Confused Deciduous Phalaenopsis

[naoki]

For some reason, my Phalaenopsis malipoensis decided that it's time to sleep! I thought that these deciduous Phals usually do not drop leaves under cultivation. I don't know what caused this. There were a couple times I skipped 1-2 watering. It's mounted on Cedar siding with minimal (sphag + live) moss, so I have to water 2x day. Additionally, since it's getting hot, I reduced the strength of light (4 bulbs T5 HO -> 3 bulbs), and reduced the day length from 15 -> 13hrs/day. Since it's growing in a black grow tent, shortened day length caused this deciduousness? Or I wonder if the other orchids making fruits in the same tent may be releasing some hormone (e.g. ethylene?). Does anyone know what is the main cue for these Phals to drop leaves?

It has been growing well for a year, but I noticed slower growth of root tips this spring, and finally dropped the leaves. It's a fairly mature plant, which keep making many flower stalks, but it never flowered in the last year.

Any advise about how to wake it up? One person suggested 10-20ppm BAP (= 6-benzylaminopurine, benzyl adenine) every other day for 3-4 times to wake up Phal. wilsonii. Has anyone used BAP, which is a cytokinin class of plant hormone, on orchids?

This isn't a slipper orchid, but I thought some of you may know about this.

 

[Rick]

I hadn't heard of this species before so needed to look it up.

It looks like a subtle version of lobbii. Which would be pretty close to parrishii.

Do you grow either of those two with different results?

I have parrishii (mounted), but haven't tried lobii. Before cutting K and overall reducing feed rates, my parrishii would frequently drop leaves and often loose roots on a semi cyclical basis. I've had this plant since 2004 or 2005. Since the fert change it hasn't dropped leaves, and gets continued fantastic root growth.

Maybe its the light dose of kelp too, but compared to when I messed with Superthrive, the rate of kelp use (1/4 tsp/gal) doesn't come close to the hormone concentration in ST.

Not sure if leaf drop in this species is due to winter cold "hibernation" or summer heat "aestivation". But excess TDS is a way to tell the plant its "heading for drought survival time, so dump the leaves to conserve water".

 

[naoki]

Thank you for the info, Rick. Yes, it looks similar to P. lobbii, and related to parishii. Olaf posted photos here: http://www.slippertalk.com/forum/showthread.php?t=21265

I have P. lobbii (pots in bark/sphag mix) and P. wilsonii (mounted) in the same growth tent, and they haven't dropped leaves. Well, they frequently drop older leaves, but maintain 2-4 new leaves, which is their natural growth habit, I believe. The attached photos of these two are from 1 year ago (I don't have an access to photos of P. malipoensis now). All of them have been growing at a fairly decent speed until recently, and they are all active root growers. When P. wilsonii slowed down about 6 months ago (and showed a bit of dehydration), I laid the mount horizontally, so the water is available for a longer time. Then it resumed the growth after a month (without completely dropping the leaves).

I saw the photo of your beautiful P. parishii. Did your P. parishii drop leaves in a specific time of year (winter), and it comes back after a couple month?

P. malipoensis is from Malipo, China, so I'm assuming that they are winter hibernator.

It is an interesting idea about excess TDS. Indeed, I do use 30-50ppm N MSU twice a day, which is a lot if I think about it now. I was thinking that with the mount without much moss, salt accumulation isn't an issue. I'll use only RO for a while to see what happens before I do more drastic thing like BAP.

 

[Ozpaph]

looks dry from those photos. ? humidity too low???

 

[naoki]

They do look dry, but I think these were the original leaves developped before I got them (this is a photo from last Fall). Since then, those old leaves are gone, roots have grown much better, and the new leaves don't look as dry as the photos. Humidity in the tent is 65% day and 80-90% night, so isn't it pretty reasonable for these Phals? But for the mounted ones, they do dry pretty quickly if they are hang vertically.

 

[Ozpaph]

how often do you mist and water them?

 

[naoki]

I water twice a day in the morning and evening. But I occasionally forget, and it becomes once a day. There were a couple incidents of forgetting around the time when it started to slow down (1-2 months ago).

 

[naoki]

Photos of P. malipoensis after it dropped 3 leaves.

 

[Rick]

It is an interesting idea about excess TDS. Indeed, I do use 30-50ppm N MSU twice a day, which is a lot if I think about it now. I was thinking that with the mount without much moss, salt accumulation isn't an issue. I'll use only RO for a while to see what happens before I do more drastic thing like BAP.

The salt accumulation is actually in the plant and not in the substrate.

Epiphytes are K accumulators given th oportunity.

With reference to a leaf drop triggered by salt increase, that came from a treatise on comparisons of CAM vs C3 addaptations to water availability.