University of Guelph paper- Flushing is a myth!

[Douglas.Curtis]

When I change my res during flowering, it's usually 5 days before harvest. It's also usually between 300 and 400ppm at this point.

I swap it out for pure r/o filtered water, less than 14ppm.

In 5 days, my res is near or slightly above 300ppm again (because excess/unused nutes have left the plants and entered the r/o water), and _I_ can taste a large difference.

(edit: This comment could have been worded better... my apologies)

I'll continue to flush my hydro.

 

[hush]

I don't think senescence is proof the flushing works, if anything it's null evidence.

Why does senescence occur on single flowers that were manually pollinated early on in the flowering cycle even though the res is still packed full of nutrients? I think that would be a valid bit of proof that senescence has no correlation to flushing.

 

[Weird]

except that the papers I posted showed great translocation via senescence and artificial ways to trigger some of which are flushing techniques

 

[White Beard]

Just to see if I’ve been keeping it all straight:

- #NotAllGrowers “flush their plants/medium” because the product tastes and smokes better
- The theory behind this has been the removal of unused nutrients from the plant/medium
- this study shows that nutrients are NOT being removed by flushing after all
- #NotAllGrowers agree that it still tastes better, etc if flushed, even if we don’t know why yet

Is that about it?

 

[Cvh]

I personally find my end product better when I harvest plants which are yellow and not green.
Be it that the yellowing comes from true senescence (age) or that it was forced senescence (flushing / depriving of nutrients).
I usually perform forced senescence so my plants can be harvested weeks sooner then waiting for true senescence.

In my personal understanding there are 2 meanings to the word flushing. One is for flushing the soil/media during growth to cleanse the soil. And the other meaning is when the grower wants to harvest yellow plants in a couple of weeks to trigger forced senescence by only giving water.

I'm not a scientist, I'm not even a native English speaker. But I have been growing for quite a lot of years (hydro, soilless, coco, soil both synthetic and organic) and I know from experience what gives me the best end product. Yellow(/ripe) plants with cloudy trichs.

 

[Gauss]

Just to see if I’ve been keeping it all straight:

- #NotAllGrowers “flush their plants/medium” because the product tastes and smokes better
- The theory behind this has been the removal of unused nutrients from the plant/medium
- this study shows that nutrients are NOT being removed by flushing after all
- #NotAllGrowers agree that it still tastes better, etc if flushed, even if we don’t know why yet

Is that about it?

Also hippies don't smoke weed anymore, it's all millennials now.


Cvh, most of the world's best scientists were/are not even native English speakers. We did have Hawking though, which is nice. Einstein for instance however never became a fluent English speaker.

 

[White Beard]

In my personal understanding there are 2 meanings to the word flushing. One is for flushing the soil/media during growth to cleanse the soil. And the other meaning is when the grower wants to harvest yellow plants in a couple of weeks to trigger forced senescence by only giving water.

Point taken, edit made for clarity, thanks!

Also hippies don't smoke weed anymore, it's all millennials now.

I’ve not met the millennial yet who can keep up with me and the pipe, but I’m always up for a pipefull

 

[Gauss]

Flushing will not cause true senescence because it is natural, but effectively we trick the plant to do it anyway. Senescence is when the organism reaches an age where the stress of resisting death becomes too great and it prepares to succumb.

 

[Cvh]

Flushing will not cause true senescence because it is natural, but effectively we trick the plant to do it anyway. Senescence is when the organism reaches an age where the stress of resisting death becomes too great and it prepares to succumb.

This is how I understand it also.

True senescence -> age
Forced senescence -> 'flushing' / depriving of nutrients

 

[Cvh]

I don't know if the article is correct about that 'flushing' doesn't lower the nutrient in the final end product. I have no means to do the test myself. (I have read the entire posted article and I have to say that all the testing appears to be well executed.)

But I do know that yellow plants cure in a much better end product then green plants.
Personally I always thought that it was the chlorophyll content which made the difference and not so much the nutrient content.

 

[TychoMonolyth]

^^^ me too.

