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bobrown14

Grow Journal of the Month: Dec 2017
Science Bomb on "flushing" aka leeching. Pay attention to highlighted area.



Cations can be classified as either acidic (acid- forming) or basic. The common acidic cations are hydrogen and aluminum; common basic ones are calcium, magnesium, potassium and sodium. The proportion of acids and bases on the CEC is called the percent base saturation and can be calculated as follows:




Total meq of bases on exchange sites

Pct. base =(i.e., meq Ca++ meq Mg++ + meq K+)
saturation ------------------------------- x 100
Cation exchange capacity


The concept of base saturation is important, because the relative proportion of acids and bases on the exchange sites determines a soil's pH. As the number of Ca++ and Mg++ions decreases and the number of H+ and Al+++ions increases, the pH drops. Adding limestone replaces acidic hydrogen and aluminum cations with basic calcium and magnesium cations, which increases the base saturation and raises the pH.

Relationship Between CEC and Fertilization Practices
Recommended liming and fertilization practices will vary for soils with widely differing cation exchange capacities. For instance, soils having a high CEC and high buffer capacity change pH much more slowly under normal management than low-CEC soils. Therefore, high-CEC soils generally do not need to be limed as frequently as low-CEC soils; but when they do become acid and require liming, higher lime rates are needed to reach optimum pH.

CEC can also influence when and how often nitrogen and potassium fertilizers can be applied. On low-CEC soils (less than 5 meg/20000g), for example, some leaching of cations can occur. Fall applications of ammonium N and potassium on these soils could result in some leaching below the root zone, particularly in the case of sandy soils with low-CEC subsoils. Thus, spring fertilizer application may mean improved production efficiency. Also, multi-year potash applications are not recommended on low-CEC soils.

Higher-CEC soils (greater than 10 meg/100g), on the other hand, experience little cation leaching, thus making fall application of N and K a realistic alternative. Applying potassium for two crops can also be done effectively on these soils. Thus, other factors such as drainage will have a greater effect on the fertility management practices used on high- CEC soils.
 

Emeraldo

Well-Known Member
Enjoyed reading that, Bob, and not just the emphasized phrases. Soil science is fascinating, and leeching in low-CEC soils is a real problem for farmers in the field. It seems to me this is a problem for the cannabis grower who grows outdoors in the ground, just as it is for the corn farmer. And I have the impression that you grow in the ground near your bog. What does this tell us about growing cannabis in pots at home, where we can mix and test and amend our supersoil?

I don't think cation leeching is foremost in the mind of the cannabis grower who flushes the soil in 15 gallon pots before harvest to improve taste. Or the pot grower who flushes before flowering starts to adjust the plant to flowering nutrients. By washing excess nutrients out of the soil -- and, yes, out of the roots -- leeching might occur. Of course, any cation leeching in my fabric pots might also be compensated next season with amendments of say calcium (your oyster shell mix, of which I bought some for next year, thank you for the tip).

The main issue raised here is the risk of pushing pH down too far. With low-CEC soils, losing Ca and Mg leads to lower pH, which can be corrected with lime. Uncorrected leeching will make the soil in your field too acidic. But when it comes to flushing soil in a 15 gallon pot -- if a grower wishes to flush -- all this simply underscores the need to flush with water having the right pH for the cannabis plant. Flushing with water having the correct pH would minimize the risk of leeching the soil in my 15 gallon pot, which, if it did occur, could be corrected with lime and other amendments for the next grow.
 

bobrown14

Grow Journal of the Month: Dec 2017
Emeraldo,

What you say is true. Leeching is a thing in sandy soils with low CEC and AEC.

What we are doing growing in containers in soil, most are running high CEC soil.
The way to test that is to get a soil sample.

If there's rock dusts in the mix its going to raise the CEC to VERY high levels.

Think about clay and how it is formed and why it's important for healthy soils.

This is why many of us add rock dusts to our soil mix. This is taking the place of a naturally occurring clay / clay mix that are in many soils in the ground around us.

We container growers try and mimic this with our soil mixes.

Another little info bomb:

"What are exchangeable cations?

The clay mineral and organic matter components of soil have negatively charged sites on their surfaces which adsorb and hold positively charged ions (cations) by electrostatic force. This electrical charge is critical to the supply of nutrients to plants because many nutrients exist as cations (e.g. magnesium, potassium and calcium). In general terms, soils with large quantities of negative charge are more fertile because they retain more cations (McKenzie et al. 2004) however, productive crops and pastures can be grown on low CEC soils.
The main ions associated with CEC in soils are the exchangeable cations calcium (Ca2+), magnesium (Mg2+), sodium (Na+) and potassium (K+) (Rayment and Higginson 1992), and are generally referred to as the base cations."


This electrostatic force is why flushing soil to get rid of excess nutrients is basically just washing away the micro-organisms beneficial to plant growth.

The micro-organisms don't have a life boat but they do have hyphae to hold onto. Like a life rope when the floods come. They will come.

I wood say flushing can be of some use. But that wood be when you have your soil tested and know the CEC, AEC and soil pH as tested in a lab along with all your base nutrient levels. Likely be where indoor professional cannabis growing is headed as long as there's money there to support the work.

The thing with soil is most of the nutrients are not soluble and require micro-organisms to break them down into soluble form. Trying to wash them away along with the micro-organisms just doesn't make a lot of sense to me.

Best to start off with a balanced soil and not need to add in nutrients because you're soil mix is lacking something.

Amendments are important.
 

Emeraldo

Well-Known Member
There is a good discussion of flushing in Ed Rosenthal's Marijuana Grower's Handbook (2010), pp. 162-63, where he discusses fertilizer overdoses.

