A critical look at preharvest flushing

All this study about minerals in my grow may very well change my life. I feel healthier as I apply these same principles to all my gardens, and to ME. Mineral nutrition [chelated, always]. Now I see differently the concept "alkalize or die". It is not so much about pH, it's about minerals. A whole 'nother reason for 10 minutes to healthier happier you/me.
Thanks for sharing the ride!
 
I agree the concept is flawed. Rightly or not I have "flushed" before because I made a big mistake and my runoff was hot reading about 4650 ppm, I was aiming for 1750 ppm. I freaked out and started watering to rinse off some nitrogen.

It just never made sense to me to shut down plants just when they are at full throttle for weight gain and trichome development. So, I spent about 40 hours looking at the different ideas. Probably another 40 trying to figure out what the first 40 was about.In the end I learn why I am doing the things I do to my plants

Personally, I wean off nitrogen toward the end. I have come to a better understanding of the process of chlorophyll degradation in living plants. I got goofy with phosphates and sulphates, and stuff from the medicine cabinet and the kitchen cabinets and the refrigerator. Somewhere in this I must open a benevolent version of Pandora's box.

When these plants are allowed to senesce or late into flowering they begin to conserve their sugars. The plants roots stop bleeding sugars to the microbes. The microbes run out of energy and stop feeding the plant minerals and stuff. The plant makes seeds (or not) and runs out of energy due to the shortage of stuff from the microbes...I gotta stop some where, and all the players wait till next season. Flush twice, it's a long way to Chicago.

Happy Scientist
I believe I misunderstood the very issue I am trying to explain and follow in my own practices. I have made a horrible error. It is possible that learning has occurred. Nitrogen comes in different forms. I intend(ed) to wean off nitrated forms (NO3) and supplant them with ammoniacal forms (NH4).
Wow, if I could only find a quality study that looked at this single nutritive ion (Nitrate, NO3-) and how it relates to what we all want to accomplish I will post it. The studies all focus on the results but are not looking at the type of "flush" that was done.
I need to send an email to the International - Society of Home Weed Amateur Growers, I-SHWAG, and see if we can eliminate the term "flushing" and replace it with more descriptive terms for what is actually being accomplished. For example a Cal/Mag flush could be called a "Chelated Cal/Mag Boost"
Even though none of this is new. I believe we are on the edge of a breakthrough in understanding why one person will become sick while another remains healthy and it may well be some stoned burnout that comes up with the answer. I believe it is based on mineral nutrition. Chelation it nothing new either, I believe understanding minerals better is one of the secrets to optimum health for our plants and for us because we eat plants. Key-lation is the key.
 
I believe I misunderstood the very issue I am trying to explain and follow in my own practices. I have made a horrible error. It is possible that learning has occurred. Nitrogen comes in different forms. I intend(ed) to wean off nitrated forms (NO3) and supplant them with ammoniacal forms (NH4).
Wow, if I could only find a quality study that looked at this single nutritive ion (Nitrate, NO3-) and how it relates to what we all want to accomplish I will post it. The studies all focus on the results but are not looking at the type of "flush" that was done.
I need to send an email to the International - Society of Home Weed Amateur Growers, I-SHWAG, and see if we can eliminate the term "flushing" and replace it with more descriptive terms for what is actually being accomplished. For example a Cal/Mag flush could be called a "Chelated Cal/Mag Boost"
Even though none of this is new. I believe we are on the edge of a breakthrough in understanding why one person will become sick while another remains healthy and it may well be some stoned burnout that comes up with the answer. I believe it is based on mineral nutrition. Chelation it nothing new either, I believe understanding minerals better is one of the secrets to optimum health for our plants and for us because we eat plants. Key-lation is the key.


there are different types of chelation. how a mineral is chelated has a lot to do with availability, and determines the basis of your nutes. different nutes use entirely different methods of chelation.
 
You guys all rock. I've grown outdoor a couple times now inside a few times. Getting better as I go. Will give more info in the future and pic's but terrible with technology so please be patient with me. Scrogging now,will be done in a couple days would love some opinions on my ladies. Have pics though the whole process if I can figure out how to post them. Thanks again to all.
 
Well that was a mighty long read...

I do taper off feed towards the last week followed by a few days of a finishing agent (MgSO4, Sulphur), but my final watering before it goes into the dark is with a good splosh of 12% H2O2
The plant seems to dry more evenly initially and doesn't go through the lawn cuttings stage at all
It also cures into a nice pale green and the smell and flavour are improved in my experience

Since I can put essences into my water such as lemon, blueberry, vanilla etc to 'flavour' it, stands to reason that some residue of some kind does remain in the bud that you can taste
H2O2 means the plant's last supper is masses of oxygen and 100% pure water which, I believe is the reason the bud smokes so clean - whether it's the Oxygen to the roots or the pure water, something seems to work
This only applies to fully synthetic grows, probably irrelevant to soil growers

Whichever stance you wish to adopt, that's cool, enjoy :hookah:
 
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:

The nutrient uptake process is explained in this faq.

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.

‘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.

Translocation:
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.

Summary:
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.
Finally, thank you for providing a scientific approach that I have been trying to explain to others as well. I am a scientist and have been trying to explain that flushing does absolutely nothing. In the best case, flushing prevents any nutrients from being utilized by the plant thereby stunting any further biological processes. If that happen, status quo - no changes.
 
Back
Top Bottom