 

[BongFu]

A few people here seem to think that flowers going yellow is a sign that flowers are "cannibalizing" the nutrients (BTW I cringe when I hear the word cannibalizing - discard any info from someone who uses this term; they clearly are clueless). All yellowing shows is the breakdown of chlorophyll by a dying plant and chlorophyll breakdown is largely independent of nutrients. It comes down to proteins and enzymes...Explanation here https://www.sciencedirect.com/science/article/pii/S0005272810007942

 

[xxPeacePipexx]

One hell of a thread as expected, and I suspected that the art and practice of Tobacco Farming and processing would surface. I have been working with Tobacco plants for years and have been involved with the tobacco forums as well where this subjects never discussed as it relays to the fertilizer application and the finishing processes, be it air, flu or even sun curing more than anything else.

Tobacco is generally grown though in sandy infertile soil like a lot of other herbs and the Nitrogen is generally only applied in excess if there's heavy rainfall.

If memory serves me, didn't this trend or practice evolve with heavy handed Dutch growers using cheap fertilizers to begin with? Could be wrong, but it is what I have heard for several decades.

 

[TychoMonolyth]

I've noticed yellowing leaves on the bottom just as it's stretching and certainly when flowers start forming. I might be wrong, but I suspect it's shedding older excess shaded leaves to redirect the energy to flowering.

 

[CannaRed]

Here's a article I found from Cannabis Business Times

Under normal growing conditions, when nutrient availability exceeds demand, plants will store nutrients. When availability is low, they will cannibalize older plant material, robbing NPK and magnesium, and moving them to needy growing points.

Think about that. Flushing causes nutrients, especially nitrogen, to be moved into the buds to support growth. So although growers aim to remove nitrogen from the buds by flushing, the plant concentrates nutrients in the buds from other places in the plant. These nutrient concentrations are less than if the plant were nourished during the flush week, but concentrating less in the plant biomass is entirely different than removing nutrients from the biomass.

To Flush or Not to Flush
Columns - Hort How-To
What exactly is being gained — and lost — in this commonly accepted practice?

April 1, 2016
Kerrie and Kurt Badertscher

Although “that is the question” is the rest of Willy Shakespeare’s original phrase, a majority of growers large and small would likely follow that line with: “There is no question … you have to flush.”

Flushing is the use of pure water during a time period leading up to harvest to leach nutrients from the root zone. It is commonly held to be an essential last step in the cultivation process, and is associated with coaxing flavor and smokeability from the product.

The motivation for understanding flushing actually has to do more with money, not cultivation. A five- to 10-day flush represents as much as 12.5 percent of the plant’s flower time. Plants do not add mass in the absence of nutrients, so the loss of yield at the height of the plant’s ability to produce it makes this flavor-enhancement technique an expensive one.

Also, the longer plants sit in a flower room, the more they cost. The turn rate for a flower room running eight-week plants is 52/8, or 6.5 turns room turns per year. If the plants can be brought in at seven weeks at or near “with flush” harvests, the turn rate for that flower space goes up to 7.4, representing a significant increase in production even though seven-week harvests generally will be smaller than eight-week harvests.

The potential to gain almost a whole additional crop through that flower space each year is sufficient enough not to ignore.

The Flushing Effect
Many ways exist to deliver nutrients from entirely media-sourced nutrients (true organic) or by the use of external nutrient delivery. The flush can have a different effect on different media.

Media has a profound influence on a grower’s nutrient program. Media and nutrients need to be matched for effective nutrient delivery. Some media can hold large reserves of water and nutrients, while others require constant irrigation.

Particles in mineral and organic soils have negative electric charges, which, while small, are strong enough to attract and hold positively charged potassium, calcium and magnesium (ions) among others. Soilless and organic media have the ability to build up nutrient reserves in the media when the plant is given even small amounts in excess of its uptake capability. Those reserves can be drawn on if the plant is not nourished on schedule, but this characteristic of soilless and organic media also can contribute to a buildup of excessive levels of nutrients, which, if left untreated, can result in plants suffering nutrient toxicity at worst and water uptake reduction at best.

