LECA vs Lava rock - salts accumulation
Hi Ray, hi all,
I saw this post "LECA Comparison Study 2020", I visited the website and I found it very interesting and useful. (I am creating a new thread here as I think that that thread is closed (i.e., it is not possible to post any replies to it)).
I am currently using lava rock with a few Phals in semi-Hydroponics and LECA seems to me a good alternative as it gives me the feeling that it can retain moisture a bit better as it expands a bit with water and that the spacing left for the roots is given with high accuracy by the chosen dimensions of the spheres, while with lava rock it varies as it depends on the irregular size and shape of the rocks. I also assume that LECA weights less; a lava rock pot can become quite heavy...
I have also read many other pages in Ray's website (and I plan to read it all very soon!), including some statements that lava rock is not so good as medium as it accumulates too much salts. I would like to understand the rationale for these statements as:
- If lava rocks accumulates too much salts, why does LECA not? My assumption is that you need a medium with high porosity/surface in order to retain as much water as possible. Since I assume that both LECA and Lava rock are very porous with a lot of surface, if one accumulates too much salts then I would expected that the other would do it as well. Or am I missing something here?
- Since more than a year I am growing a few Phals in Lava rock, with supplemental light in winter, feeding them every week regardless of season alternating two solutions: week#1 Sol a) N 120 ppm and all the other macros in proportion to that; week#2 Sol b) only micros, an so on so forth every week without missing one single week of fertilization. I use RO water and a soak the pot between 12 and 24 hours when I feed the Phals.
My assumption, correct me if I am wrong, is that Sol a) is a bit on the high side for its concentration of nutrients, and this seems also confirmed by the TDS reading of the solution between 600 and 700 ppm. Despite that, I do not see any accumulation of dray salts on the lava rock when the rock dries; Once every couple of months I do the following test: I leave the pot soaked for 24 hours in plain RO water after applying Sol a). The TDS reading after 24 hours is about 15ppm and the the reading of the RO water is 9 ppm: so there is close to zero leakage of dry salts from the lava rock back to the RO water, right?
Maybe, swapping Sol a) and Sol b (the latter has a very low TDS) does the trick flushing every other week the accumulation of dry slats caused by Sol a)? If so, this seems a very easy solution in order to use lava rock without salts accumulation. In addition micros are much more readily available for absorption by roots if they are not mixed with macros (e.g., iron tends to easily precipitate out of solution if PO4 is present in the same solution, especially at high PO4 concentrations). And all the work to get the right PH stuff (i.e., the sweat spot of PH 5.8) really matters only for micros (Phosphorus is even not so available at PH of 5.8). So, by swapping sol a) ad sol b) you get also the following advantages: 1) you test PH only when you feed the micro solution (i.e., less work); 2) you get iron (and other micronutrients) and well as the macronutrient Phosphorus more available to the roots.
I would appreciate very much your thoughts as I want to try soon LECA, but I have first to understand the salts accumulation aspects. I want to be sure I am not missing anything important here. All what I wrote above makes sense to me, but who knows for sure? Not me...
Thx.
Cheers,
Dav
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