Soilless Media - Flushing Before Use?

So, I have been studying nutrient profiles, minerals, etc. I use RO water, still around 7 or 8 ppm though. When feeding, runoff has appeared a little high. Someone on a forum suggested it's due to suspended plant matter, but it's based on EC, not organic matter concentration I would think.

I use a custom blend, one that is pretty free draining...I use regular Pro-Mix Potting Mix, which is Calcium Carbonate (Lime), Peat Moss, and 10% Perlite. I use Hoffmans Horticultural Perlite. I use Hoffmans Horticultural Vermiculite. I use Light Warrior Seed Starter by Fox Farms.

10 Cups Pro-Mix
5 Cups Perlite
1 Cup Vermiculite
2 Cups Light Warrior

Drains well, has a little vermiculite for a slightly different media that holds water and nutrients in a different way, extra perlite so the roots don't drown with a heavy watering, so I can flush easier and make more frequent tweaks to it's nutrients if I need to. I use a little Light Warrior for the Fulvic & Humic Acids, and some beneficial fungus and bacteria.

After my PPM suspicion, I took some of my dry mix, put it in a cup and flushed it. I got 319 ppm in the runoff and a PH of 6.2 after flushing with 8 ppm ro water with a PH of 5.8.

I think that means I should start using a PH of 5.5 to offset the lime and monitor runoff. After flushing with 4 cups of the same size, I ended up with a ph of 6.4 and a 38 ppm. So I got 90% of the Calcium Carbonate out and whatever other junk might have been there, if any. I might try to flush it even further, I use Cal-Mag, and I'd rather the Calcium to Magnesium Ratio to stay where I want it, at about 3:1.

Does any one else pre-flush their soil? Thoughts?

I'm probably negating the small content of beneficials in the Light Warrior. I have some to add, so it's not a huge deal.

Flushed it all the way down to 18 (8 being in the water). I still cant get the PH to budge. I can put in 5.8 ph RO water and get 6.4, I can put 4.0 RO water in it, 6.4 ph. I probably put a half gallon to a gallon through an 8oz cup.

I did some further testing to the perlite and vermiculite. Both were about 6.0 to 6.2 ph when flushed with 5.3 RO. Perlite and Vermiculite PPM came down to 5-10 ppm within baseline. The first just promix flush was over 500 ppm. With effort, this flushed down close too, but was concentrated with salts, probably from the Limestone mostly.

I would think the plant would still grow ok if you stayed 6.0 to 6.4, but I was shooting for 5.8 - 6.2 and a shift from low to touch higher for flowering.

That was eye opening that the ppm's were so high and the soil is on the alkaline side. A probe style PH meter showed it more 7.0 area, but not sure I trust the thing.

So I could use some help. What are others thoughts on this, who have experience in peat based growing. I guess I should read about coco, never have, can't imagine the price is comparable to pro-mix at 4 cf for $14, making the base of the grow media.

Underground Scientist said:

So I could use some help. What are others thoughts on this, who have experience in peat based growing. I guess I should read about coco, never have, can't imagine the price is comparable to pro-mix at 4 cf for $14, making the base of the grow media.

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As In all your other posts you are making this alot more difficult then it needs to be

lio lacidem said:

As In all your other posts you are making this alot more difficult then it needs to be

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Oh, thanks for criticizing but not providing any insight what-so-ever. I provided a lot of information, yes, but I only asked one question... Does any one else pre-flush their soil? Thoughts? For me, I have to understand the science. I have to be able to have conditions measurable and controllable. My biggest goal here is quality, and if I don't establish a strong baseline, I won't be able to try different things and note a positive effect or negative effect if I don't know where I started.

Actually reading into the subject, the ph is going to work just fine. It's just disappointing to me that I don't have full control.