The proper reaction to high nutrient concentrations is flushing — used to keep roots and the plant safe from damage by excessive nutrient levels.

Because organic media particles are negatively charged, negatively charged nitrate nitrogen and phosphate ions are repelled from the particles and are the first nutrients to leave the root zone when a flush is applied. Without nitrogen in the root zone, the plant’s biological processes will be starved, and it will turn to scavenging and moving nitrogen, phosphorous and potassium (NPK) and magnesium from older tissue to the current growing points.

Although positively charged nutrients are attracted to the media particles, sufficient amounts of water will dissolve the nutrients off the media particles and remove them from the root zone. Because of the media particles’ propensity for holding nutrient ions, flushing leaves the root zone of an organic media with a hard-to-predict nutrient profile.

Rockwool growing mediums do not have the electrical charge character of organic media and therefore cannot store nutrients other than where nutrient solution is trapped in pockets in the media. A flush of rockwool effectively removes all nutrients.

Plants, however, do not stop growing when they are being flushed. Rapidly expanding buds can be seen even while the flush is removing the nutrients.

High nutrient levels are not typical in nature, so when nutrients are encountered, all are welcome. In fact, at certain pHs, plants can uptake lethal nutrient concentrations. This also brings to mind the fact that once the nutrients have been flushed from the root zone, the chemistry is altered, and the pH is exposed to variations. This can further reduce nutrient absorption.

Under normal growing conditions, when nutrient availability exceeds demand, plants will store nutrients. When availability is low, they will cannibalize older plant material, robbing NPK and magnesium, and moving them to needy growing points.

Think about that. Flushing causes nutrients, especially nitrogen, to be moved into the buds to support growth. So although growers aim to remove nitrogen from the buds by flushing, the plant concentrates nutrients in the buds from other places in the plant. These nutrient concentrations are less than if the plant were nourished during the flush week, but concentrating less in the plant biomass is entirely different than removing nutrients from the biomass.

Now that the plant has found a way around the lack of NPK and magnesium, it needs calcium. But the calcium supply needed to complete potential growth is limited. Calcium is not relocatable; it is laid down in tissue cell walls and, thereafter, immobile. If all external nutrients are cut off, the plant will not be able to put on the new growth that captures water in the biomass, adding the majority of mass to new growth.

Calcium and magnesium are seldom cut off completely, however. Other than reverse-osmosis water, the water used to flush contains some amount of both calcium and magnesium. So even in flush, plants are typically receiving some critical nutrients, which means that plants generally do not totally stop adding weight. But the removal of nutrients does result in a significant reduction in plant growth.

A Simple Test for Growth
A simple test is to put two flower plants (unsupported – no trellis) on bathroom scales and watch how the weight varies over time. Each time the plant is watered, note the weight just before it’s watered. That weight will steadily increase through flower, and slow down or level off following a flush.

Compare that to a plant for which nutrients are not withheld during that last week. The mass of the nourished plant should surpass that of a flushed plant. That is not a guess, it is a certainty, which means that flushing costs yield. The difference between the final weight of the nourished plant and that of the flushed plant represents the yield that is forgone in the name of quality.

We believe most growers recognize they are trading yield in favor of the quality enhancements. But it is not clear they have an appreciation for what exactly that quality is costing them or what exactly is being gained.

To us, the concept that flushing somehow changes the chemistry in plant tissue that has been laid down for weeks requires a scientific explanation because that concept seems akin to claiming that the car engine is cleaner after washing the car’s hood. Nutrients are locked in the plant, and an external flush cannot undo the complex biology that locked them in.

The levels of nutrients concentrated in plant tissue are up to 1,000 times more concentrated than those nutrients in the root zone. One-hundred ppm nitrogen solutions produce plants whose leaves can contain upwards of 10,000 ppm of nitrogen. Since we have established that none of those 10,000 ppm are going anywhere but within the plant, we are looking for explanation of how that concentration is being reduced by a flush to the extent it can affect flavor. We haven’t found it yet.

This is significant cost we’re talking about here, and it should get every grower’s attention and nudge them to run their own trials to get real feedback to see what happens when they push the plants more.

