The Truth About Flushing

Discussion in 'General Marijuana Growing' started by riddleme, Feb 17, 2011.


    riddleme Well-Known Member

    There have been a lot of debates on this forum about flushing and there is a lot of misunderstanding about it in general flushing has its place in gardening and in the real world (other than MJ forums) is referred to as leeching

    This will be a long read but I hope it will set the record straight for everyone, this has been posted in several places here but I am putting to post together to clear things up a bit for all of you

    first a ditty from Sensi Seeds with links verifying,,,

    From an administrator at Sensi Seeds

    "Advanced - Flushing

    A critical look at preharvest flushing

    Pre harvest flushing is a controversial topic. Flushing is supposed to improve taste of the final bud by either giving only pure water, clearing solutions or extensive flushing for the last 7-14 days of flowering. While many growers claim a positive effect, others deny any positive influence or even suggest reduced yield and quality.

    The theory of pre harvest flushing is to remove nutrients from the grow medium/root zone. A lack of nutrients creates a deficiency, forcing the plant to translocate and use up its internal nutrient compounds.

    Nutrient fundamentals and uptake:

    A good read about plant nutrition can be found here.

    Until recently it was common thought that all nutrients are absorbed by plant roots as ions of mineral elements. However in newer studies more and more evidence emerged that additionally plant roots are capable of taking up complex organic molecules like amino acids directly thus bypassing the mineralization process.

    The major nutrient uptake processes are:

    1) Active transport mechanism into root hairs (the plant has to put energy in it, ATP driven) which is selective to some degree. This is one way the plant (being immobile) can adjust to the environment.

    2) Passive transport (diffusion) through symplast to endodermis. Proceedings/min_nutr.pdf

    The claim only ‘chemical’ ferted plants need to be flushed should be taken with a grain of salt. Organic and synthetic ferted plants take up mineral ions alike, probably to a different degree though. Many influences play key roles in the taste and flavor of the final bud, like the nutrition balance and strength throughout the entire life cycle of the plant, the drying and curing process and other environmental conditions.

    3) Active transport mechanism of organic molecules into root hairs via endocytosis.

    Here is a simplified overview of nutrient functions:

    Nitrogen is needed to build chlorophyll, amino acids, and proteins. Phosphorus is necessary for photosynthesis and other growth processes. Potassium is utilized to form sugar and starch and to activate enzymes. Magnesium also plays a role in activating enzymes and is part of chlorophyll. Calcium is used during cell growth and division and is part of the cell wall. Sulfur is part of amino acids and proteins.

    Plants also require trace elements, which include boron, chlorine, copper, iron, manganese, sodium, zinc, molybdenum, nickel, cobalt, and silicon.

    Copper, iron, and manganese are used in photosynthesis. Molybdenum, nickel, and cobalt are necessary for the movement of nitrogen in the plant. Boron is important for reproduction, while chlorine stimulates root growth and development. Sodium benefits the movement of water within the plant and zinc is neeeded for enzymes and used in auxins (organic plant hormones). Finally, silicon helps to build tough cell walls for better heat and drought tolerance.

    You can get an idea from this how closely all the essential elements are involved in the many metabolic processes within the plant, often relying on each other.

    Nutrient movement and mobility inside the plant:

    Besides endocytosis, there are two major pathways inside the plant, the xylem and the phloem. When water and minerals are absorbed by plant roots, these substances must be transported up to the plant's stems and leaves for photosynthesis and further metabolic processes. This upward transport happens in the xylem. While the xylem is able to transport organic compounds, the phloem is much more adapted to do so.

    The organic compounds thus originating in the leaves have to be moved throughout the plant, upwards and downwards, to where they are needed. This transport happens in the phloem. Compounds that are moving through the phloem are mostly:
    Sugars as sugary saps, organic nitrogen compounds (amino acids and amides, ureides and legumes), hormones and proteins.

    Not all nutrient compounds are moveable within the plant.

    1) N, P, K, Mg and S are considered mobile: they can move up and down the plant in both xylem and phloem.
    Deficiency appears on old leaves first.

    2) Ca, Fe, Zn, Mo, B, Cu, Mn are considered immobile: they only move up the plant in the xylem.
    Deficiency appears on new leaves first.

    Storage organelles:

    Salts and organic metabolites can be stored in storage organelles. The most important storage organelle is the vacuole, which can contribute up to 90% of the cell volume. The majority of compounds found in the vacuole are sugars, polysaccharides, organic acids and proteins though.


    Now that the basics are explained, we can take a look at the translocation process. It should be already clear that only mobile elements can be translocated through the phloem. Immobile elements cant be translocated and are not more available to the plant for further metabolic processes and new plant growth.

