Fertilizer build up on s/h medium question

[Becca]

I have a few orchids, out of the many I have potted in s/h medium that continues to have fertilizer build up on the PrimeAgra medium. Some of the build up looks white and some looks kinda like a white crystaline look. I can even see the build up on the roots that are near the top of the medium and many of the roots have died and I am assuming from the build up. I have always flushed my pots with RO water every 4th watering since I have been using RO water, but before I just had city water...yuck. Now I have even stopped using fertilizer with these particular ones in an attempt to flush the pots even more....and I usually flush multiple times....I just can't seem to get the white buildup off my s/h medium or the plants.....should I prepare a different batch of s/h and repot these plants? I am stumped and not sure what else to do.

[IdahoOrchid]

I have seen minor white buildup on my s/h material as well. I do not really think it is your fertilizer that is doing this, but precipitates from the media. I especially think this because it is only happening in select pots and/or areas of the pots.

Try just removing the pieces that show the white buildup and replacing it with fresh pieces.

Put the removed pieces in RO water and let them soak a good while to see if the offending material dissolves away.

[Becca]

I can see some of the medium like this through the holes of the water reservoir as well?

[Ray]

Steven hit the nail on the head:

In order to pelletize the clay to form the LECA balls, various organic- and inorganic binders are added. When the clay is fired, the organic components burn off, but the inorganic components may, or may not, depending upon the firing cycle. Further, in order to cool the pellets rapidly for packaging and to keep dust down, they are typically sprayed with water, and there's no telling what's in that.

That's why I recommend that folks presoak the material for at least 24 hours prior to use, to extract as much of those processing residues as possible. Adding calcium nitrate and/or magnesium sulfate (Epsom Salts) to the soak accelerates the extraction process (it works for CHC, too).

When I have been too rushed to presoak the LECA properly, I see the same buildup, and it's really hard to redissolve, so I merely remove those particles from the top of the pot, replace them with clean ones, and put the "offending pieces" in for a better soak.

It's interesting to note that it's a "double-edged sword" - the fact that you see such buildup from the medium indicates that it is really good at absorbing then re-releasing solutions, which is good for the culture method.

[nenella]

Hi Becca,
you say you've always flushed your pots with RO water every 4th watering ..
I'm no expert & only have 2 phals in s/h for now. I have the same problem and have now started flushing at, nearly every watering... (sometimes I am too lazy to change all the water ). I hope this is will work.

[Becca]

Ray, I would say 99% of the time I pre-soaked for 24 hours or more. If I used a fertilizer solution when watering, would it be ok to flush afterwards with RO water every watering like nenella mentioned or would this prevent the orchids from getting the nutrition they need that would normally be in the water reservoir if it hadn't been flushed?

[quiltergal]

Becca, I flush twice with plain water first and hit it with the fert solution last at every watering. I have no problem with salt buildup at all.

[IdahoOrchid]

Becca, yes, you must flush first then water with fertilizer.

I really think your problem is mostly media precipitation though.

[Becca]

I agree....I trust Ray and Your opinion that it is mostly media precipitation. I was just curious about the flushing process after fertilizing. I am sterlizing some used s/h medium now as we speak so when I am finished with the final soak, I will replace some of the medium with the white stuff on it with the fresh stuff. Thanks for the help!