Personal experience is the best teacher. There are thousands of plants out there right now that are just about to be flushed, and anyone can flush one set of plants, while nourishing another during the last week in flower. Keep the two harvested materials separate, and ensure equal drying/curing treatment. This isn’t scientific, but a large number of responses could drive some very interesting results.

A Theory Worth Testing
So if you want to help forward the cannabis-cultivation knowledge base, run that test on some of your plants and get back to us.

It can be dangerous to ask for data when you have laid down a position, since you may get data that doesn’t support that position. But that is science: You make a claim and test it. If the data comes back in support of not flushing, then growers may well want to rethink their growing plan. The impact of this could be significant, as cutting 12 percent off of a plant’s production time (by eliminating the flushing period) would have more impact on cost per gram than anything else we can think of, and it’s not hard to do.

If the data comes back in favor of flushing, we know we have not considered all the variables, and we will set out in search of those.

There is no question that flushing removes nutrients from the root zone, so the key question is whether flushing the root zone has any influence on the sensible qualities of the plant’s biomass — in particular, smokeability and taste control. In the meantime, we all get to exercise our brains a little.

About the Authors: Kerrie and Kurt Badertscher are co-owners of Otoké Horticulture LLC (OtokeHort.com), and authors of “Cannabis for Capitalists.” They have worked with large-scale cannabis producers for more than 5 years. Kerrie has been involved with plants her entire lifetime and earned certification as a Professional Horticulturalist by the 100-year-old American Society for Horticulture Sciences. Kurt brings his 34 years of corporate experience and operations management skills to bear on the business challenges of cannabis cultivation.

Editor's Note: If you conduct tests as suggested in this column, please share your results with CBT by emailing the columnists at [email protected].


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https://www.cannabisbusinesstimes.com/article/to-flush-or--not-to-flush/

 

[CannaRed]

https://magazine.cannabisbusinesstimes.com/article/june-2019/white-ash-vs-black-ash.aspx

White Ash vs. Black Ash
Is the longstanding popular belief that white ash is ‘good’ nothing more than a myth?

Dr. Allison Justice & Dr. Markus Roggen


When white smoke appears high up above St. Peter’s Square in Rome, Catholics around the world rejoice. A new pope has been chosen. Habemus papam! We have a pope! No more black smoke, but white smoke and joy.

But the smoke color seen by Catholics is not a direct sign of God. What they are observing is the result of burning paper and straw. The smoke color, either white or black, was controlled originally by burning dry (white) or damp (black) straw. Today additives are used to control the smoke color: Black smoke is achieved by including coal tar and sulfur; white smoke results from added sugar and pine rosin. (And don’t we all like some good rosin.)

Cannabis cultivators and connoisseurs have come to believe that, like the white smoke seen in St. Peter’s Square, white ash left behind in the bowl from smoking cannabis is a cause to celebrate. Black ash, they believe, signifies that the plant was not flushed to remove minerals, nitrates and pesticides. White ash, in contrast, symbolizes properly flushed, dried and cured material.

Cannabis users rejoice when ash is white, but are they worshiping false idols?

What if the color of the ash is not a divine sign but a serendipitous occurrence linked to secular, mundane factors?

A Chemical Background
Seeing divinity in fire and ash is not new or unique to cannabis consumption. Ash itself is a trinity; it is a complex mixture of charcoal, char and minerals.1 As is often the case, more knowledge and insight mean less mystique. But there are ways in which knowledge gained can open new opportunities. If we used to ask a burning bush for answers about divinity, we now look to a burned bush for answers about forest fires.2 Research into ash from wildfires points to burn temperature as the main factor in determining ash’s properties.3 With increasing combustion temperature, the charred organic material and organic nitrogen concentrations decrease, and the ash color lightens from black to gray to white.4 The lightest color ash is mostly made up of crystalline or amorphous inorganic compounds.5 Further research has yielded additional insight.

