To Flush or Not to Flush? 05-07-2010, 10:26 PM Posted By: jmansweed Member Views: 36,340 One controversial aspect of marijuana growth is "flushing.” In regards to this discussion I think we need to clearly define what exactly it is we're talking about. Flushing for our purposes typically implies using an unusually large amount of pH balanced water to essentially leach salt and/or nutrients from our medium, and hence our plant. Simply feeding your plant pH balanced water is not quite the same thing - allowing for excessive run-off, prior to harvest, is the real purpose. Many of us flush. Why? Obviously, because we like the results - cleaner smoke, a more natural flavor and healthier product are just some of our reasons - or excuses. What we need to do to is to develop a better understanding of what exactly the "flush" is accomplishing and really how healthy for the plant and our selves it may be. In researching this, one conclusion after the next led me to believe in it's irrelevance and then again, it's importance.



First I looked into how many regular crops are "flushed" prior to harvest. The practice is really not adhered to. I primarily looked into Tobacco crops as that plant also will be smoked. Very little information showed up, in fact most commercial farmers will apply only the nutrients and water needed, never any extra - it's a matter of economics. Excessive run-off in those conditions means food is washing away. It should have been more obvious to me initially, that tobacco companies are absolutely not worried abut removing excessive anything from they're product. I did find and interesting comparative study however, and will link the post at the end. In any case, It's important to understand what things we are trying to remove from the our plant. Most of us agree that primarily slowing photosynthesis, and hence eliminating chlorophyll will make our smoke taste smoother. This is where things get confusing however, or I should say they become clear.



Lets consider some general science to the plant we are growing, and then discuss our influences over it. Marijuana is an annual plant, this means in it's natural environment it will grow to maturity and if pollinated, will drop seed in a single season. Next season, it's seed will guarantee reproduction. Outdoors, this process occurs year after year given environmental conditions are typical. We all see this occur under the sun, season after season and typically never really consider why and how this can have influence over our indoor marijuana crop. All annuals experience an internal process triggered from what most believe to be primarily light cycle, called Senescence. An annual plant will begin to concentrate it's efforts into producing fruits and/or seed to insure future generations. This process is typically hormonally induced and begins when the light cycle begins to diminish. Eventually, under conditions related to senescence, the plant will slow photosynthesis on it's own and naturally draw nutrients from fan leaves to relocate energy into reproduction. So consider that out doors, under natural light deprivation, Annual plants will essentially "flush" themselves, basically to death, all to develop healthy seed. It is a natural and predictable process.



I had some very interesting conversations regarding this subject and was given a basic example of how plants choose they're time to go, regardless if we flush or not - under some conditions. If we had some heavily amended soil outdoors in our garden. We could easily grow multiple types of veggies and plants including marijuana in the same garden, in the same soil. Even with the different nutrient demands of the various plants they all thrive given the right food is in the soil. This is a perfect example of a plant choosing which and what nutrients it absorbs and when it absorbs them. This happens because the plant is reacting with the soil microbiology. Microbes like bacteria and fungi build relationships with plants and essentially trade nutrients for carbohydrate rich substances and various fluids assisting in microbial growth. It's known as a symbiotic relationship, one relies on the other.



So if an annual plant, interacting with soil life, chooses it's own uptake gathered conditions are correct, how much influence can we really have? The answer is easy, we have no influence in some conditions. Using some grow methods however, we have all the influence. Remember, adhering to strictly a plants natural and proven method of finishing it's life cycle is important to understand, however, marijuana itself has no intention of being smoked. Adding this unnatural process of flushing may result in a product more friendly to our purpose. We don't wait for apples to fall on the ground, we pick and eat them before the plant has given them to us. Many agricultural crops, grown under the strictest organic conditions are altered in the natural process to better provide us with product. Product that at times is tastier, more nutritious and generally healthier with human intervention.



Microbial life binds to organic matter. Under organic conditions - real bio-dynamic organics where all organic matter is added to soil prior to growing a plant, and microbial life is our priority. Flushing seems irrelevant. I said it. Irrelevant.