    Since flushing (in theory) induces a nutrient deficiency in the rootzone, the translocation process aids in the plants survival. Translocation is transportation of assimilates through the phloem from source (a net exporter of assimilate) to sink (a net importer of assimilate). Sources are mostly mature fan leaves and sinks are mostly apical meristems, lateral meristem, fruit, seed and developing leaves etc.

    You can see this by the yellowing and later dying of the mature fan leaves from the second day on after flushing started. Developing leaves, bud leaves and calyxes don’t serve as sources, they are sinks. Changes in those plant parts are due to the deficient immobile elements which start to indicate on new growth first.

    Unfortunately, several metabolic processes are unable to take place anymore since other elements needed are no longer available (the immobile ones). This includes processes where nitrogen and phosphorus, which have likely the most impact on taste, are involved.

    For example nitrogen: usually plants use nitrogen to form plant proteins. Enzyme systems rapidly reduce nitrate-N (NO3-) to compounds that are used to build amino-nitrogen which is the basis for amino acids. Amino acids are building blocks for proteins, most of them are plant enzymes responsible for all the chemical changes important for plant growth.

    Sulfur and calcium among others have major roles in production and activating of proteins, thereby decreasing nitrate within the plant. Excess nitrate within the plant may result from unbalanced nutrition rather than an excess of nitrogen.


    Preharvest flushing puts the plant(s) under serious stress. The plant has to deal with nutrient deficiencies in a very important part of its cycle. Strong changes in the amount of dissolved substances in the root-zone stress the roots, possibly to the point of direct physical damage to them. Many immobile elements are no more available for further metabolic processes. We are loosing the fan leaves and damage will show likely on new growth as well.

    The grower should react in an educated way to the plant needs. Excessive, deficient or unbalanced levels should be avoided regardless the nutrient source. Nutrient levels should be gradually adjusted to the lesser needs in later flowering. Stress factors should be limited as far as possible. If that is accomplished throughout the entire life cycle, there shouldn’t be any excessive nutrient compounds in the plants tissue. It doesn’t sound likely to the author that you can correct growing errors (significant lower mobile nutrient compound levels) with preharvest flushing.

    Drying and curing (when done right) on the other hand have proved (In many studies) to have a major impact on taste and flavour, by breaking down chlorophylls and converting starches into sugars. Most attributes blamed on unflushed buds may be the result of unbalanced nutrition and/or overfert and unproper drying/curing."

    Now with an actual botanical understanding of how this works we move on to yet another botanical proven fact that if plants are drowned, which occurs in nature in the form of floods they go into a survival fermentaion mode converting sugars into alcohol I am reposting my ditty on harvesting and curing so you can see the evidence of this,,,,,,,,,,,,

    Harvesting, Drying and Curing, A Research Study
    The first word we used for this research was Oxidation, the second word is Fermentation as the fermentation process is what makes "the cure" work so understanding the fermentation process is very important.

    Here at RIU there is a thread that includes a cut and paste from a book by Mel and Ed you all know I like Mels book I am not gonna paste it here as it is fairly long and this will be long enough as it is, but this same info appears on most every MJ forum and seems to be the basis for how we all cure today. It seems from my research that this was originally based on how tobaco is cured and we will get into that later, here is the RIU link to this info I advise you go read it then come back,,,,,,,,

    Harvesting Curing Drying - Take Back the Knowledge

    There is an old hippie growers myth that says to soak the roots in water for 3 to 10 days before harvest this is not to be confused with the flush that everyone talks about (you all know I don't flush before harvest, I flush always) the tip/myth is supposed to improve the quality of our smoke. I have to admit that I never paid it much attention until now because I have now proven it is not a myth and has some scientific validation.

    What it amounts to is a way to start the cure prior to harvest while the plant is still alive. This is an incredible find as far as I am concerned and I can not wait to try it. what it amounts to is starving the plant of oxygen by drowning it, if in hydro take away the bubbles or spray fill the tank with water and wait, if in a pot either continuously water it (keep it wet/soaked) or stick the pot in a bigger bucket of water.

    I need to add some background info as I'm getting ahead of myself, most of you know that if you add sugar and yeast together it ferments into alcohol giving off CO2. The basic definition of Fermentation is the act of breaking down sugars into alcohol and our plants do this internally thru a natural process even while growing. The act of fermentation is a oxidation/reduction process (explained in prior post) just as most plant functions seem to be. Also please be aware that N is needed for proper fermintation to take place.

