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Nutrient Leaching: A Study

conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
Few words about how nutrients are leached, which ones are leached and under what conditions. The source is Chapter 7 of "Trees, Crops, and Soil Fertility: Concepts and Research Methods" (2003). It's good addition to flushing discussion, where folklore still rules.



:smokin2:
 

conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
I’ll try, man.

Leaching is a scientific term for what cannabis growers refer to as flushing, commonly understood as washing away excess of nutrients from the growing medium.

Now sometimes it’s understood as “cleansing the buds”, which is an absolute fantasy. This just can’t happen!

What this study says is that water percolating through the medium has a neutral charge, so it picks up both cations and anions on its way down, but mostly anions, which are nitrates and sulphur. The only cations that get picked up are Ca and Mg, cause they’re more mobile.

The study was done on soils with low CEC though, which means that the higher it is the fewer the elements that get leached.

What is also important is that K and P are very rarely if ever flushed away. The same if you use ammonia form of nitrogen, the salts. These stay in medium for a very long time.
 

conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
It’s really simple. Soil can hold only a certain amount of cations and anions, which is counted as CEC (cation exchange capacity) and AEC (anion exchange capacity).

When water passes through soil it will scoop up those flowing freely and will bring them wherever it flows. But cause most of the cations are trapped in soil, very few will be released. It’s different with anions though, which have negative charge, so they can be flushed away. Most of the time these are nitrates, light nitrogen compounds.

AND THAT’S WHAT “FLUSHING” DOES - RELEASES NITRATES, WHICH IS WHY PLANTS GET YELLOW RAPIDLY!
 

bobrown14

Grow Journal of the Month: Dec 2017
Well said Con.

I'm going to go flush my toilet and leave my soil alone.

This is very interesting but one thing that we tend to over look are the soil microbes. For me they are how my plants uptake the nutrients they converted into a soluble form.

I would think flushing soil enough to leach out minerals would be enough to also wash away the microbial community.

So we wash out the nutrients and wash out the microbes right at the point in time when the plants need them going down the stretch in flower. There's likely enough sugars in the fan leaves to sustain the plant and even grow flowers but I can't see it being of any benefit. Specifically in soil in a container.

I've always said that the flush paradigm is really supplying the plant with proper amount of water when they need it the most running down the stretch. My plants drink 1-2 gallons of water every day last 3 weeks of flower.
 

conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
Yeah that’s another story. You’re basically destroying their home by drowning and compacting it and suffocating them :)

Flushing is a complete nonsense in all soil and high CEC systems if you wanna keep your plants happy... and if you have problem with too much stuff inside wtf do you pour so much?
 

bluter

Well-Known Member
Flushing is a complete nonsense in all soil and high CEC systems if you wanna keep your plants happy
when i first heard of flushing plants it was strictly in the context of a hydro grow.

when did flushing become a thing in soil ?
 

conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
i'd like to know that too :)
 

Weaselcracker

Nug of the Year: 2016 - Member of the Month: Sept 2015, Nov 2016 - Nug of the Month: Oct 2016 - Plant of the Month: May 2016
Conrad thanks for the info - you’re dead right as far as nobody is going to directly ‘wash out their buds’ by flushing.

I think there’s some confusion around the idea of ‘flushing’ and maybe a variety of different ways people are using it. It’s kind of a stupid term actually.

Around three weeks before the end of flowering I stop feeding, or just feed very lightly. I’m growing in peat moss/perlite- its a form of hydroponics. So for these last few weeks the plants generally get water only. It gives them a chance to use up their food supply, which they do. Their leaves turn yellow and the flowers become colourful, sticky, and ripe.

To my mind, starving the plant towards the end like this also sends a signal that it’s ‘fall’. It depletes its remaining resources and puts them into growing beautiful fruit.

I’m pretty sure this is called flushing- though I don’t use the term myself. I don’t really call it anything. It’s just late flowering. It seems perfectly legitimate.

Works for me anyway. The bud clearly ripens better this way, while plants that are fed right to the end look all wrong to me.

I don’t really see how it could work in soil, which is not something designed to be wiped clean of nutrients.
I can see how it would work well for a true hydroponic grow though.

 
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bobrown14

Grow Journal of the Month: Dec 2017
Yeah you are running what I call soil-less medium. As Con pointed out its not a high CEC medium so it can make some sense when incorporated with soil-less or hydro for sure. I'd just cut back on nutrients and water enough.

My thing is that yes the plants don't need a lot of nutrients down the stretch but they need some.

I'm fairly certain that your flowering fertilizers are already lower in soluble nutrients (or should be) as the plants are not using up as much energy late in flower. Kinda makes sense in the real world since the sun isn't out as long = less photosynthesis so less food. Plants still manage to make flowers.

Why those fan leaves are so important, specially in late flower.

I see a lot of growers cutting the fans off the plant. Thats another weird thing that we only see in the cannabis growing world.

I think the "flush" thing got wide popularity due to some "expert" wrote it in a book so it has to be true. First time I herd of flushing soil my common sense needle went spastic.
 

Weaselcracker

Nug of the Year: 2016 - Member of the Month: Sept 2015, Nov 2016 - Nug of the Month: Oct 2016 - Plant of the Month: May 2016
People just like control. Feed feed, train and twist, slice and dice, flush flush, chop chop.

Best to disconnect that common sense needle if you wanna make your way in this world. Your brain could spin right off
 
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conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
Yeah growing cannabis has often very little to do with common sense imo :)
 

Oldgrowth

Well-Known Member
My common sense prompts, at least for soil growing, that there are only a few independent variables to worry about. Once situated the basic concerns are nutrients, water and insect control. IMHO. The plant does most of the work thanks to evolution and some selective breeding. Spot on W about the control Jones that seems to have spilled over to soil growing for no demonstrated reason.
 

conradino23

Grow Journal of the Year: 2017 - Grow Journal of the Month: Sept 2017
Hydro came with indoor revolution in the 80s, then Dutch really went big with it and it had to be somewhere in the 90s that hydro logic crossed over through High Times, Cannabis Cup and books about growing.
 

bluter

Well-Known Member
Hydro came with indoor revolution in the 80s, then Dutch really went big with it and it had to be somewhere in the 90s that hydro logic crossed over through High Times, Cannabis Cup and books about growing.

it was the 80's when i first encountered flushing and it was solely in the context of hydro.

i think it crossed into soil with the advent of media like HP promix and other "soilless" soils. these are the soils devoid of any nutrient content. the grow philosophy behind those are they are a hydro type media like a non soil, and therefore many of the hydro practices cross over. i'm sure flushing simply came with it, then jumped to real soils.

a lot of people here use promix , and they all describe their method as soil grows, and they pretty much all flush.
 
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