We are relying on microbial interaction and our feedings consist of typically water only in the first place. In fact, rich, organic soil will filter your water - run-off will literally be cleaner than the water added. I've flushed enormous amounts of water through organic soil, and indeed, I washed away soil life and plants showed stress. But stress was exactly it. I was now eliminated the plants known form of absorption. Yes this resulted in yellowing leaves, and the results indeed mimic senescence but what was I really accomplishing. I was forcing the plant to look to itself for food before her time, and really starving her to maturity rather than allowing her to naturally mature under normal conditions. The eventual results hypothetically should be the same. I starve the plant through excessive watering, or the plant starves itself through Senescence. With that theory in mind under strict organic conditions, in my opinion it is always wise to let the plant follow it's natural cycle when ever possible. Indoors, in controlled environments, when we switch our light cycle to 12/12 senescence essentially is triggered to begin. We do have some control however, seeding for example, is usually avoided. A plant will prolong growth when pollination does not occur. We can add growth hormones, things like sea weed and algae based additives which contain numerous growth hormones such as cytotoxins and gibberellins. Both contribute to extended growth and delayed Senescence. Many tricks of the trade can lead to larger yields and at times and extended harvest times. It is a soil food web that feeds our plants, a symbiotic environment that naturally harmonizes. Destroying the harmony, disrupting the balance can indeed induce stress and typical deficiencies, but regardless of what we add or take away, under organic conditions, the plant and it's relationship with microbial life dictate when maturity has arrived and when she is ready for harvest - not a flood of water. It should be noted that there can be exceptions to the above, such as smaller pots for example.



How about soiless mediums under organic conditions, i.e. Bio-organic. The majority of my grows are Bio-organic. I mix very little nutrients into my medium, and rely on weekly soluble, organic teas to feed my substrate. Feeding the substrate is important here as well as the above mentioned methods. Mediums like peat, pear-lite, coco, rock-wool and many variations of this style of grow still can maintain flourishing numbers of microbial life. The symbiotic relationship applies under these circumstances as well. However, remember microbial life actively binds itself to organic matter - plant roots included. How applicable would a flush be here? There is not nearly the same density of organic matter as most Bio-dynamic grows. The mediums included here are indeed more sensitive to flushing. My plants will react more quickly, yellowing faster and maturing quickly. Microbial life here has less matter to bind to, and although healthy root systems are intact we are more able to wash some of this life away. Plants can absorb nutrients in a multitude of ways. For this discussions purpose, lets consider the symbiotic relationship with microbial life as one and the plants ability to absorb nutrients directly (as in chelated nutrients) as another. Both are effective ways a plant will feed. One way however, allows us more influence in regards to flushing. Plants will rely more upon microbial life in soil and more on it's own means of absorption in hydro type environments. We still can and do use microbial interaction in hydroponic conditions but typically applied nutrients are plant ready. Bio-organics is a blend of hydroponics and soil in many ways, including nutrient absorption. Plants actively use both methods of absorption. Flushing does have it's place here, but timing is everything. Remember Senescence will occur displaying signals of maturity and plants will begin to essentially eat themselves.



Under Bio-Organic methods, I find flushing when the beginning of visual Senescence symptoms occur will greatly assist in producing cleaner smoke. Why? It's easier to dilute the available nutrients under these conditions. The substrate becomes less nutrient rich as we flush, microbial life is easier to literally wash away and the plants food source becomes more limited. Although this again can be viewed as stressing the plant, realize Senescence is eliminated nutrients at this point also, we simply are helping it along and indeed have the ability to, as our mediums provide less included organic matter to which microbial life would bind. I've directly compared this scenario - using peat based Pro-mix and results for me are the same time and again. Plants use they're supplies up more slowly relying on Senescence alone. They simply take longer to reach the stage and level of maturity I'm looking for. I actually find weight is temporarily increased with a flush. The buds swell, although after drying, production was almost identical as the unflushed plant. I see results flushing under Bio-organic conditions and make it a regular practice. Smoke is smoother and the buds take on a more mature, swollen look in my case. For the record, the unflushed plant received little nutrients the last feedings, which turned out to be only one extra. None the less, I recommend flushing under these conditions - at the right time - to help the plant draw nutrients from herself and eliminate chlorophyll more efficiently.



