Root life expectancy

[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.

[TylerK]

According to the Phyton 27 literature, it is both a fungicide and a bactericide and I have used it effectively to treat both. The link below is the Phyton technical bulletin which explains how to use to treat for both bacteria and fungi.

Phyton 27 for orchids

Tyler

[orchids3]

Has anyone checked the pH of the growing media or runoff? I find that a sure way to kill roots is to have pH too low - most orchid growers and a lot of experts I have read - say 5.8 to 6.2 is the right pH but frankly I have my best luck and least root loss at 6.8 to 7. Granular Dolomite Lime does the trick. Use 1 tsp per gal pot.

[MT-Phal]

Thanks for the info, guys. I made a new batch of fertilizer last night, and I estimate the ppm to be around 75. At one point I was using physan once a week, then I dropped off for a while thinking things were okay. I may go back to that routine, though if this is a bacterial/fungus issue it is different than one I've had in the past where my roots had lumps.

In this specific instance though, it is only one root and it seems okay for now... the mold is gone and the newer growth is still green, though looking sort of transparent. My other roots seem to be doing okay. I wish I had a way of testing PH, but unless someone else here lives in Sherman Oaks, CA and can tell me I'm out of luck at the moment.

[orchids3]

pH test meters are ok but have to be calibrated - mine failed after a couple of years and it was a good one. A pH test kit for aquarium water is what I use now. It is inexpensive and the results are satisfactory. You really need to check and adjust pH.
You can detect things like media breakdown, and excessive high and low pH.
The best uptake of nutrients occours around the pH of 7. If pH is too much higher or too much lower - the plant cannot uptake some of the nutrients in addition roots die at low pH.
We know that too much micronutrients are toxic to plants. Dead roots are also the symptom of a micronutrient toxic reaction. pH shifts may cause this toxic condition ( at least thats my theory and it has passed the test of time in my greenhouse.)