The science here is essentially the second law of thermodynamics, which states that in a solution the concentration of salts becomes equal throughout. In plant tissue, equilibrium is maintained via cell membranes and osmosis. "Normally, plants maintain a higher salt concentration than the surrounding environment so they easily absorb water. When the solution outside the plant becomes more concentrated than the solution inside, the plant cannot draw water and wilts."

That is what happens with a fertilizer overdose. The soil has such a high concentration of salts that the plant cannot absorb water and a nutrient lockout takes hold.

Then Rosenthal says:
"To save plants suffering from toxic overdose of nutrients, run plain water through the system to flush out the medium so the nutrient concentration becomes diluted. When this happens, the porcess reverses and the plant is able to pull water inside, once again become turgid."

This may in fact be what happened to the plant of the OP. It wilted. So where did the heat discussion go? Maybe the plant was suffering from fertilizer overdose!
 

bobrown14

Grow Journal of the Month: Dec 2017
No not in soil.

Osmosis in soil is basically how water evenly distributes. Has nothing to do with fertilizers or salts. Plants have a vascular system to move water and nutrients up thru the plant. That process is capillary action. Pretty cool stuff.


What you quoted goes against all physics and plant biology.

Osmosis in plants works somewhat different than you explain.

Here's how osmosis works in plants:

"Plants absorb water and minerals salt from the soil with the help of root hairs. They absorb water by the process of osmosis. Osmosis is the movement of water molecules (solvent) from a lower concentration solution to a higher concentration solution through a semi permeable membrane "

"toxic overdose" = you screwed up and tried to kill your plant with too much fertilizer.

OK you might be able to save your plant with more water. But it's not removing much nutrients in SOIL OR from the plant. Specially soil with high CEC or even moderate CEC. It would have to be soil-less medium not soil medium.


Ok onto the 2nd law of thermodynamics.

I'm just going to post what it is and you can draw a conclusion.

"The second law of thermodynamics states that the entropy of any isolated system always increases."

Entropy:

"Entropy and the Second Law of Thermodynamics If a china mug is dropped on the floor and breaks into many pieces, we accept this as a normal process. If the mug were to put itself back together and jump back into our hand we would consider this a most abnormal process. It is the Second Law of Thermodynamics which provides the principle that governs the ordering of events. It can be said that it determines the direction of time. The Second Law of Thermodynamics can be stated in terms of the entropy of a system. The concept of entropy is used to describe the degree of order in a system."

I need more Orange Sunshine to make that leap Ed/you describe.

Maybe that's the source of the flushing paradigm. I dunno but it's clever. It sounds good.
 
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Emeraldo

Well-Known Member
Uhm, right. So Ed Rosenthal maybe is the source of all this garbage about flushing for the purpose of diluting a fertilizer overdose. But you think he's wrong and what he says goes against all plant science. That's what I thought you were going to say, but just wanted to give you a chance to recant and become a flusher.

But Dr. Ed is not alone. Just look around. There's Greg Green, too, in The Cannabis Grow Bible (2017) at pp. 262-63. The "soil flush" is an emergency procedure for returning the soil to about pH 7 after a spill or accidental pouring of too much fertilizer, maybe even in too high a concentration, into the soil. He devotes several pages to different situations and correspondingly different steps.

Greg Green is wrong too, I presume? Uh-huh, right.

Be well...
 
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bobrown14

Grow Journal of the Month: Dec 2017
Yeah dont really know what to say. Emergency flushing.. sounds like back tracking to me.

I get where the flush thing is coming from, Its just not what people think it is. Just trying to do my part to help folks understand better about some of the pseudo science and real science.

I mean we've been growing plants all our lives my wife and I, never did I ever see or hear of any of these weird practices until I started reading about how people grow weed.

Some practices are actually pretty bizarre.

It's like if a little works ok, well then lots works better??

For me, its try a little, and see how it grows and err on the side of caution. But that's just me.
 

Emeraldo

Well-Known Member
1827643
i need some serious help this happened after a 100-degree day and I don't know how to help it recover what do I do
This thread started out as a discussion of what was wrong with the plant in the picture. It emerged that the plant was in MIracle Grow soil, and the symptoms sound a lot like a fertilizer overdose. If Kokeman actually over-fertilized on top of the Miracle Grow slow-release chemicals in that killer soil, then it would have been enough to lock out water. Then, in the heat, wilted. Just like Dr. Ed said.

What happened to Kokeman? What happened to the plant?
 

bobrown14

Grow Journal of the Month: Dec 2017
Yeah dont really know what to say. Emergency flushing.. sounds like back tracking to me.

I get where the flush thing is coming from, Its just not what people think it is. Just trying to do my part to help folks understand better about some of the pseudo science and real science.

I mean we've been growing plants all our lives my wife and I, never did I ever see or hear of any of these weird practices until I started reading about how people grow weed.

Some practices are actually pretty bizarre.

It's like if a little works ok, well then lots works better??

For me, its try a little, and see how it grows and err on the side of caution. But thats just me.
 

Emeraldo

Well-Known Member
Yeah dont really know what to say. Emergency flushing.. sounds like back tracking to me.

I get where the flush thing is coming from, Its just not what people think it is. Just trying to do my part to help folks understand better about some of the pseudo science and real science.

I mean we've been growing plants all our lives my wife and I, never did I ever see or hear of any of these weird practices until I started reading about how people grow weed.

Some practices are actually pretty bizarre.

It's like if a little works ok, well then lots works better??

For me, its try a little, and see how it grows and err on the side of caution. But thats just me.
Ok, Bob, that is your view. I guess pot growers who grow in pots do this flushing thing sometimes, for various reasons, mostly to do with fert overdose and sometimes to do with pre-harvest prep. Growers like you who grow in the open ground do not flush because it is not possible to flush for them. Chacun a son gout. To each her own. ;)
 
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