Dendrobium jenkinsii bare root mount?

[devaved]

I was recently gifted a D. jenkinsii. It came from the nursery growing naked on plastic mesh and covered in scummy algae.

I cleaned off the algae and divided it to hedge my bets, since some of it isn't looking all that healthy. I plan to post later with pics, but there are small brown sunken spots on the leaves which I believe are pathogenic. Also has tiny white specks on some of the leaves and bulbs which I'm guessing is mineral buildup? but would love some confirmation.

First though: should I leave it mounted as is? The other orchids I've mounted all have a bit of sphagnum, on a surface that retains some moisture. This is bare root on plastic so I'm worried about it drying out.

In my growing area the humidity is ~75% after watering/misting, slowly dropping to 45-50% overnight. There's a small fan running during the day, temp is 75-80ºF day, 68-70ºF night.

I've been misting it 1-2 times a day, aiming for the roots but obviously unable to completely avoid the leaves. Would it be better to stick a bit of moss in there and water it less? The other option would be to cut away the mesh and put it in some moss or bark, but that will involve some root damage as it's thoroughly intertwined with the plastic.

Any thoughts are appreciated!

-deva

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[Roberta]

Photos?
As far as being bare root, that's fine. It needs to dry well between waterings (and in winter, get very little water) It not only doesn't need sphagnum, it doesn't want it. If it has rooted on the plastic, that's great... just leave it. I grow it on cork, completely bare root, it has rooted well and blooms. And I live in a relatively dry climate. When it dries, it really dries. That is what it needs. I normally have 40-50% RH during the day, increasing at night as the temperature drops. But some days, the humidity can be single digits. No problem. Winter night temps close to freezing, summer night temps 65-70 deg F *18-21 deg C) and days typically 85-90 deg F (28-32 deg C(, occasionally higher. This is a tough little orchid.

I don't know if drying or temperature drop in winter are the triggers for blooming (or maybe a bit of both). Mine does get watered in winter - I don't protect it - but it does get the cool to chilly treatment. And dries very quickly. Just what Mother Nature gives it in my neighborhood in terms of temperature, I water because nature provides very little. Actually, I don't dry out most of my Dens in winter and they bloom just fine so I lean toward temperature drop is being more important but I haven't done any sort of study, just what I observe.

[devaved]

Thank you Roberta, that's reassuring.

Here are pics from when it first arrived.

Crusty buildup, which I'm guessing is from tap water:



Some of the spots:


---------- Post added at 04:20 PM ---------- Previous post was at 04:00 PM ----------

These are after I cleaned it up. I put it under tepid tap water and gently scrubbed with a soft vegetable brush, then let it soak in diluted 3% peroxide for a minute (yes I know...) and gave it a thorough final rinse in the sink.

This is a small piece with only those 2 leaves, rest of it is dead roots and shriveled bulbs. See spot on upper side of the large leaf:


and the same leaf, bottom side:

A few of the spots on the main clump:

[Roberta]

Those spots look like old insect damage. just observe, don't worry about treating unless they spread. I think that your humidity is on the high side... again, these need to dry out. And RH should be lower during the day, can go up at night as the temperature drops. But this plant tolerates (and even likes) relatively arid conditions. I think it is sort of a miniature version of Den. lindlei (and a lot easier to flower at my house)

---------- Post added at 01:38 PM ---------- Previous post was at 01:30 PM ----------

Once danger of frost has passed, it may benefit from moving outside. Filtered sun or bright shade - direct sun can burn leaves, but it should be grown quite bright. It comes from mountainous areas of India and southeast Asia so it tolerates wide temperature extremes, a monsoonal climate in summer and drier (but not bone dry) but brighter winters. You certainly have plenty of humidity in summer... all you need is to water it well but don't worry about its drying when the "rain" stops. The species basically thrives on abuse.

All that algae does indicate that it was grown at very high humidity. To me, that's a possible source of bacterial issues... and from experience with my own plant, I doubt that it needs to be that wet. (Mine sure isn't...)

---------- Post added at 02:52 PM ---------- Previous post was at 01:38 PM ----------

If you observe that the plant is showing signs of desiccation, you can add sphagnum OVER the roots. That way you can give them a bit more moisture but you don't have to trash roots by trying to remove them from the existing substrate. I do that with a lot of plants that I mount, such as small Cattleyas, where I want the roots to attach to the mount but need at least a temporary boost to moisture. If you put sphag between the plant and the mount, the roots are much less likely to grow into the mount - they're rather lazy and tend to stay with the sphagnum. But sphag is over the top of the roots you get the best of both worlds - extra moisture, but the roots grab the mount. And it is easy to remove the extra sphag once the plant is established.

[devaved]

Originally Posted by Roberta

I think that your humidity is on the high side... again, these need to dry out. And RH should be lower during the day, can go up at night as the temperature drops.

I don't think my humidity will be a big issue, 75% is what it peaks at right after I water in late morning. Rest of the day it hovers around 50-60%, and there's good air exchange. Plus I'm slowly learning to water less, now that I have enough plants to keep the humidity stable.

I knew RH is a function of temp but I hadn't thought about it in this context. :
It's always ~45% when I check in the morning but it does jump at night! I have a little $12 Thermopro bluetooth hygro, and looking at the log I see that when things cool off at night, RH shoots from ~55% to ~70%. It slowly drifts lower overnight, then drops like a rock to ~45% as soon as the lights come on in the morning.

Originally Posted by Roberta

All that algae does indicate that it was grown at very high humidity.

Agreed, and that's why I was fretting about not having enough! Didn't help that all the mature pbulbs look desiccated, though I'm guessing that was from a winter rest.

In all, it sounds like my conditions are quite adequate. A few brand new leaves have shriveled up and died but that seems likely due to shock. I'll have to keep tabs on those spots to make sure it's not spreading, but I'm much less worried about infecting my other plants. Thanks!

-deva

[Roberta]

Relative humidity is very temperature dependent - the "relative" part is a measure of how much moisture air can hold - and warm air can hold a lot more than cold air. So the same amount of moisture is "relatively" closer to what the air can hold at low temperature (high RH) than when the air is warm (lower "relative" to what the air could hold) The fluctuation (lower by day, higher by night) is a completely natural cycle.

[devaved]

Originally Posted by Roberta

Relative humidity is very temperature dependent - the "relative" part is a measure of how much moisture air can hold - and warm air can hold a lot more than cold air. The fluctuation (lower by day, higher by night) is a completely natural cycle.

Yep! I was just going by what I see on the gauge every evening and morning, didn't cross my mind to think about what might happen in between.