long but I cannot see that, the roots and even the plant! look on the drier side.

So ask yourselves this, if the plant did not have one little yellow leaf - to me it looks completely healthy - would you be suggesting to change anything?

To me it looks like a root or a flower spike is pushing through the leaves and this can cause part of a leaf to die - it is a sign of good health when a plant is producing lots of new stuff even if it has to break through a leaf to do so.

I would not remove the moss as to me the plant looks perfectly healthy