UndergroundScientist said:

Oh, thanks for criticizing but not providing any insight what-so-ever. I provided a lot of information, yes, but I only asked one question... Does any one else pre-flush their soil? Thoughts? For me, I have to understand the science. I have to be able to have conditions measurable and controllable. My biggest goal here is quality, and if I don't establish a strong baseline, I won't be able to try different things and note a positive effect or negative effect if I don't know where I started.

Actually reading into the subject, the ph is going to work just fine. It's just disappointing to me that I don't have full control.

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The reason you dont have full control over your ph is your soil is buffered with lime which keeps ph proper......I have read all your various threads and still think you are making things way to hard.

lio lacidem said:

The reason you dont have full control over your ph is your soil is buffered with lime which keeps ph proper......I have read all your various threads and still think you are making things way to hard.

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Do you like your PH at 6.4?

If you just planted a seedling, and you water with RO, and your runoff tests at over 300 ppm, is that cool for you?

I realize it is buffered with lime. My point was the ph buffer is raising the salt levels of my mix...I don't like that. I also don't like that I can't influence the ph, even if I try to flush most of the buffer out. I know I am not the only one who flushes their pro mix.

I've been getting a little frustrated, because I started some and ended up with issues. Started getting purple stems and a little yellowing, even some necrotic spotting on the first true leaves with 5-6 nodes grown. I was told specifically by Advanced that extra Mag was not required with their mix even after I said really??? 2.4%Ca 0.1Mg??? Added reasonable ppm ferts, but high ppm run off, and some leaf twisting and drooping. I don't overwater, like 3-5 days apart. So just mag problem? Too Dry with RH below 10%? Too many salts? Lighting Issue(not likely)? Now do you see where my OCD is springing from???

For soil I keep my ph between 6.4-6.8. Leaf twisting with drooping is usually im my experience has to do with ph. Purple stems dont have anything to do with cal or mag imho either.

lio lacidem said:

For soil I keep my ph between 6.4-6.8. Leaf twisting with drooping is usually im my experience has to do with ph. Purple stems dont have anything to do with cal or mag imho either.

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I've read sometimes it's genetics, but red stems with some mild yellowing with necrotic spotting is tell tale Mg. I added CalMag, and new shoots reinvigorated and grew green stems. So I think I was right.

your problem is you are reading the run off, as smart as you seem, reading run off is stupid and really tells you nothing.
I know you'll want a full explanation of this, but I also know you will try and fight me on it, so,No.

lio lacidem said:

For soil I keep my ph between 6.4-6.8. Leaf twisting with drooping is usually im my experience has to do with ph. Purple stems dont have anything to do with cal or mag imho either.

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I HAVE seen purple stems from a deficiency when people use distilled water and/or r/o and their base nute doesn't have enough cal/mag in it.

So basically, I had started a few more, with a different nutrient plan. Checked run off on first watering, over 300 ppm. Flushed it down to 150 including some mild cal mag, voodoo, and pirhana. I may start a couple more, pre-flush the soil, and compare all three runs.

Dr.Nick Riviera said:

your problem is you are reading the run off, as smart as you seem, reading run off is stupid and really tells you nothing.
I know you'll want a full explanation of this, but I also know you will try and fight me on it, so,No.

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Wait, why is reading run off stupid? If I'm getting more ppm's out than I have put in...it seems to be a problem if I want to maintain a specific EC. I have heard a bunch of talk about solids from the soil floating but that doesn't hold up. I've tested water with plenty of soil fines floating around, flushed down to 15 ppm or less.

Underground Scientist said:

Wait, why is reading run off stupid? If I'm getting more ppm's out than I have put in...it seems to be a problem if I want to maintain a specific EC. I have heard a bunch of talk about solids from the soil floating but that doesn't hold up. I've tested water with plenty of soil fines floating around, flushed down to 15 ppm or less.

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first, you're measuring the water that ran past your medium real fast and collected what ever stuff will release easy. Second, IMMOBILE nutrients. 3rd. How do you know WHAT nutes are left behind and what ones ran thru real fast?