In my experiences with Aeroponics, DWC, Hydroton ebb and flo tables, and the more extreme forms of hydroponics that utilize loose, unstructured mediums, flushing also has benefits. Although microbes can indeed live on root systems and in reservoirs, the frequent flow of water makes it difficult for microbial life to bind to these mediums. Typically, under these conditions there is also a general lack of bio-mass. Lacking in bio-mass contributes to a lack of symbiotic life. Algae and bacteria can form "mats" and clog flow but that does not imply a thriving rhizosphere, visual populations of build up is not the same as a balanced, prolific environment. This general style of grow responds well to a flush. When growing organically or chemically nutrients can be washed away, and again timing is everything.



In almost any scenario, growing marijuana with chemical and synthetic based nutrients flushing has it's benefit. Most of us agree on this. Nutrient salts will build in many mediums and in plant tissue, specifically when plants are confined to a small area and leached frequently with salt based nutrients. I don't use chemical fertilizers and these days even avoid chemical blends, however, I've tested them many times and with solid results. In every instance when I would feed instead of flush in late flowering plants would remain deep green and retain excessive amounts of chlorophyll creating harsh smoke, as I usually put it - head ache weed. Any one who has bought a bag of Beasters (Canadian commercial herb), knows how quality slides with chemical fertilization programs that have no regard for a flush. Many chem based fertilizer programs can increase flowering time and weight with minor application changes. Nutrients do have a role in senescence and we can prolong the symptoms with proper or improper feedings, depending on our goals. The results of flushing are most apparent when using this method of nutrient application. Chemicals and synthetic salts will and do leach from the substrate rapidly. This is made clear by our ability to quickly improve or flush pH issues out mid cycle if necessary. Chemicals simply respond clearly to a flush. Even blended programs promote flushing. I believe as one example, Advanced Nutrients sells flushing additives that assist in salt removal. There is simply no denying that if you grow under theses conditions flushing is well practiced for good reason.



Which method will lead to healthier smoke has yet to be scientifically tested. Perhaps the effective flush we can give chemically fed plants draws more harm-full substances from the plant than not flushing an organic one. We have to consider the smoke. What happens to these nutrients when we burn them and what levels of items in the plant lead to harsh smoke or even worse, unhealthy marijuana. We all generally agree eliminated chlorophyll is a goal in flushing, (even the plant will try to do this on her own) but what other items do we want out of our plant at harvest time. I've heard people say weed will crackle when burned with excessive nutrients, specifically Nitrogen. I'm more prone to believing the herb may just be a little more moist than anticipated. Like wet wood. Others claim they can taste the chemicals - which I too have been guilty of. I've read that excessive amounts of Phosphorus can be harm-full when smoked, and even more so magnesium. Marijuana smoke also has high ammonium and alcohol numbers. It should be noted that THC burns at lower temperatures than the actual plant matter. If you want to truly eliminate many things from your smoke, Vaporizing your herb will probably be more efficient than actually flushing the plant prior to harvest. The point is to ultimately create healthier and smoother smoke. The color and carbon residues of smoke more dictate what may be left in our herb, and without scientific analysis we all are simply speculating here. The only real proof we have is results and our preferences. There is science to the flush that cannot be ignored, but the majority of us practice the technique. Its time however, that we all take a clear look at what it is doing for our smoke and when its applicable. Flushing is system and style dependent. I believe too many growers rule out flushing or adhere religiously to it with-out stopping to think about it's effectiveness and what we are trying to accomplish.



Sources : Urban Gardener - The Indoor Gardener - Maximum Yield - Susheng Gan : Senescence Processes in Plants - Charles Manning Child : Senescence and Rejuvenesence - https://www.erowid.org/plants/cannabi...is_info3.shtml - My years of experience



I also want to thank some members here at ICMag, who inspired the work here - https://www.icmag.com/ic/showthread.php?t=151506 - Members like MaryJohn, VerdantGreen, Microbe man, Stoned Crow, Darc Mind etc...............ICMag is lucky to have members like these guys!

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My nutrient study:

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