University of Guelph paper- Flushing is a myth!

[CannaRed]

Here's a link to a PDF. I can't copy and paste from pdf.

Basically they used 4 or 5 different flushing techniques.

No major difference of nutrient levels between the bud samples.

One pro from flushing is saving money on nutrients for last two weeks.

https://atrium.lib.uoguelph.ca/xmlui/bitstream/handle/10214/12125/Stemeroff_Jonathan_201712_Msc_with_erratum.pdf?sequence=8&isAllowed=y

What does everyone think?

 

[Elmer Bud]

Irrigation Management Strategies for Medical Cannabis in Controlled Environments
By
Jonathan Stemeroff
A Thesis
presented to
The University of Guelph
In partial fulfilment of requirements
for the degree of
Master of Science
in
Environmental Science
Guelph, Ontario, Canada
© Jonathan Stemeroff, November, 2017
Irrigation Management Strategies for Medical Cannabis in Controlled Environments
J. Stemeroff, MSc
Erratum Document for Previously Approved E-Thesis Submission
A post-approval (re)-examination of the raw data discovered unrecoverable errors in the
handling and reporting of the water potential data, with further issues regarding the nature of
the treatment differences. The general errors are:
1) Upon further review of the raw data logs it was discovered that the Control and Mild
Stress treatments were in fact the same (ref. page 38). Both treatments had the same
number of irrigation events (i.e. total water applied was the same) in all three trials.
The irrigation events were offset by 1-day but they both occurred at 2-day intervals.
a. Resolution – Any observed differences between the control and mild stress
treatment should be disregarded. Detected differences in agronomic and
metabolite production between the Control and Mild Stress treatments can only
be attributed to random chance and variation in the growth facility, not a
response to distinct irrigation regimes. Affected Figures – Disregard Control and
Mild Stress treatment effects in Figures 4.11 (page 54) and 4.13 (page 55)
2) Raw data was not properly filtered to remove erroneous readings (e.g., positive values
of plant water potential; non-sinusoidal or flat line response) resulting from instrument
fouling and condensation within the sensing chamber. The inclusion of erroneous data
resulted in skewed relationships between cumulative plant water potential and
cumulative vapour pressure deficit.
a. Resolution – Disregard the relationships depicted in Figures 4.1 (page 44), 4.2
(page 45), 4.3 (page 46), 4.4 (page 47), 4.5 (page 48), 4.6 (page 49), 4.7 (page
50), 4.8 (page 51), and 4.9 (page 52).
3) The apparent two-phase relationship between CWP and CVP shown in Figure 4.1 (page
44) and subsequently highlighted and independently analysed in Figures 4.2 (page 45)
and 4.3 (page 46), is the result of missing data (logger failure) during the middle phase
of the first growth cycle; the missing data was not properly accommodated resulting in
an apparent separation of the response relationship between early and late growth
periods. The subsequent analysis of flower cycles 2 and 3 included an analysis of this
artifact-based separation; as such, Figures 4.5 (page 48), 4.6 (page 49), 4.8 (page 51),
and 4.9 (page 52) are not meaningful as there is no data to suggest or support treating
the data as two distinct groups.
Based on the above errors, any conclusions outlined in section 6.1 (page 62-65) should also be
disregarded.
3
ABSTRACT
Irrigation Management Strategies for Medical Cannabis in Controlled Environments
Jonathan Stemeroff Advisor:
University of Guelph, 2017 Professor M.A. Dixon
Medical cannabis production is a new industry in Canada and represents a challenge
for the production of a repeatable and standardized product for medical use. A reliable and
reproducible environmental control strategy can contribute significantly to meeting this
challenge. Irrigation management and control of plant water status is one of the key
environmental control elements. To assess the effects of various irrigation management
strategies this study deployed in situ stem psychrometers to measure the water status of
plants. As a routine feedback device for irrigation control these devices are not ideal for
large-scale production so correlation with the key environment variable representing the
aerial demand for moisture (vapour pressure deficit) was assessed. By establishing a
relationship between cumulative water potential (cWP) and cumulative vapour pressure
deficit (cVPD) an irrigation management strategy that predicted plant water status based on
measurements of cVPD could be employed. Three treatments; control (irrigation events every
1-2 days), mild-stress (irrigation events every 2 days), and moderate-stress (irrigation events
every 3 days) were tested. The effects of flushing were also investigated to determine
whether it had the intended effect of reducing nutrient concentrations within the dried bud.
Through the use of psychrometers, water status (cWP) thresholds were correlated with
humidity (cVPD) thresholds and reduced irrigation frequency resulting in water use
reductions up to 45.7% which had negligible impacts on yield and cannabinoid profile.
Flushing was found to be ineffective in removing any significant amount of nutrient from the
bud.

 

[Elmer Bud]

G `day CR

Yep flushing is a myth !
How did people flush , before hydro ? Kinda hard to remove all the nutes from soil ?

Unflushed harsh weed ? BS !

Thanks for sharin

EB .

 

[CannaRed]

Thanks Elmer! . I was in process of typing it out on my phone.

And wasn't being fast.

Much appreciated

 

[CannaRed]

G `day CR

Yep flushing is a myth !
How did people flush , before hydro ? Kinda hard to remove all the nutes from soil ?

Unflushed harsh weed ? BS !

Thanks for sharin

EB .

I find it interesting that even fertigating till end showed no difference in nutrients.

I wonder if those plants were in senescence and not taking up nutes. But did they fade?
Plant is supposed to uptake what it wants.

Like everything else, learning something new just leads to more questions.

 

[BongFu]

Yep read this one about a year back on Glows site. No surprises there.... The idea that you could starve a plant and force it to access stored nutrients was always totally out there.

 

[SandyFantasyman]

.