Underground Scientist said:

Does any one else pre-flush their soil? Thoughts?

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No, been reusin the same bale of peat for over 7 years

the notions in your head are anti-grow you need to put your ocd on the shelf

RM3 said:

No, been reusin the same bale of peat for over 7 years

the notions in your head are anti-grow you need to put your ocd on the shelf

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If you are reusing your peat, the initial salts in the mix have been flushed out.

You don't flush your peat after growing with flowering nutrients, or do a final flush at the end of your grow?

You may be flushing after all...

Underground Scientist said:

If you are reusing your peat, the initial salts in the mix have been flushed out.

You don't flush your peat after growing with flowering nutrients, or do a final flush at the end of your grow?

You may be flushing after all...

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Do a search on his name, look up make it rain, and boiling water at end. that will answer your questions

Underground Scientist said:

If you are reusing your peat, the initial salts in the mix have been flushed out.

You don't flush your peat after growing with flowering nutrients, or do a final flush at the end of your grow?

You may be flushing after all...

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I don't flush, flushing at the end is a myth and a waste of time, I also have not checked ph in years and have never owned a meter. You are way over thinking things

Dr.Nick Riviera said:

first, you're measuring the water that ran past your medium real fast and collected what ever stuff will release easy. Second, IMMOBILE nutrients. 3rd. How do you know WHAT nutes are left behind and what ones ran thru real fast?

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Ok, now you are saying a few things I can begin to understand. So, by all means, explain the IMMOBILE part. I mean, I know Ca is immobile, and Calcium Carbonate is not a highly available form of Ca for the plant, and I can't just flush it out...nor do I want to flush it all out. I want some buffering ability. My biggest point here is that 300 ppm of material is coming out of an volume of water equal to the container size. What is this? Is it calcium carbonate, is it other salts? Is adding 100 ppm of lightly ammended RO water going to give me an EC in the soil of 400 for a plant that just sprouted, and what effect may this have on newly developing roots?

If I flush most of the unknowns out that come out real fast, I'm going to much closer to being able to just add the nutrient profile that I want to put in.

I know I'm overthinking....but the question remains...does it make logical sense?

Why am I asking and why do I think I need to? I had a mag problem. If calcium is really abundant, and mag is not, the calcium is going to very strongly buffer the mag and the plant won't uptake it like it should. I seem to have had an early mag problem. I need to fix it. I can either flush out the excess Ca, or amend with extra mag early on.

And, is an EC of over 300 cool for a sprout. If that is a 300 ppm of buffers, how is that going to affect the uptake of mobile nutrients?

Underground Scientist said:

Ok, now you are saying a few things I can begin to understand. So, by all means, explain the IMMOBILE part. I mean, I know Ca is immobile, and Calcium Carbonate is not a highly available form of Ca for the plant, and I can't just flush it out...nor do I want to flush it all out. I want some buffering ability. My biggest point here is that 300 ppm of material is coming out of an volume of water equal to the container size. What is this? Is it calcium carbonate, is it other salts? Is adding 100 ppm of lightly ammended RO water going to give me an EC in the soil of 400 for a plant that just sprouted, and what effect may this have on newly developing roots?

If I flush most of the unknowns out that come out real fast, I'm going to much closer to being able to just add the nutrient profile that I want to put in.

I know I'm overthinking....but the question remains...does it make logical sense?

Why am I asking and why do I think I need to? I had a mag problem. If calcium is really abundant, and mag is not, the calcium is going to very strongly buffer the mag and the plant won't uptake it like it should. I seem to have had an early mag problem. I need to fix it. I can either flush out the excess Ca, or amend with extra mag early on.

And, is an EC of over 300 cool for a sprout. If that is a 300 ppm of buffers, how is that going to affect the uptake of mobile nutrients?

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I don't know this word "flush" I am a gardener. The only thing I "flush" is my toilet. I don't over feed, I don't have the medium long enough to have a salt build up, But i would assume you are measuring mostly salts.