    Here is the info I found verifying that this old hippie myth is real,,,,,

    MrMistery wrote>:(jules

    Plants use photosynthesis to make sugars out of water, CO2 and sunlight. But a plant cell (like any other cell) cannot use sugars for their cellular processes, it needs to break down the sugars and make ATP. Basically, the only difference between humans and plants in this chapter is that plants make their own sugars, while we get ours from food. But we still both need to use those sugars, and we do that through cellular respiration.

    Fermentation is strictly defined as any way of anaerobically degrade pyruvic acid and recycle NAD+ to keep glycolysis going. You can then categorize this process as lactic acid fermentation (where pyruvate accepts electrons from NADH directly and becomes lactate), alcoholic fermentation (where pyruvate is first decarboxylated to acetaldehyde which then accepts electrons from NADH to become ethanol) and others (which are much more obscure). So technically, human cells are able to carry out lactic acid fermentation. Liver cells also have the enzyme alcohol dehydrogenase (responsible for ethanol formation in yeast and other fungi), but we use it in the reverse direction so to speak to get rid of any alcohol which we consume by converting it to pyruvate.
    Plants however, can carry out alcoholic fermatation. They don't normally do it, because plants are usually in contact with oxygen. However, if you flood the root of a plant for about a week the cells are starved of oxygen, and because of this they will start carrying out alcoholic fermentation to survive.


    very true
    that is what my bio textbook says.
    just to complete the last part
    in alcoholic pathway ethanol forms a waste while the lactate formed in the lactate pathway can be broken down further. that is what leads to the oxygen debt
    found here,


    Alcoholic Fermentation In Plants

    By the following, which we find in the London Gardener's Chronicle, it will be seen that the discovery is somewhat akin to those of Prof. Burrill and others in this country:
    "When plants are deprived of oxygen gas it appears that alcohol is formed in all their tissues without the aid of any ferment. If a vegetable cell containing sugar be cut off from its supply of oxygen - be suffocated, in fact - the sugar it contains becomes broken up or changed into carbonic acid, alcohol, and other products. Moreover, the various alcoholic ferments only produce their effects under the same conditions. Alcoholic fermentation, then, depends solely on the suffocation of a living cell containing sugar. Starting from these ascertained facts, M. Van Tieghem, in a recent number of the Annales Agronomiques, alludes to a peculiar disease in apple trees[​IMG] due to a suffocation of the roots, followed by the production of alcohol in their tissues. On microscopic examination the tissues were found healthy, except the medullary rays, the cells of which, instead of containing starch or sugar, contained brown oily globules, the residue left after the formation of the alcohol, which latter is diffused throughout the root, tinging the cells of a characteristic brown color, and giving rise to an easily detected alcoholic odor.
    Judging from these appearances what was the nature of the disease, M. Van Tieghem made inquiries as to the character of the soil, and from this, as well as the fact that the season had been extremely wet, his diagnosis was confirmed, and he in consequence prescribed efficient drainage as the remedy for the disease, and with good effect.

    found here,

    one more

    I am giving you this info first as it relates to doing something prior to the actual harvest chop. The rest of what I found will bring everything that we find already posted in the harvest forum to a hopefully better understanding.

    We as MJ growers have modified/refined the basic knowledge of curing and fermentation of other plants due to the fact that our buds are not leaves and are therefore more subceptable to mold but the basic premise is the same, we don't add to much heat because it is known to degrade THC. We don't maintain higher humidity levels to avoid mold. The piling of the plants to induce fermentation is the same concept that makes composting work and for us home growers this is why we use a paper bag or cardboard box because it creates a scaled down compost/fermentation chamber, with this in mind pay great attention to why it is necessary to check often and rotate/rearrange the buds during this part of the process. Also know that this process will also continue once you put your buds into jars.

    I also want to point out that while it is easier to trim your buds before drying that leaving the leafs on and hanging the plant allows the leafs to dry formed around the bud to protect it from various things most importantly oxidation which we know degrades the THC. It also allows the buds to dry more slowly which is what we truely want to happen.
    My friend Shrubs did this on his second harvest, now I know why.

    Please remember that patience is a virtue the slower they dry the better they will be,,,,,,,,period. To many growers are in a hurry and as a result speed things up once you read all of the info I am about to present you will see what I am saying is true as I have (yes I have read all of it)

    Next I am going to share several MJ specific links about harvesting & curing as more heads are always better than one and the whole of all of them put together creates a pretty solid picture for us to consider as we try to improve our techniques. a couple of them even explain how to add flavors in case anyone wants to experiment a bit.

    Here they are in no particular order

    I am including the following links because they explain how other plants are cured in various different ways for color and taste this info will not only help us to better understand the various processes but may offer ideas for future experiments that might create a better end product. what you will see is while the techniques vary a bit they are all very similar.