At burn temperatures below 450 degrees C, combustion is far from complete, and the ash from low-temperature combustion is rich in organic compounds, with carbon as the main component. The combustion process progresses with increasing temperatures (above 450 degrees C), and carbon becomes volatilized, meaning it turns into a gas. What remains is mineral ash, composed mainly of calcium, magnesium, sodium, potassium, silicon and phosphorous in the form of inorganic carbonates. When the temperatures increase even further (above 580 degrees C), the most common forms of minerals are oxides.6 Another victim of higher combustion temperature is the ash’s total nitrogen content, as nitrogen has a low temperature volatilization.7

Insights from Tobacco Ash
Cannabis consumers are not the first to be obsessed with the color of their ashes—the tobacco industry has studied ash color for quite a long time. Already 100 years ago, scientific literature explored the plant ingredients that support or inhibit tobacco burn. It was described that chlorides prevent complete combustion, which then inhibits flavor and aroma. Potassium salts of organic acids, on the other hand, aid in combustion and increase the fire-holding capacity.8

Realizing the importance of potassium salts and other alkali and alkali-earth metal salts, U.S. federal and state agricultural departments, along with academic institutions, began to study the effect of fertilizer use on tobacco smoke and ash.9 Researchers found that fertilizer treatment neither altered the alkali composition of the cured leaves, nor increased the sulfur levels in the leaves. What did make a big difference in tobacco smoke quality was the fermentation process, specifically the high concentration of chlorophyll in low-quality tobacco products.

Early on, white ash in tobacco cigars and cigarettes was accomplished by adding magnesium or calcium acids, nitrates or carbonates. Burning any of these acids in your cigarette will cause alkaline earth metal oxide to form, which imparts a white color to the ash that is left behind.10

The main takeaway is that white ash forms at high combustion temperatures and is mostly made up of minerals. This should lead us to question the doctrine that white ash comes from flushed cannabis plants.

A Flushing Theory Debunked

If ash color is not the sign of quality we thought it to be, what are the factors that affect the quality of a plant or plant part after harvest? If we look at relevant industries, such as tobacco or produce, we would think about nutrient content, humidity, temperature, the addition or removal of light, the reduction of the ripening gas, ethylene, and time.

In the general horticulture world, the word “flushing” refers to the act of running a known liquid through a plant’s root ball in order to change pH or media electrical conductivity (EC). To cannabis growers, flushing means something very different: It refers to growers using low-EC water for irrigation during the last few weeks prior to harvest. The thought is this “flushes” out the nutrients from the media which, in turn, flushes them from the plant. The theory is that this ultimately yields a better-smoking flower. We’ve heard explanations supporting this theory that make no sense, such as, “It removes minerals from the plant,” and we’ve heard more plausible theories, such as, “Nutrient deficiency encourages ripening.”

My immediate thoughts go to outdoor cannabis. What about cannabis grown in living soil? Media besides rockwool will never get to an EC low enough to cause true deficiency in a matter of a week or two.

The only scientific paper we’ve seen to date on cannabis and flushing is the thesis “Irrigation Management Strategies for Medical Cannabis in Controlled Environments,” written by Jonathan Stemeroff, while he was pursuing a master’s degree at The University of Guelph. In his thesis, Stemeroff completes a series of experiments testing the nutrient content of dried bud after flushing. He finds that in his numerous flushing experiments, elemental content is not depleted, and yield is not impacted. Basically, unless you are using a rockwool media, you will never lower EC enough to cause true deficiency in a one- to two-week period.

This research does not address the many other things that could be contributing to a better smoke, but it does destroy the theory that flushing removes nutrient elements from a plant. It also encourages the sustainable and cost-effective practice of not applying fertilizer in the last two weeks of growth, as element concentrations were not affected by the low-EC water. Further research should be conducted to complement this study examining the effect of flushing on carbohydrates, chlorophyll, etc.

Other Horticultural Practices for Better Smokability
Another horticultural practice growers perform to improve smokability is turning the growing lights off for a few days before harvest and using no lights during drying. This ritual is supported by numerous studies on various types of live plants and harvested/detached plant parts rapidly decreasing in chlorophyll with the absence of light. It is shown that reducing the amount of light given in the final two days before harvest and during drying slows the degradation of sugars, and decreases starch content.11, 12, 13 Perhaps jump-starting the degradation process before harvest does ultimately increase quality in terms of smokability, which we expect to be represented by a whiter ash color.

