Dendrobium speciosum medium issue

[PuiPuiMolcar]

Hello folks, after reading a few thread about aussie Dendrobium here. I still couldn't figure out what is wrong with my Speciosum.
Issue:
Yellowing leaves and dropping.

Medium: mostly barks
Water: every 4 to 6 days
Light: lightly shaded, with about 3000 to 4000 fc

Further information
When I first got this Den, the leaves were already lightened. It was potted in a semi soil and bark medium while in flower. I repotted after it done flowering, took out most of the brown dead roots and put it in a bigger pot mostly coarser bark medium as I read from its culture sheet. It seems like it can tolerate some dry days but mine is just not doing so good. I'm not sure if need more water or is it have too much water, and i don't want to risk another repot stress.
I live in California zone 10b with mild sunny spring

[estación seca]

That's water and heat/light stress. Fortunately this is a very sturdy species, and there is a good chance it will survive, though it has been set back considerably.

The time to repot Dendrobiums, and almost other orchids, is when you just see new root tips forming. Don't repot at other times. Many orchids only make new roots for a very limited period of time per year. Repotting damages older roots. The plant then struggles to take up enough water until it makes more roots, which might be months away. Most, but not all, orchids make new roots around the time of new growth. If new growth is pushing, the old roots are damaged and new roots don't form, the new growth may die from inadequate water uptake.

You probably cut off normal older roots. Orchid roots start out healthy and white, then turn healthy and brown. The outer velamen layer can be old and thin, even hollow around the root core, and the root can still function. I recommend people never cut off roots. It's OK if dead ones fall off with a gentle shake at repotting. I can't tell for sure what is alive or dead. I don't cut off old roots.

When most Dens are in active growth they prefer a lot of water. This one has a huge natural range, but in many areas it will be wet for much of the summer. For now put it in bright shade to minimize water loss through the leaves. Soak it heavily. Dig down into the bark each day to see whether the bark and the roots are still damp underneath. When the roots are nearly dry it is time to again soak heavily. This might be every 1-4 days, depending on your temperatures and humidity. Every 4-6 days is rarely often enough for a Dendrobium of this type. When you see new growth and new roots, be sure it never dries completely until the growth is fully mature.

Once it has a healthy root system you can gradually move it to more light. Where in southern California do you live? They can take a lot of sun right on the coast, but not as much in the hot inland.

[Keysguy]

My best guess is your issue is the media mix.
Speciosum is a lithophyte and I'm fairly certain our Aussie friends on this board will confirm that in the wild, they are perfectly happy growing right out in day long full sun.
I think the dirt in your media is suffocating the roots.
I have mine in a 50/50 mix of large fir bark and granite chips. There is virtually no sitting water ever unless we have long periods of rain and for me that's only in summer and that's when they want it for new growth anyway. In the right media, your watering regimen sounds fine and maybe cut the light down some while it recovers. It's just a baby.

[Roberta]

The pot may also be too large (but don't repot until you see new growth... which should happen pretty soon) Mine grow in fairly large bark, but tend to outgrow the pot, send roots upward (which may be on the dry brittle side, but are still fine - don't cut!) Yes, they are lithophytes - growing with roots into the cracks of rocks where there is a bit of moisture, sending the rest of the roots out into the air (birds nest roots) where they can capture detritus from the canopy (and get nutrients that way) I have found them to be s surprisingly sun-sensitive. (I have toasted several leaves before I figured out to shade them a bit) I suspect that they grow more in forested areas than in full sun At at least in my back yard, need a bit of protection from the baking summer sun. Medium is very well-drained. Again, their habitat doesn't accommodate a lot of water.

I saw one brought into a meeting that was about 4 feet across, in a pot (shallow bulb pan, 10 inches as I recall) with the bottom cut out and replace with wire mesh, little or no medium. Roots all over the place outside the pot, of course. So the pot was mostly to help the plant stand up and be carried. Any water that it got ran right through,

[PuiPuiMolcar]

Originally Posted by estación seca

You probably cut off normal older roots. Orchid roots start out healthy and white, then turn healthy and brown. The outer velamen layer can be old and thin, even hollow around the root core, and the root can still function. I recommend people never cut off roots. It's OK if dead ones fall off with a gentle shake at repotting. I can't tell for sure what is alive or dead. I don't cut off old roots.

Thank you, I think this might be my biggest mistake. I think you're right, that could be the reason why it is dehydrating a bit too fast.

Originally Posted by Keysguy

My best guess is your issue is the media mix.
In the right media, your watering regimen sounds fine and maybe cut the light down some while it recovers. It's just a baby.

My media current media all bark and the water just flush right through it. I'm getting a feeling it is too airy since the barks are still brand new and they dont absorb enough water.

Originally Posted by Roberta

I suspect that they grow more in forested areas than in full sun At at least in my back yard, need a bit of protection from the baking summer sun. Medium is very well-drained. Again, their habitat doesn't accommodate a lot of water.

Thank you all, I think I will try to give it a shade rest with more attention to watering until it can get back some roots.
The leaves of these guys are stiff as plastic when they dry, pretty crazy.

[stonedragonfarms]

A bit of perspective to build on the rest; to grow speciosum well, it's important to know which variety you are growing--there are 8 [or 9, depending]--or if your plant is an intervarietal hybrid. The majority of varieties are lithophytes, and within these, there is a further specification as to which grows in what type of exposure [ie full sun, partial shade, etc.] and if roots grow directly on/over rock or in humus accumulations on rocks/in rock crevices. The varieties also grow over a wide range of elevations and occur in sites over a 1600 mile range, so there's [literally] a lot of cultural ground to cover.
Some 'general' guidelines though:
1. General light levels are similar to those required for standard Cymbidiums; if you can flower standards, you can flower speciosum
2. There is no hard rule on the 'best' time to repot; some varieties make up new bulbs fully, then push roots [ie v. grandiflorum], some push leads and roots at the same time [ie v. speciosum] & some perpetually push new roots [ie v. hillii]; whenever you decide to repot, make sure to pot for the size of the actual root mass [ie if the plant is in a 4" pot, a 6" pot is going to be about the maximum size for potting on]
3. Stake, wire or tie the plant to stabilize it; newly developing roots are incredibly brittle; if you loose a root tip on one, you're better off trimming the root entirely back--it won't send a side shoot, nor will it uptake nutrients. If a plant is not secure, you run the risk of root damage as the pots sways in the wind [or under circulating fans] or by frequently shifting it about.
4. Stick with medium bark, with a pair of exceptions: a. Seedlings--pot them on in seedling/fine bark [or 50/50 fine & medium bark] & b. FS large varieties [ie v. hillii & v. grandiflorum], use large bark [or 50/50 large & medium bark]--choice of pot material is negligible.
5. Feed regularly when in active growth--if there are actively growing root tips, feed, feed feed
6. Don't sweat it--this species [all varieties of it] are tough as nails; about the only things that will truly do them in are prolonged runs of freezing temperatures or extended periods of drought coupled with extremely high temperatures