    Cacao (chocolate)



    lots of other plants

    We're almost finished, I found a couple more things that I know will spark your DIY talents for technique tweaking LOL

    Here is a homemade drying chamber

    here is a homemade fermentation chamber

    in the comments section they mention an egg incubator that has adjustable heat and humidity for around $70, here it is

    and that brings us to the end of my research. I spent about 20 hours on all of this but you should be able to follow it all in just 2 or 3 since I was going thru 100's of pages to find the ones I have posted

    I hope that everyone that reads this comes away with a better understanding of how it all works and that as a result we all have better herb to enjoy in the future

    Happy Harvesting

    Lots of us here that follow this technique have had excellent results and have found that an extended dark period of 3~4 days speeds up the drowning/fermentation process

    Let the discussion begin :)


    dangerouseknowledge Well-Known Member

    wow quite a post let me read it lmao first reply on this one

    taint Well-Known Member

    Preharvest flushing puts the plant(s) under serious stress. The plant has to deal with nutrient deficiencies in a very important part of its cycle. Strong changes in the amount of dissolved substances in the root-zone stress the roots, possibly to the point of direct physical damage to them.
    Doesn't this happen every time you use the rain technique?.................if not why not?

    riddleme Well-Known Member

    2 reasons it does not, 1) it happens in mother nature all the time and the plants are programmed to respond to it and 2) we replace the medium with fresh nutes each time making them readily available
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    taint Well-Known Member

    That doesn't explain the stress caused by the change in the soil,it's the changs that causes the stress.
    How long between flushing and replacing the nutes?...............ya say ya let it dry out first.

    riddleme Well-Known Member

    it is PH'ing the water to that of rain 5.6 to 5.8 that stops the stress (as in mother nature) the plants go to sleep and then wake up when the sun comes out

    in soil I say wait because raining on soil releases built in nutes naturally and we don't wait till it's dry just till the top is dry a few inches down

    in soilless mediums we restore the nutes within hours I wait for one hour after they wake back up
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    taint Well-Known Member

    Can you explain how the ph prevents the stress caused by the change.
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    riddleme Well-Known Member

    When it rains the plants go to sleep, basically they hibernate until they see light then they wake up in hyperdrive mode to wick off the excess water it is what they are programmed to do in nature, we simply exploit it by raining often :)

    taint Well-Known Member

    Can you link the study for this please.

    riddleme Well-Known Member

    I do not have a link to anything my research covered many things and honestly I discovered by accident
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    riddleme Well-Known Member

    I totally do not mind debating my make it rain technique but not what this thread was meant for and there are a lot of growers here using the technique, it works and those doing it will atest to it

    nickman Active Member

    pretty interesting read ...

    taint Well-Known Member

    Allright,no prob.
    I was under the understanding this was about knowledge and differant ways to achieve real world results.
    I read everything you posted with a open mind,the material raises questions regards the methods you espouse so eloquently.
    My comment on the fermentation tech is if it's so great why doesn't commercially grown and packaged weed taste good.
    Usually only dry enough to bale then shipped is what I've seen.

    homebrewer Well-Known Member

    Anyone have any idea where the 'ash burns white' deal came from? A few stoners on Youtube who review product from local dispensaries always comment on the color of the ash and always try to link it to 'the plant was or wasn't finished properly'. Personally, I think it's total nonsense.

    TruenoAE86coupe Moderator

    I am in complete agreement homebrewer, hash that should burn to just white ash, weed gets sucked down the hole in the bong before it ever gets to white ash. I don't care how well you've flushed it or finished it, i have never smoked a bowl of weed to white ash, well at least not since i was a kid.
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    riddleme Well-Known Member

    all my buds burn down to a grey/white ash

    homebrewer Well-Known Member

    I guess the concept that I'm trying to wrap my head around is; how is the color of the ash in ANY way related to how the plant was finished? Where did this ash color idea even come from? The wood in my fireplace burns white but my trees aren't 'finished properly' before they're cut down, so where does this concept come from? More stoner forum nonsense or did this originate in hightimes or in a Cervantes book?

    TruenoAE86coupe Moderator

    Not in my bong they don't they suck through to black water. Maybe in a pipe but it is a very rare occasion i smoke out of a pipe, and never finish a bowl that far, yuck!
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    riddleme Well-Known Member

    I would say a little of both (truth & forum crap) if the bud has too much moisture in it it will burn black and if it is improperly dried and cured the bud can have unfermented sugars left behind that will also burn black but snap crackle & pop as well the forum crap is that this is the nutes that crackling

    riddleme Well-Known Member

    I keep a screen in my bong :)
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