Furthermore, another method cultivators perform to increase a product’s smokability is to drop the temperature the last few weeks of the flowering cycle. The temperature drop increases the purple pigmentation to those varieties that have this genetic predisposition. Research has shown that photosystem shutdown causing chlorophyll degradation is increased at low temperatures, even with light. Could dropping the temperature and turning out the lights improve your product’s smokability and smoothness of smoke, and cause a whiter ash? Very possibly, but remember the challenge of removing resulting humidity and the increased risk for botrytis growth at lower temperatures.

What This Means
So, it appears the manipulation of temperature and light with the goal of chlorophyll degradation and sugar transformation are major contributors to a pleasant smoke and “white” ash, not a good pre-harvest “flush.” This is an example of how easy answers based on poorly informed beliefs likely are not correct. That said, rituals and belief systems that every grower brings into how they grow cannabis might still result in their desired outcome. Just keep in mind that putting a golden calf on top of your stash might mask the underlying scientific reasons for your success, therefore causing you to miss the opportunity to further improve upon your practices.

FOR MORE INFORMATION
Helpful resources (cited in this article) to deepen your knowledge.

1 Palaeogeography, Palaeoclimatology, Palaeoecology 291, 11–39

2 Science of the Total Environment 572 (2016) 1403–1413

3 Catena 111 (2013) 9–24

4 Geoderma 189–190 (2012) 369–380

5 Biogeochemistry 85, 91–118

6 Earth-Science Reviews 130 (2014) 103–127

7 EKOLOGIJA. 56 (2010) 144–152

8 Effect of some alkali salts upon fire-holding capacity of tobacco, Henry R. Kraybill, 1917

9 Composition and quality of Pennsylvania cigar-leaf tobacco as related to fertilizer treatment, D. E. Haley, J. B. Longenecker, Otto Olson

10 US Patent: US3251368

11 Plant and Cell Physiology, Vol. 33, Issue 8, December 1992

12 J Sci Food Agric (2010) Issue 2, Vol. 91: 355–361

13 Planta (2002) Vol. 215: 541–548

Dr. Allison Justice is the co-founder of SC Botanicals and the founder of The Hemp Mine. Dr. Markus Roggen is the founder of Complex Biotech Discovery Ventures.

 

[BongFu]

Here's a article I found from Cannabis Business Times






https://www.cannabisbusinesstimes.com/article/to-flush-or--not-to-flush/

The Cannabis Business Times is a terrible source to cite and in over 30 years in the Canna game Kurt is one of the biggest imbeciles Ive ever encountered. His dribble about flushing losing yield and quality is already disproven scientifically.

 

[mean mr.mustard]

A few people here seem to think that flowers going yellow is a sign that flowers are "cannibalizing" the nutrients (BTW I cringe when I hear the word cannibalizing - discard any info from someone who uses this term; they clearly are clueless). All yellowing shows is the breakdown of chlorophyll by a dying plant and chlorophyll breakdown is largely independent of nutrients. It comes down to proteins and enzymes...Explanation here https://www.sciencedirect.com/science/article/pii/S0005272810007942

This only describes chlorophyll.

It also elucidated the facts that much of the actions are unknown and the possibility of a multitude of physiological causes and effects are still present.

That was a lot of reading.

I don't have to cringe to communicate.

Clearly clueless would be a term to shove up your ass.

 

[BongFu]

This only describes chlorophyll.

It also elucidated the facts that much of the actions are unknown and the possibility of a multitude of physiological causes and effects are still present.

That was a lot of reading.

I don't have to cringe to communicate.

Clearly clueless would be a term to shove up your ass.

Lot of attitude for someone that demonstrated their complete ignorance. What makes plants green champ?

 

[TychoMonolyth]

I wish people would stop comparing growing tobacco and cannabis. They have about as much in common as Alfalfa and Sunflowers.