 

[Elmer Bud]

I find it interesting that even fertigating till end showed no difference in nutrients.

I wonder if those plants were in senescence and not taking up nutes. But did they fade?
Plant is supposed to uptake what it wants.

Like everything else, learning something new just leads to more questions.

G `day CR

Mid to late flower the electrical charge of the roots decreases .
Equals less up take of nutes .

I hear you on the using up stored nutes angle .
But the idea that the minerals would be rinsed on back out always baffled me .

Flushed / unflushed , indoor / out door , organic / hydro .
Proof of the pudding is in the eating .

Thanks for sharin

EB .

 

[CannaRed]

I never really thought it was flushing the plant itself. I thought it was to flush the media.

 

[aridbud]

I don't care for the metallic, nutrient taste on inhale/exhale.....I'll continue to flush.

 

[Mr. Greengenes]

I think the word has been used to mean at least two different things. Some people use it to mean withholding nutrients (N) past peak flowering to get flower that's lower in chlorophyll at harvest. Other people just mean running water through the soil mix to 'flush' the excess nutrients from the medium itself, usually to correct an over feeding mistake.

Combining the two concepts gets me a bit confused. So water is run through the mix in an attempt to achieve low chlorophyll at harvest? I don't think that will work. Even just withholding the N doesn't work very well unless you're using a container size that restricts roots at peak flower.

As to whether cannabis grown with restricted nutrients during flower tastes and smells better, I'm pretty sure it does. It's the same with grapes, more flavorful but smaller. Besides, N during flowering builds more vegetative mass in the bud itself, which if you think like I do that trichome count is genetic, is basically reducing potency by increasing leaf mass. That might be an even better reason to limit nutrients during flower.

Just my 2c, anyway cool discussion!

 

[Dropped Cat]

Interesting, no doubt will challenge the folks who swear by the flush.

As I do salts in coco, low EC, 0.8, my reduction in nute strength to
0.4 EC the few days before chop is prepping the coco for re use.

The plants don't dissipate stored nutes through flushing anyway,
whatever is taken up stays there until its burned.


Good thread!

 

[Weird]

many plant trials are laughable in comparison to the methods being used in cultivation and in comparison to methodology that grows the best smoke chem, transitional or organic

 

[BongFu]

I think the word has been used to mean at least two different things. Some people use it to mean withholding nutrients (N) past peak flowering to get flower that's lower in chlorophyll at harvest. Other people just mean running water through the soil mix to 'flush' the excess nutrients from the medium itself, usually to correct an over feeding mistake.

Combining the two concepts gets me a bit confused. So water is run through the mix in an attempt to achieve low chlorophyll at harvest? I don't think that will work. Even just withholding the N doesn't work very well unless you're using a container size that restricts roots at peak flower.

As to whether cannabis grown with restricted nutrients during flower tastes and smells better, I'm pretty sure it does. It's the same with grapes, more flavorful but smaller. Besides, N during flowering builds more vegetative mass in the bud itself, which if you think like I do that trichome count is genetic, is basically reducing potency by increasing leaf mass. That might be an even better reason to limit nutrients during flower.

Just my 2c, anyway cool discussion!

Taste is a subjective thing. Everyones taste buds are different. The study found no yield losses occur by running water only for the last 14 days. This is because cell division is about nil towards the end of flower. The conclusion of the study being that running water only for the last two weeks is the go simply for saving money on inputs.

 

[troutman]

Feed only enough to keep the leaves evenly green and cut back 1/2 way thru flowering.

 

[Frylock]

I never bothered to flush really.... i never flushed vegetables or anything so don't see a need.

 

[dank.frank]

There are mobile elements and they absolutely do get used and depleted from the plants leaves, ie the reserves, if it can't get the nutrition from the roots. That's not even remotely debatable. It's called translocation.

I'll keep doing exactly what I do. Nothing but water 100% of the growing cycle.



dank.Frank

 

[paulo73]

Good thread on a very debatable theme. I tend to flush my indoor plants but after a couple of outdoor crops planted on heavily pre-fertilized soil ( it was where a pig breeder used to throw the pig shit during the early 2000´s, now it´s totally forbidden) where the end product was pretty much perfect to my taste made me think about the merits of flushing.
And what about the nutes translocation mentioned by Dank.Frank? Only from observation, too early&no time for research now, it seems logical to me.
As soon as you cut back feeding on the orchards the leaves start loosing the dark green color to lighter green. But that might only be a natural process due to fruit maturation and nothing relating nute intake.
Thanks anyway for making me think about it again.
To all of you i wish a great day.

 

[Gauss]

I've tested flushed and unflushed side by side, there is a noticeable difference in the final product no doubt. Flushed burns better, doesn't spark or sizzle, tastes cleaner near the end of the bowl, and smolders to a much softer ash. There is a big difference, I don't see how people can debate it unless they haven't tried it themselves or are doing things very differently than I nutritionally. I haven't tried it with every cut of every strain but I doubt it can vary much to where it wouldn't be noticeable when compared. If you gave me two nugs of the same cut and one was not flushed I am confident I could tell you which by only sampling one of them to the bottom of the bowl. Maybe it's not a nutrient factor, but the flush definitely makes a difference.

Tell them to test it in a bowl, that's where the answer really is to the questions that matter.

 

[BongFu]

There are mobile elements and they absolutely do get used and depleted from the plants leaves, ie the reserves, if it can't get the nutrition from the roots. That's not even remotely debatable. It's called translocation.

I'll keep doing exactly what I do. Nothing but water 100% of the growing cycle.



dank.Frank

But the mobile nutrients move to the areas of the plant where they are most needed - so the buds. This is counterproductive based on the flawed science that underpins flushing. i.e. the nutrients mobilise towards the buds which we then smoke.