Root life expectancy

[MT-Phal]

So I've had my phal in s/h for about a year now, and it is still slowly recovering back to it's old self. See prior posts if you want to see my s/h odyssey. Anyway, I have a handful of new growth that were doing really well up until last week. They were bright green with healthy tips. However last week one of them had a case of that spiderweb-ish mold, and the green velamen was slowly turning dark and black.

I cleaned the mold with a q-tip, physan, and plenty of h2O2, but now the root tip has stopped actively growing and the root is slowly turning dark. The root section before this growth, which grew into and adapted months ago to S/H, is also turning black as well. Do roots have an expiration date? Any ideas what could cause this to happen?

I flush every day, water at 150ppm with fertilizer bought from Ray.

[King_of_orchid_growing:)]

Older roots do die, but it could take years, not days or a few months. This is strictly speaking of epiphytical orchids in general, of course.

[Rhynno]

I've had the same thing happen. I've seen some new roots growing into the medium suddenly just stop and rot. I measured my ph and there was nothing out of the ordinary (can't recall the exact value off the top of my head but I remember looking it up and if memory serves it was ok). I'd be curious to hear the answer !!

[MT-Phal]

hey rhynno,

I'm glad I'm not the only one! So strange...

[johnblagg]

I have had this happen with my first catts in s/h ....

I decided it was actually salt build up from not flushing well enough In my case since almost every time it happened it seems the root had became a bluish color first like it was adsorbing the dye or coloring agent from the fert "My fertilizer has a blue color to it I assume is a coloring agent"...I made my freat mix a little weaker and started flushing better and since I had just a couple s/h chids at the time put them in the shower and after flushing let them sit in the shower and turned to shower on and let them have a rain for 5 or 6 mins as well to carriry away even more built up salts and wash the build up off leaves as well.......in my case it was more the root would just shrivel up and dessicate and die back a inch or so.

[Ray]

I cannot say for sure if you're overfeeding or not, but 150 ppm daily seems excessive. That concentration 2 or 3 times a week is adequate. Why are you watering so often? If it is because the top of the pots are drying out quickly, then I'd look more at the following:

In the specific case of a phalaenopsis, I would also consider that the plant might be being grown too cool. The evaporative cooling from the medium can be pretty significant, especially as the humidity drops, and if you are allowing the plants to get cool at night, the combination might be pushing the root system's limits.

[Izzie]

The evaporative cooling is a good point, Ray. Is there anything we growers in dry climates can do besides use seedling heat mats?

[MT-Phal]

That's interesting, Ray. I'll drop my PPM down to 125 or maybe even lower. I'm curious, though, why is it more excessive to water at 150ppm daily rather than weekly in S/H? I would think that the nature of the medium would mean that if it were too much, it's too much.

And b/c I'm an in-home grower, I don't know what to do to raise humidity short of getting a terrarium which I don't want to do for my single plant. I do have a heat mat, which helps on cooler nights in southern California. Though when this began nights were pretty warm. So I'm puzzled.

[TylerK]

Given that this is continuing to happen to you with this plant, I'm thinking you have some form of bacterial infection probably spread through your pot. If I understand properly what's been happening, your physan applications have been killing off most of the population, but not all of it, and it growing back in time to kill off your newer roots. How often and for how long are you applying the physan?

If it were my plant, I would remove it from s/h and soak the whole plant in physan (or better yet, something more systemic like phyton 27) and then thoroughly sterilize both the pot and the LECA.

[Ray]

Izzy - I have heard of folks putting a layer of sphagnum or even mylar on the top of the medium to slow the evaporation rate, but the simple fact is that if you live in a dry environment and like the ease of s/h culture, you're better off not growing the plants that can't handle the chill, unless you can keep them warm.

MT - With some (not all) plant nutrients, the higher the concentration outside of the root cells, the faster it will be absorbed. No matter what the concentration you use, as the plants takes up nutrients, the concentration decreases in the solution, independent of the medium, unless it sequesters the ions (very little of that happens in any orchid medium).

For the sake of discussion only, let's arbitrarily say a plant takes up 25 ppm N per day, and does so linearly. If I start with 150 ppm N, that means that on day 7 it's at zero (150 to start, 125 a day later, then 100, 75, 50, 25, and 0)., meaning that the plant has been exposed to an average of 75 ppm. If I water every day, that average jumps to 137.5 ppm.

However, I doubt that's your issue. As an experiment, I once fed a tray of phals and a tray of oncidiums 125 ppm N daily for 6 months, and they all grew great, with no issues.

I'm thinking TylerK is on the right track, although if it's a bacterial infection, Physan won't be much use (it's a great disinfectant, but topical only), and neither will Phyton 27, as although it IS systemic, it's a fungicide, not a bactericide.