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  #21  
Old 03-24-2008, 06:59 AM
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My first experiments with s/h were in 100% #4 perlite - chunks about 1/2"-3/4", and I later went to 50/50 perlite and charcoal of the same size.

Perlite slowly crumbles over time, giving you this lovely sludge at the bottom of the pot that suffocates the roots.

Charcoal absorbs, but never releases the mineral salts and byproducts of plant respiration, so it eventually becomes a toxic waste dump that has to be replaced.

With the right choice of LECA, you deal with none of the above. Quite a few work well, and some are lousy, depending upon their physical properties.
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  #22  
Old 04-08-2008, 06:05 PM
Pseudo-Scientist Pseudo-Scientist is offline
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Rays online comparison of various leca holds true (see firstrays.com)
While I haven't used his, I've found that all leca/lava rock are not created equal.
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  #23  
Old 04-08-2008, 07:33 PM
kavanaru kavanaru is offline
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and I can add, that since we do not get "PrimeAgra" in Europe (which is already tested by Ray!) I had ti try different LECA brands before starting with S/H. I just did the same kind of experiment Ray shows in his webpage, and I could manage to select two brands which were doing pretty well... My plants are happy
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  #24  
Old 04-09-2008, 01:39 AM
phearamedusa phearamedusa is offline
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Well, I'm probably going to get a lot of flack over this comment. All that the leca is really doing is providing a support to keep the plant upright. It has no nutrient value, as it is inert. You are providing the needed fertilizer when you water. Before you all jump down my throat, I've been in the hydroponic business for 13 going on 14 yrs and growing orchids for most of that time. I have them in coco, bark, diatomite, and even sitting bare root just on the flood and drain table. I have lost some orchids due to moving from an intermediate temp to a more variable temp(moved from an apt. where the temp stayed 70 to 75. into my own house. My orchid room is very variable temp wise, being a small root cellar). I use a 430 high pressure sodium light, or a sunmaster neutral deluxe metal halide depending on what I have going on bloom wise and which bulb I purchased(electronic ballast allows you to use either bulb, no problems).Grodan did make a mix years ago that had rockwool, leca, and possibly chunk perlite in it, but I never used it or sold it so I could be wrong about the exact mix, and I think It was 2000 or 2001. So it may have been Discontinued due to lack of interest at the time.

Diatomite is a newer product that contains soluble silicia, and supposedly retains more water then leca for those looking for another product.

This is just a picture of one plant in flower right now, unfortunately noid but pretty anyways. One other tidbit this is in no medium at all and get watered every other day, the second little orchid tucked in here is just helping to balance the plant in the pot. , Might not be the best pictures, I'll dig out the better camera tomorrow.
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  #25  
Old 04-09-2008, 11:25 AM
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I don't see why you would get flack over that, as most of your post is quite accurate.

In fact, essentially all epiphytic orchid growing is hydroponic, because the potting medium - no matter what it is - is present almost entirely for mechanical support and water & nutrient storage, but does not provide any significant nutrition by itself. In order to do so, the medium would have to decompose, and once that happens we end up with suffocated roots, so we tend to repot before that happens. Moreover, of the organic ingredients used in orchid potting media, osmunda - the roots of one of several osmunda fern species - is the only one that is known to release release any significant amount of usable plant nutrients (especially nitrogen) as it decomposes.

All that said, I got into hydroponics - in the form of semi-hydroponics - as a way to keep my plants alive back in the days when I traveled a lot on business (I averaged 13 flights a week over one 3.5-year period). By using an inert medium, I didn't have to worry about medium decomposition. I ended up with LECA, specifically the PrimeAgra brand, because of it's particular properties with respect to wicking, absorption/release hysteresis, and airiness.

I this case, there are many ways to "skin a cat", and considering all of the other cultural variables we have to deal with, there is no single combination that is perfect for everyone.

On the subject of diatomite, I still wonder about the "soluble silica" claims. Silica, SiO2, is remarkably insoluble in water (I hold Bachelor of Ceramic Engineering and a MS in Ceramics degrees, and am a Corning Glass alumnus). It only becomes significantly soluble if it's in the form of alkaline earth minerals - those based upon sodium, calcium, potassium, and magnesium silicates, for example. I suppose that what makes up the 10% that is not pure silica.

I tried diatomite as a medium in semi-hydroponics quite some time ago, thanks to the generosity of Joe DiDomenico, but had two significant issues with it:
  1. The sharp, angular form of the particles allowed it to pack too tightly, setting up the formation of bridging water droplets, which suffocated the roots. I am confident, however, that had I used a very coarse grade, my results would have improved. (I used a size roughly equivalent to that of the LECA.)
  2. The light color fostered the rapid growth of algae, to the point that it eventually completely choked off the top surface. I was not a regular user of preventive measures (Physan or bleach) back then, so again, things might have turned out better if I had.
Dr. Yin-Tung Wang of Texas A&M published an article in Orchids magazine showing that diatomite did not fully release the minerals in the solutions it absorbed, so expected mineral buildup to become an issue requiring its periodic replacement. Personally, I suspect that's due to the extremely fine microstructure. Its primary industrial use is, after all, as a filter medium!

Besides, everything will have some mineral buildup over time, it's simply a matter of the rate, and that is determined by more than just the properties of the material.
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